其实我想看的是DrawerLayout, 但发现DrawerLayout里面是使用了ViewDragHelper去实现. 谷歌比较早就放出这个类了,但ViewDragHelper是开发中很少用到一个类.顾名思义这是一个和拖曳触摸有关的类. 本着追根溯源的想法, 加上ViewDragHelper的源码也不算多,就决定将ViewDragHelper的源码看一遍.对实现原理了解下.
代码一千多行,看完还是需要点时间的. 因此不会逐一讲完, 当然下面也会放出该类源码的解析,注释中也有一些个人理解的点写在里面. 有兴趣可以看看.所以这里直接讲下概括的东西,也足以对ViewDragHelper有个了解, 起码不至于陌生.
原理:
ViewDragHelper定义大量的常量状态值( 比如设定边缘触发拖曳事件的临界值,边缘大小, 可拖曳的边缘标记等等 )用于监听整个拖曳的开始到结束的过程.
这个过程主要分为三个步骤: 闲置状态( IDLE ), 运动( DRAG 或者 SETTLE ) , 闲置状态( IDLE ).
要知道,要令父view中的子view发生位移, 除了手动拖曳令子view同步跟着手势运动, 还可以通过设定结束位置的X,Y坐标和LEFT,TOP值来直接使子view移动到该指定位置. 前者是拖曳( DRAG ),拖曳的过程是有过渡动画效果的. 而后者就是SETTLE (这个词不好翻译, 直译是"安置"), 没有过渡动画, 就辣么直接出现在指定的位置.
但无论是前者还是后者, 整个拖曳或settle的过程, 一开始时子view是静止的, 叫闲置态( IDLE ), 然后手指在屏幕触摸拖曳, 当手势运动超过触发拖曳的临界值,子view就会被拖曳或者被settle, 当移动的过程结束, 又会变成闲置态(IDLE).
说说几个点:
1, ViewDragHelper的拖曳,比如drag,settle这些操作,是通过Scroller去实现的. (Scroller 是滑动事件的辅助类,非常有用, 写过类似上下拉等滑动效果的童鞋应该用过.)
2, ViewDragHelper的是有记录历史功能的, 事件的过程会将触摸的X,Y坐标存在数组中, 然后通过本地的System.arraycopy(Object src, int srcPos, Object dst, int dstPos, int length)方法,传递旧的的触摸坐标值到数组中保存.这使得拖曳过程是连贯的.
3, 有历史记录,当然也有清空记录的功能. ViewDragHelper提供了cancel()方法,类似onTouch的ACTION_UP事件. 当拖曳结束,或settle的过程结束, 可能系统还认为过程还在, 因此就需要提供的cancel()或abort()方法去终止这个过程,同时也自动调用clearMotionHistory()方法,置空历史记录.确保下次触摸拖曳事件是"新的开始".
4, 要理解触摸的点( pointer ),触摸事件和子view,父view在拖曳或settle中的相互关系.
手指触摸屏幕,刚接触屏幕肯定有一个点是先碰到的, 然后深按下去,手指的一定面积触摸到屏幕, 就意味着触摸动作是由一定数量的点( pointer )组成.这些pointer都有自己的X,Y坐标. 而能够响应拖曳或settle触摸事件的父view中如果子view所处的位置保证这些pointer是落在子view内的, 那这个子view才能被捕获到( be catured ). 子view被捕获到, 才能发生我们所看到的拖曳或settle过程. 当然,因为ViewDragHelper给view的边缘设定了大小, 也设定了触发view拖曳事件的临界值, 只有手指在屏幕边缘移动大于这临界值,才能使子view运动.(具体过程可参考源码)
5, ViewDragHelper的触摸拖曳事件,是针对父view最顶层的子view才会响应该事件.这个应该不难理解吧. 所以该类提供了public View findTopChildUnder(int x, int y)方法捕获父view中最顶层的子view对象.
6, ViewDragHelper 提供了强大的通讯接口 - Callback. 这是一个静态抽象类,定义了相当齐全的监听拖曳或settle过程各种状态的接口方法:
void onViewDragStateChanged(int state);
//当拖曳状态变更时回调该方法
void onViewPositionChanged(View changedView, int left, int top, int dx, int dy); //当捕获view由于拖曳或者设定而发生位置变更时回调
void onViewCaptured(View capturedChild, int activePointerId); //当子view被由于拖曳或被settle, 而被捕获时回调的方法.
void onViewReleased(View releasedChild, float xvel, float yvel); //当子view不再被拖曳时调用.如果有需要,fling的速度也会被提供.速度值会介于系统最小化和最大值之间.
void onEdgeTouched(int edgeFlags, int pointerId);
//当父view其中一个被标记可拖曳的边缘被用户触摸, 同时父view里没有子view被捕获响应时回调该方法.
boolean onEdgeLock(int edgeFlags);
//当原来可以拖曳的边缘被锁定不可拖曳时回调
void onEdgeDragStarted(int edgeFlags, int pointerId);
//当用户开始从父view中"订阅的"(之前约定允许拖曳的)屏幕边缘拖曳,并且父view中没有子view响应时调用.
等等.
Callback是理解ViewDragHelper的关键,因为它反映了开始移动到结束的监听过程.对了解ViewDrag事件有很大帮助.
7, 因为移动的子view肯定是View的子类, 因此ViewDragHelper还有延迟移动的功能,借助View的post()方法, Runnable接口实现.
8, ViewDragHelper通过EDGE_LEFT, EDGE_RIGHT, EDGE_TOP和EDGE_BOTTOM 来标记哪个边缘可被拖曳或settle. 从可拖曳或settle标记为不可拖曳或settle, 这个过程叫做被锁了( locked ). 因为CallBack提供的接口方法有监听这种状态变更的方法.
Then 几个点说到这,下面贴上源码解析. 有点长... 晚了, 具体的应用找个时间放在后面的文章再接着写.
/*
* Copyright (C) 2013 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.support.v4.widget;
import android.content.Context;
import android.support.v4.view.MotionEventCompat;
import android.support.v4.view.VelocityTrackerCompat;
import android.support.v4.view.ViewCompat;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.view.animation.Interpolator;
import java.util.Arrays;
/**
* @tranlator AlexTam
* ViewDragHelper是自定义ViewGroup时的实用类.它提供大量有用的操作和状态,来追踪用户在父View内的
* 拖曳子view和重新定位子view.(看到这里,估计就会想,要同步监听拖曳事件,肯定少不了在onTouch事件中随处用到的
* MotionEvent这个对象.是的,下面的确有它.)
*
* ViewDragHelper is a utility class for writing custom ViewGroups. It offers a number
* of useful operations and state tracking for allowing a user to drag and reposition
* views within their parent ViewGroup.
*/
public class ViewDragHelper {
private static final String TAG = "ViewDragHelper";
/**
* 空/无效的pointer ID
* A null/invalid pointer ID.
*/
public static final int INVALID_POINTER = -1;
/**
* 状态量:(IDLE是闲置的 意思)表示 view当前没有被拖曳或者运行的动画结束
* A view is not currently being dragged or animating as a result of a fling/snap.
*/
public static final int STATE_IDLE = 0;
/**
* 状态量: view当前正被拖曳.根据用户的输入或者模拟用户的输入,view当前位置发生改变.(表示,
* 用户怎么拖曳移动,view就根据拖曳的动作而发生位置改变.)
* A view is currently being dragged. The position is currently changing as a result
* of user input or simulated user input.
*/
public static final int STATE_DRAGGING = 1;
/**
* 状态量: 由于fling动作,或者预定的无交互的运动,view被"安置"到一个结束的地方.(可以想象,一个view被用户快速拖曳
* 并甩动,从而view被甩到某个结束的位置,的过程.)
* A view is currently settling into place as a result of a fling or
* predefined non-interactive motion.
*/
public static final int STATE_SETTLING = 2;
/**
* 标记可从左边缘拖曳.
* Edge flag indicating that the left edge should be affected.
*/
public static final int EDGE_LEFT = 1 << 0;
/**
* 标记可从右边缘拖曳.
* Edge flag indicating that the right edge should be affected.
*/
public static final int EDGE_RIGHT = 1 << 1;
/**
* 标记可从顶部拖曳.
* Edge flag indicating that the top edge should be affected.
*/
public static final int EDGE_TOP = 1 << 2;
/**
* 标记可从底部拖曳.
* Edge flag indicating that the bottom edge should be affected.
*/
public static final int EDGE_BOTTOM = 1 << 3;
/**
* 标记所有地方(边缘的上下左右)都能被拖曳.
* Edge flag set indicating all edges should be affected.
*/
public static final int EDGE_ALL = EDGE_LEFT | EDGE_TOP | EDGE_RIGHT | EDGE_BOTTOM;
/**
* 指引值:
*
* 表示a check(指引) 应该沿着水平轴发生.
* Indicates that a check should occur along the horizontal axis
*/
public static final int DIRECTION_HORIZONTAL = 1 << 0;
/**
* 表示a check 应该沿着垂直轴发生.
* Indicates that a check should occur along the vertical axis
*/
public static final int DIRECTION_VERTICAL = 1 << 1;
/**
* 表示a check可水平可垂直的发生.
* Indicates that a check should occur along all axes
*/
public static final int DIRECTION_ALL = DIRECTION_HORIZONTAL | DIRECTION_VERTICAL;
//将边缘大小定位20dp
private static final int EDGE_SIZE = 20; // dp
//时间值
private static final int BASE_SETTLE_DURATION = 256; // ms
private static final int MAX_SETTLE_DURATION = 600; // ms
// 当前的拖曳状态,值为idle, dragging or settling.
// Current drag state; idle, dragging or settling
private int mDragState;
// 在拖曳开始前的滑动位移.(可以这么理解,触发拖曳的最大临界值.)
// Distance to travel before a drag may begin
private int mTouchSlop;
// 上一次的位置或点
// Last known position/pointer tracking
private int mActivePointerId = INVALID_POINTER;
//初始化的X坐标
private float[] mInitialMotionX;
//初始化的Y坐标
private float[] mInitialMotionY;
//下面这些变量不写了噻,看名字也能知道.
private float[] mLastMotionX;
private float[] mLastMotionY;
private int[] mInitialEdgesTouched;
private int[] mEdgeDragsInProgress;
private int[] mEdgeDragsLocked;
private int mPointersDown;
private VelocityTracker mVelocityTracker;
private float mMaxVelocity;
private float mMinVelocity;
//边缘的大小,单位px
private int mEdgeSize;
private int mTrackingEdges;
//兼容新API所提供的Scroller
private ScrollerCompat mScroller;
//内部抽象类,提供一些规范的接口方法
private final Callback mCallback;
private View mCapturedView;
private boolean mReleaseInProgress;
private final ViewGroup mParentView;
/**
* 这个Callback是作为通信接口,当ViewDragHelper返回父view时使用."on"为首的方法是重要事件的回调方法,几个
* 接口方法用于提供更多关于请求父view的状态的信息给ViewDragHelper.这个抽象类同时提供子view拖曳的一些细节信息.
*
* A Callback is used as a communication channel with the ViewDragHelper back to the
* parent view using it. <code>on*</code>methods are invoked on siginficant events and several
* accessor methods are expected to provide the ViewDragHelper with more information
* about the state of the parent view upon request. The callback also makes decisions
* governing the range and draggability of child views.
*/
public static abstract class Callback {
/**
* 当拖曳状态变更时回调该方法.可看"STATE_"为首的常量了解更多信息.
* Called when the drag state changes. See the <code>STATE_*</code> constants
* for more information.
*
* @param state The new drag state
*
* @see #STATE_IDLE
* @see #STATE_DRAGGING
* @see #STATE_SETTLING
*/
public void onViewDragStateChanged(int state) {}
/**
* 当捕获view由于拖曳或者设定而发生位置变更时回调..
* Called when the captured view's position changes as the result of a drag or settle.
*
* @param changedView View whose position changed - 发生位置变更的view
* @param left New X coordinate of the left edge of the view - 新的左边缘X坐标
* @param top New Y coordinate of the top edge of the view - 新的顶部边缘Y坐标
* @param dx Change in X position from the last call - 从旧到新位置发生的X偏移值
* @param dy Change in Y position from the last call - 从旧到新位置发生的Y偏移值
*/
public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {}
/**
* 当子view被由于拖曳或设置(settle有点难翻译)而被捕获时回调的方法.提供拖曳的pointer的ID.
* 如果activePointerId被标记为{@link #INVALID_POINTER},它会代替没有初始化的pointer.
*
* Called when a child view is captured for dragging or settling. The ID of the pointer
* currently dragging the captured view is supplied. If activePointerId is
* identified as {@link #INVALID_POINTER} the capture is programmatic instead of
* pointer-initiated.
*
* @param capturedChild Child view that was captured
* @param activePointerId Pointer id tracking the child capture
*/
public void onViewCaptured(View capturedChild, int activePointerId) {}
/**
* 当子view不再被拖曳时调用.如果有需要,fling的速度也会被提供.速度值会介于系统最小化和最大值之间.
*
* Called when the child view is no longer being actively dragged.
* The fling velocity is also supplied, if relevant. The velocity values may
* be clamped to system minimums or maximums.
*
* <p>Calling code may decide to fling or otherwise release the view to let it
* settle into place. It should do so using {@link #settleCapturedViewAt(int, int)}
* or {@link #flingCapturedView(int, int, int, int)}. If the Callback invokes
* one of these methods, the ViewDragHelper will enter {@link #STATE_SETTLING}
* and the view capture will not fully end until it comes to a complete stop.
* If neither of these methods is invoked before <code>onViewReleased</code> returns,
* the view will stop in place and the ViewDragHelper will return to
* {@link #STATE_IDLE}.</p>
*
* @param releasedChild The captured child view now being released
* - 被捕获到的要释放的子view
* @param xvel X velocity of the pointer as it left the screen in pixels per second.
* - pointer离开屏幕X轴方向每秒运动的速率,单位是px.
* @param yvel Y velocity of the pointer as it left the screen in pixels per second.
* - pointer离开屏幕Y轴方向每秒运动的速率,单位是px.
*/
public void onViewReleased(View releasedChild, float xvel, float yvel) {}
/**
* 当父view其中一个被标记可拖曳的边缘被用户触摸, 同时父view里没有子view被捕获响应时回调该方法.
* Called when one of the subscribed edges in the parent view has been touched
* by the user while no child view is currently captured.
*
* @param edgeFlags A combination of edge flags describing the edge(s) currently touched
* - 描述所当前所触摸的位置的边缘标记, 如EDGE_LEFT,EDGE_RIGHT等等.
* @param pointerId ID of the pointer touching the described edge(s)
* - 触摸的点的ID.
*
* @see #EDGE_LEFT
* @see #EDGE_TOP
* @see #EDGE_RIGHT
* @see #EDGE_BOTTOM
*/
public void onEdgeTouched(int edgeFlags, int pointerId) {}
/**
* 该方法当原来可以拖曳的边缘被锁定不可拖曳时回调.如果边缘在初始化开始拖曳前被拒绝拖曳,就会发生前面说的这种情况.
* 但这个方法会在{@link #onEdgeTouched(int, int)}之后才会被回调.这个方法会返回true来锁定该边缘.或者
* 返回false来释放解锁该屏幕.默认的行为是后者(返回false来释放解锁该屏幕).
*
* Called when the given edge may become locked. This can happen if an edge drag
* was preliminarily rejected before beginning, but after {@link #onEdgeTouched(int, int)}
* was called. This method should return true to lock this edge or false to leave it
* unlocked. The default behavior is to leave edges unlocked.
*
* @param edgeFlags A combination of edge flags describing the edge(s) locked
* - 描述被锁定的边缘的边缘标记,如EDGE_LEFT等.
* @return true to lock the edge, false to leave it unlocked
* - 返回true来锁定该边缘.或者 返回false来释放解锁该屏幕.
*/
public boolean onEdgeLock(int edgeFlags) {
return false;
}
/**
* 当用户开始从父view中"订阅的"(之前约定允许拖曳的)屏幕边缘拖曳,并且父view中没有子view响应时调用.
*
* Called when the user has started a deliberate drag away from one
* of the subscribed edges in the parent view while no child view is currently captured.
*
* @param edgeFlags A combination of edge flags describing the edge(s) dragged
* - 描述该边缘的边缘标记,如EDGE_LEFT等.
* @param pointerId ID of the pointer touching the described edge(s)
* - pointer的ID.
* @see #EDGE_LEFT
* @see #EDGE_TOP
* @see #EDGE_RIGHT
* @see #EDGE_BOTTOM
*/
public void onEdgeDragStarted(int edgeFlags, int pointerId) {}
/**
* 调用设置子view z轴次序的参数.
* Called to determine the Z-order of child views.
*
* @param index the ordered position to query for
* @return index of the view that should be ordered at position <code>index</code>
*/
public int getOrderedChildIndex(int index) {
return index;
}
/**
* 返回拖曳的子view水平移动范围的值,单位为px.这个方法如果返回0,那么该view则不能水平移动.
* Return the magnitude of a draggable child view's horizontal range of motion in pixels.
* This method should return 0 for views that cannot move horizontally.
*
* @param child Child view to check - 目标子view
* @return range of horizontal motion in pixels - 水平拖曳的值,单位为px.
*/
public int getViewHorizontalDragRange(View child) {
return 0;
}
/**
* 返回拖曳的子view垂直移动范围的值,单位为px.这个方法如果返回0,那么该view则不能垂直移动.
* Return the magnitude of a draggable child view's vertical range of motion in pixels.
* This method should return 0 for views that cannot move vertically.
*
* @param child Child view to check
* @return range of vertical motion in pixels
*/
public int getViewVerticalDragRange(View child) {
return 0;
}
/**
* 当用户通过pointerId 输入特定值令目标子view移动时回调该方法.callback接口如果返回true,则表示用户
* 允许通过用于引导的pointer来拖曳该子view.
* Called when the user's input indicates that they want to capture the given child view
* with the pointer indicated by pointerId. The callback should return true if the user
* is permitted to drag the given view with the indicated pointer.
*
* 如果该子view已经被捕获, ViewDragHelper可能多次重复的调用该方法.多次的调用会导致新的pointer尝试去控制这个view.
* <p>ViewDragHelper may call this method multiple times for the same view even if
* the view is already captured; this indicates that a new pointer is trying to take
* control of the view.</p>
*
* 如果该方法返回true,并且当成功捕获到该子view时,方法{@link #onViewCaptured(android.view.View, int)}会随即被调用.
* <p>If this method returns true, a call to {@link #onViewCaptured(android.view.View, int)}
* will follow if the capture is successful.</p>
*
* @param child Child the user is attempting to capture - 用户视图捕获的子view
* @param pointerId ID of the pointer attempting the capture - 捕获该子view的pointerID.
* @return true if capture should be allowed, false otherwise - 如果允许并且捕获成功应该返回true.否则返回false.
*/
public abstract boolean tryCaptureView(View child, int pointerId);
/**
* 该方法用于限制子view沿水平拖曳的手势.默认的实现是,不允许水平手势.如果有类继承了该类,
* 必须覆盖重写该方法,并且提供值去限制该拖曳手势.
* Restrict the motion of the dragged child view along the horizontal axis.
* The default implementation does not allow horizontal motion; the extending
* class must override this method and provide the desired clamping.
*
*
* @param child Child view being dragged - 被拖曳的子view.
* @param left Attempted motion along the X axis - 沿X轴(水平)的手势
* @param dx Proposed change in position for left - view的left变更值
* @return The new clamped position for left - 对left返回新的位置值
*/
public int clampViewPositionHorizontal(View child, int left, int dx) {
return 0;
}
/**
* 该方法用于限制子view沿垂直拖曳的手势.默认的实现是,不允许垂直手势...(同上面的方法类似,就不过多解释了.)
* Restrict the motion of the dragged child view along the vertical axis.
* The default implementation does not allow vertical motion; the extending
* class must override this method and provide the desired clamping.
*
*
* @param child Child view being dragged
* @param top Attempted motion along the Y axis
* @param dy Proposed change in position for top
* @return The new clamped position for top
*/
public int clampViewPositionVertical(View child, int top, int dy) {
return 0;
}
}
/**
* 定义曲线动画的插值器
* Interpolator defining the animation curve for mScroller
*/
private static final Interpolator sInterpolator = new Interpolator() {
public float getInterpolation(float t) {
t -= 1.0f;
return t * t * t * t * t + 1.0f;
}
};
// 实现Runnable接口
private final Runnable mSetIdleRunnable = new Runnable() {
public void run() {
setDragState(STATE_IDLE);
}
};
/**
* 创建ViewDragHelper的工厂方法
* Factory method to create a new ViewDragHelper.
*
* @param forParent Parent view to monitor - 所要监听的父view
* @param cb Callback to provide information and receive events - 提供信息的Callback对象
* @return a new ViewDragHelper instance
*/
public static ViewDragHelper create(ViewGroup forParent, Callback cb) {
return new ViewDragHelper(forParent.getContext(), forParent, cb);
}
/**
* Factory method to create a new ViewDragHelper.
*
* @param forParent Parent view to monitor
* @param sensitivity Multiplier for how sensitive the helper should be about detecting
* the start of a drag. Larger values are more sensitive. 1.0f is normal.
* @param cb Callback to provide information and receive events
* @return a new ViewDragHelper instance
*/
public static ViewDragHelper create(ViewGroup forParent, float sensitivity, Callback cb) {
final ViewDragHelper helper = create(forParent, cb);
helper.mTouchSlop = (int) (helper.mTouchSlop * (1 / sensitivity));
return helper;
}
/**
* 应用应该使用ViewDragHelper.create()去获取新的实例.这将允许ViewDragHelper使用内部实现去兼容不同的平台版本.
* Apps should use ViewDragHelper.create() to get a new instance.
* This will allow VDH to use internal compatibility implementations for different
* platform versions.
*
* @param context Context to initialize config-dependent params from
* @param forParent Parent view to monitor
*/
private ViewDragHelper(Context context, ViewGroup forParent, Callback cb) {
if (forParent == null) {
throw new IllegalArgumentException("Parent view may not be null");
}
if (cb == null) {
throw new IllegalArgumentException("Callback may not be null");
}
mParentView = forParent;
mCallback = cb;
// ViewConfiguration是一个包含配置信息,如时间,位移等的配置类.
final ViewConfiguration vc = ViewConfiguration.get(context);
final float density = context.getResources().getDisplayMetrics().density;
mEdgeSize = (int) (EDGE_SIZE * density + 0.5f);
mTouchSlop = vc.getScaledTouchSlop();
mMaxVelocity = vc.getScaledMaximumFlingVelocity();
mMinVelocity = vc.getScaledMinimumFlingVelocity();
mScroller = ScrollerCompat.create(context, sInterpolator);
}
/**
* 设置最小速率.大于0px/s的速率能更好的被检测到.这样Callback就能恰当的运用该值去约束移动的速率.
* Set the minimum velocity that will be detected as having a magnitude greater than zero
* in pixels per second. Callback methods accepting a velocity will be clamped appropriately.
*
* @param minVel Minimum velocity to detect
*/
public void setMinVelocity(float minVel) {
mMinVelocity = minVel;
}
/**
* 获取最小速率. 值得注意的是,如果最小速率小于0, 那么直接返回0,不会返回比0小的值.
* Return the currently configured minimum velocity. Any flings with a magnitude less
* than this value in pixels per second. Callback methods accepting a velocity will receive
* zero as a velocity value if the real detected velocity was below this threshold.
*
* @return the minimum velocity that will be detected
*/
public float getMinVelocity() {
return mMinVelocity;
}
/**
* 获取当前helper的拖曳状态,返回结果为{@link #STATE_IDLE}, {@link #STATE_DRAGGING}
* or {@link #STATE_SETTLING}.中的其一.
*
* Retrieve the current drag state of this helper. This will return one of
* {@link #STATE_IDLE}, {@link #STATE_DRAGGING} or {@link #STATE_SETTLING}.
* @return The current drag state
*/
public int getViewDragState() {
return mDragState;
}
/**
* 设置允许父view的某个边缘可追踪.CallBack对象的{@link Callback#onEdgeTouched(int, int)} and
* {@link Callback#onEdgeDragStarted(int, int)}方法只有在边缘允许被追踪时才会调用.
* (就是说,如果不设置上下左右的某个边缘可追踪,那么这2个方法是不可用的.)
*
* Enable edge tracking for the selected edges of the parent view.
* The callback's {@link Callback#onEdgeTouched(int, int)} and
* {@link Callback#onEdgeDragStarted(int, int)} methods will only be invoked
* for edges for which edge tracking has been enabled.
*
* @param edgeFlags Combination of edge flags describing the edges to watch
* @see #EDGE_LEFT
* @see #EDGE_TOP
* @see #EDGE_RIGHT
* @see #EDGE_BOTTOM
*/
public void setEdgeTrackingEnabled(int edgeFlags) {
mTrackingEdges = edgeFlags;
}
/**
* 返回边缘大小的值.单位为px.这个值是该view边缘可以被监测或追踪的值的范围.
* Return the size of an edge. This is the range in pixels along the edges of this view
* that will actively detect edge touches or drags if edge tracking is enabled.
*
* @return The size of an edge in pixels
* @see #setEdgeTrackingEnabled(int)
*/
public int getEdgeSize() {
return mEdgeSize;
}
/**
* 在父view内捕获指定的子view用于拖曳.同时callback对象会被通知.但{@link Callback#tryCaptureView(android.view.View, int)}
* 不会被要求获取权限来捕获该view.
*
* Capture a specific child view for dragging within the parent. The callback will be notified
* but {@link Callback#tryCaptureView(android.view.View, int)} will not be asked permission to
* capture this view.
*
* @param childView Child view to capture
* @param activePointerId ID of the pointer that is dragging the captured child view
*/
public void captureChildView(View childView, int activePointerId) {
if (childView.getParent() != mParentView) {
throw new IllegalArgumentException("captureChildView: parameter must be a descendant " +
"of the ViewDragHelper's tracked parent view (" + mParentView + ")");
}
mCapturedView = childView;
mActivePointerId = activePointerId;
mCallback.onViewCaptured(childView, activePointerId);
setDragState(STATE_DRAGGING);
}
/**
* 返回当前捕获的view.如果没有捕获到的view,则返回null.
* @return The currently captured view, or null if no view has been captured.
*/
public View getCapturedView() {
return mCapturedView;
}
/**
* 当前拖曳捕获的view的点(pointer)的ID.
* @return The ID of the pointer currently dragging the captured view,
* or {@link #INVALID_POINTER}.
*/
public int getActivePointerId() {
return mActivePointerId;
}
/**
* 获取最小触发和初始化拖曳动作的值,单位px.
* @return The minimum distance in pixels that the user must travel to initiate a drag
*/
public int getTouchSlop() {
return mTouchSlop;
}
/**
* 这方法等价于onTouch中MotionEvent的ACTION_CANCEL事件.
* The result of a call to this method is equivalent to
* {@link #processTouchEvent(android.view.MotionEvent)} receiving an ACTION_CANCEL event.
*/
public void cancel() {
mActivePointerId = INVALID_POINTER;
clearMotionHistory();
if (mVelocityTracker != null) {
mVelocityTracker.recycle();
mVelocityTracker = null;
}
}
/**
* 中止取所有手势.并且直接结束动画.
* {@link #cancel()}, but also abort all motion in progress and snap to the end of any
* animation.
*/
public void abort() {
cancel();
if (mDragState == STATE_SETTLING) {
final int oldX = mScroller.getCurrX();
final int oldY = mScroller.getCurrY();
mScroller.abortAnimation();
final int newX = mScroller.getCurrX();
final int newY = mScroller.getCurrY();
mCallback.onViewPositionChanged(mCapturedView, newX, newY, newX - oldX, newY - oldY);
}
//中止了,当然要设置拖曳状态为闲置(或者说初始态)
setDragState(STATE_IDLE);
}
/**
* (使用这个方法,可以有动画效果的移动子view到特定位置,该位置需要给出的finalLeft和 finalTop值.)
* 随着动画,子view移动到既定(给定left和top值)的位置.如果这个方法返回true,会在后面随着手势移动的
* 每一帧中回调{@link #continueSettling(boolean)}方法,直至返回false.如果这个方法返回false,
* 就不会再移动去完成手势动作的事件.
*
* Animate the view <code>child</code> to the given (left, top) position.
* If this method returns true, the caller should invoke {@link #continueSettling(boolean)}
* on each subsequent frame to continue the motion until it returns false. If this method
* returns false there is no further work to do to complete the movement.
*
* 要注意的是,即使方法{@link #getCapturedView()}在这个滑动过程中仍会一直有效,可以获取catureView的值,
* 但这个操作过程不看做是一个捕获事件(我们应当知道,捕获子view不是我们决定的,是Helper自动在父view和
* 子view之间去自动完成的过程,无论这个过程成功还是失败).
*
* <p>This operation does not count as a capture event, though {@link #getCapturedView()}
* will still report the sliding view while the slide is in progress.</p>
*
* @param child Child view to capture and animate - 要捕获和添加动画移动的view对象
* @param finalLeft Final left position of child - 最终位置的left值
* @param finalTop Final top position of child - 最终位置的top值
* @return true if animation should continue through {@link #continueSettling(boolean)} calls
*/
public boolean smoothSlideViewTo(View child, int finalLeft, int finalTop) {
mCapturedView = child;
mActivePointerId = INVALID_POINTER;
boolean continueSliding = forceSettleCapturedViewAt(finalLeft, finalTop, 0, 0);
if (!continueSliding && mDragState == STATE_IDLE && mCapturedView != null) {
// If we're in an IDLE state to begin with and aren't moving anywhere, we
// end up having a non-null capturedView with an IDLE dragState
mCapturedView = null;
}
return continueSliding;
}
/**
* (通过这个方法,我们应当知道settle和slide的区别.前者是直接跳到结束位置,而后者是有过渡效果的.)
* 将捕获的view设置(settle)在给定的left,top值的位置.(表示,直接忽略过程,直接将view显示在特定位置)
* 这个过程中,该view(如果在此时已经有)适当的速度,则该速度会影响settle的过程.
* 如果这个方法返回true,方法{@link #continueSettling(boolean)}在整个settle过程中会被回调,直至返回false.
* 如果这个方法返回false,(表示此时该view已经在给定的位置)这个settle的过程就会结束,不会再工作完成事件.
*
* Settle the captured view at the given (left, top) position.
* The appropriate velocity from prior motion will be taken into account.
* If this method returns true, the caller should invoke {@link #continueSettling(boolean)}
* on each subsequent frame to continue the motion until it returns false. If this method
* returns false there is no further work to do to complete the movement.
*
* @param finalLeft Settled left edge position for the captured view
* @param finalTop Settled top edge position for the captured view
* @return true if animation should continue through {@link #continueSettling(boolean)} calls
*/
public boolean settleCapturedViewAt(int finalLeft, int finalTop) {
if (!mReleaseInProgress) {
throw new IllegalStateException("Cannot settleCapturedViewAt outside of a call to " +
"Callback#onViewReleased");
}
return forceSettleCapturedViewAt(finalLeft, finalTop,
(int) VelocityTrackerCompat.getXVelocity(mVelocityTracker, mActivePointerId),
(int) VelocityTrackerCompat.getYVelocity(mVelocityTracker, mActivePointerId));
}
/**
* 同样是将view直接设到特定位置(给定left, top值).
* (看该方法的实现,整个过程 也是靠scroller的scroll去实现的).
* Settle the captured view at the given (left, top) position.
*
* @param finalLeft Target left position for the captured view
* @param finalTop Target top position for the captured view
* @param xvel Horizontal velocity - 水平速度
* @param yvel Vertical velocity - 垂直速度
* @return true if animation should continue through {@link #continueSettling(boolean)} calls
* - settleing的过程中会一直返回true,否则返回false表示结束.
*/
private boolean forceSettleCapturedViewAt(int finalLeft, int finalTop, int xvel, int yvel) {
final int startLeft = mCapturedView.getLeft();
final int startTop = mCapturedView.getTop();
final int dx = finalLeft - startLeft;
final int dy = finalTop - startTop;
if (dx == 0 && dy == 0) {
// Nothing to do. Send callbacks, be done.
mScroller.abortAnimation();
setDragState(STATE_IDLE);
return false;
}
// 仔细看computeSettleDuration()这个计算时间的方法,其实挺复杂的.使用了相当多的运算处理.因此可以不看该方法的实现;
// 除非要继承ViewDrarHelper实现子类,实现更多效果...
final int duration = computeSettleDuration(mCapturedView, dx, dy, xvel, yvel);
mScroller.startScroll(startLeft, startTop, dx, dy, duration);
setDragState(STATE_SETTLING);
return true;
}
//该方法计算settle的时间
private int computeSettleDuration(View child, int dx, int dy, int xvel, int yvel) {
//clampMag(...)方法保证水平和垂直速度值不大于最大值, 也不小于最小值.
xvel = clampMag(xvel, (int) mMinVelocity, (int) mMaxVelocity);
yvel = clampMag(yvel, (int) mMinVelocity, (int) mMaxVelocity);
final int absDx = Math.abs(dx);
final int absDy = Math.abs(dy);
final int absXVel = Math.abs(xvel);
final int absYVel = Math.abs(yvel);
final int addedVel = absXVel + absYVel;
final int addedDistance = absDx + absDy;
final float xweight = xvel != 0 ? (float) absXVel / addedVel :
(float) absDx / addedDistance;
final float yweight = yvel != 0 ? (float) absYVel / addedVel :
(float) absDy / addedDistance;
//要注意的是getViewHorizontalDragRange(...)方法默认返回0,但一般都会在创建helper时传进的mCallback中重写该方法
int xduration = computeAxisDuration(dx, xvel, mCallback.getViewHorizontalDragRange(child));
int yduration = computeAxisDuration(dy, yvel, mCallback.getViewVerticalDragRange(child));
return (int) (xduration * xweight + yduration * yweight);
}
//该方法计算settle的时间,三个输入的参数依次分别是:水平或垂直方向的移动距离,水平或垂直方向的速度大小,拖曳范围值
private int computeAxisDuration(int delta, int velocity, int motionRange) {
if (delta == 0) {
return 0;
}
final int width = mParentView.getWidth();
final int halfWidth = width / 2;
final float distanceRatio = Math.min(1f, (float) Math.abs(delta) / width);
final float distance = halfWidth + halfWidth *
distanceInfluenceForSnapDuration(distanceRatio);
int duration;
velocity = Math.abs(velocity);
if (velocity > 0) {
duration = 4 * Math.round(1000 * Math.abs(distance / velocity));
} else {
final float range = (float) Math.abs(delta) / motionRange;
duration = (int) ((range + 1) * BASE_SETTLE_DURATION);
}
return Math.min(duration, MAX_SETTLE_DURATION);
}
/**
* 该方法通过最大和最小值,算出区间值.低于最小值返回0,大于最大值则返回最大值.
* Clamp the magnitude of value for absMin and absMax.
* If the value is below the minimum, it will be clamped to zero.
* If the value is above the maximum, it will be clamped to the maximum.
*
* @param value Value to clamp
* @param absMin Absolute value of the minimum significant value to return
* @param absMax Absolute value of the maximum value to return
* @return The clamped value with the same sign as <code>value</code>
*/
private int clampMag(int value, int absMin, int absMax) {
final int absValue = Math.abs(value);
if (absValue < absMin) return 0;
if (absValue > absMax) return value > 0 ? absMax : -absMax;
return value;
}
/**
* 这个方法和上面的clampMag(int value, int absMin, int absMax)几乎一样,只是换了浮点型.
* Clamp the magnitude of value for absMin and absMax.
* If the value is below the minimum, it will be clamped to zero.
* If the value is above the maximum, it will be clamped to the maximum.
*
* @param value Value to clamp
* @param absMin Absolute value of the minimum significant value to return
* @param absMax Absolute value of the maximum value to return
* @return The clamped value with the same sign as <code>value</code>
*/
private float clampMag(float value, float absMin, float absMax) {
final float absValue = Math.abs(value);
if (absValue < absMin) return 0;
if (absValue > absMax) return value > 0 ? absMax : -absMax;
return value;
}
private float distanceInfluenceForSnapDuration(float f) {
f -= 0.5f; // center the values about 0.
f *= 0.3f * Math.PI / 2.0f;
return (float) Math.sin(f);
}
/**
* 该方法类似上面的forceSettleCapturedViewAt(...),可参考之.
*
* Settle the captured view based on standard free-moving fling behavior.
* The caller should invoke {@link #continueSettling(boolean)} on each subsequent frame
* to continue the motion until it returns false.
*
* @param minLeft Minimum X position for the view's left edge
* @param minTop Minimum Y position for the view's top edge
* @param maxLeft Maximum X position for the view's left edge
* @param maxTop Maximum Y position for the view's top edge
*/
public void flingCapturedView(int minLeft, int minTop, int maxLeft, int maxTop) {
if (!mReleaseInProgress) {
throw new IllegalStateException("Cannot flingCapturedView outside of a call to " +
"Callback#onViewReleased");
}
mScroller.fling(mCapturedView.getLeft(), mCapturedView.getTop(),
(int) VelocityTrackerCompat.getXVelocity(mVelocityTracker, mActivePointerId),
(int) VelocityTrackerCompat.getYVelocity(mVelocityTracker, mActivePointerId),
minLeft, maxLeft, minTop, maxTop);
setDragState(STATE_SETTLING);
}
/**
* 这个方法在上面好几地方都被提及了.
* 在整个settle的过程中,这个方法会返回true.直至返回false,表示settle的过程结束.
* (该方法是内部调用的,外部建议不适用.)
*
* Move the captured settling view by the appropriate amount for the current time.
* If <code>continueSettling</code> returns true, the caller should call it again
* on the next frame to continue.
*
* 参数deferCallbacks - 如果要推迟滑动,比如在{@link android.view.View#computeScroll()}里面回调,或者view还在layout或者draw
* 的过程中,该参数应当传true;
* @param deferCallbacks true if state callbacks should be deferred via posted message.
* Set this to true if you are calling this method from
* {@link android.view.View#computeScroll()} or similar methods
* invoked as part of layout or drawing.
* @return true if settle is still in progress
*/
public boolean continueSettling(boolean deferCallbacks) {
if (mDragState == STATE_SETTLING) {
// 由于整个settle的过程都借助Scroller去实现,
// 因此keepGoing这个值也来自mScroller.computeScrollOffset();
// mScroller.computeScrollOffset()这方法,表示只要view处于scroll状态,都会返回true.停止scroll则返回false.
boolean keepGoing = mScroller.computeScrollOffset();
final int x = mScroller.getCurrX();
final int y = mScroller.getCurrY();
final int dx = x - mCapturedView.getLeft();
final int dy = y - mCapturedView.getTop();
if (dx != 0) {
mCapturedView.offsetLeftAndRight(dx);
}
if (dy != 0) {
mCapturedView.offsetTopAndBottom(dy);
}
if (dx != 0 || dy != 0) {
// 可见该方法在整个settle的过程中,由于位置的不断变化
// 会一直回调mCallback.onViewPositionChanged(...)的方法
mCallback.onViewPositionChanged(mCapturedView, x, y, dx, dy);
}
//这里很明显,当view已经去到最终位置,XY的坐标均相等时,即使keepGoing依然为true,系统以为
//该view依旧处于滑动中,但很显然,应该结束了.于是方法里面强制调用Scroller.abortAnimation()去中止动画,并
//向mScroller标记完成状态.keepGoing自然就为false了.
if (keepGoing && x == mScroller.getFinalX() && y == mScroller.getFinalY()) {
// Close enough. The interpolator/scroller might think we're still moving
// but the user sure doesn't.
mScroller.abortAnimation();
keepGoing = false;
}
//此处推迟滑动,借助Runable接口去实现
if (!keepGoing) {
if (deferCallbacks) {
mParentView.post(mSetIdleRunnable);
} else {
//来到这里,keepGoing和deferCallbacks为false,表示整个settle过程都结束了.
//更改拖曳状态,continueSettling(...)不会再被回调.
setDragState(STATE_IDLE);
}
}
}
return mDragState == STATE_SETTLING;
}
/**
* (该方法是当完成settle过程后释放捕获到的view对象, 内部方法,不必了解详细过程.)
* 正如所有接口事件的方法,这个方法也必须在UI主线程中使用.在释放的过程中,只会调用一次
* {@link #settleCapturedViewAt(int, int)}或者{@link #flingCapturedView(int, int, int, int)}方法.
*
* Like all callback events this must happen on the UI thread, but release
* involves some extra semantics. During a release (mReleaseInProgress)
* is the only time it is valid to call {@link #settleCapturedViewAt(int, int)}
* or {@link #flingCapturedView(int, int, int, int)}.
*/
private void dispatchViewReleased(float xvel, float yvel) {
mReleaseInProgress = true;
mCallback.onViewReleased(mCapturedView, xvel, yvel);
mReleaseInProgress = false;
if (mDragState == STATE_DRAGGING) {
// onViewReleased didn't call a method that would have changed this. Go idle.
setDragState(STATE_IDLE);
}
}
//下面几个"clear"为首的方法都是清空历史记录了
private void clearMotionHistory() {
if (mInitialMotionX == null) {
return;
}
Arrays.fill(mInitialMotionX, 0);
Arrays.fill(mInitialMotionY, 0);
Arrays.fill(mLastMotionX, 0);
Arrays.fill(mLastMotionY, 0);
Arrays.fill(mInitialEdgesTouched, 0);
Arrays.fill(mEdgeDragsInProgress, 0);
Arrays.fill(mEdgeDragsLocked, 0);
mPointersDown = 0;
}
private void clearMotionHistory(int pointerId) {
if (mInitialMotionX == null) {
return;
}
mInitialMotionX[pointerId] = 0;
mInitialMotionY[pointerId] = 0;
mLastMotionX[pointerId] = 0;
mLastMotionY[pointerId] = 0;
mInitialEdgesTouched[pointerId] = 0;
mEdgeDragsInProgress[pointerId] = 0;
mEdgeDragsLocked[pointerId] = 0;
mPointersDown &= ~(1 << pointerId);
}
//这个方法很明显是内部调用的,在saveInitialMotion(...)中调用.
//因为mInitialMotionX数组里面保存有触摸X坐标的缓存信息,该方法确保mInitialMotionX一直保存最新的pointerId值
private void ensureMotionHistorySizeForId(int pointerId) {
if (mInitialMotionX == null || mInitialMotionX.length <= pointerId) {
float[] imx = new float[pointerId + 1];
float[] imy = new float[pointerId + 1];
float[] lmx = new float[pointerId + 1];
float[] lmy = new float[pointerId + 1];
int[] iit = new int[pointerId + 1];
int[] edip = new int[pointerId + 1];
int[] edl = new int[pointerId + 1];
//这个过程,将触摸的X,Y坐标,上次触摸的X,Y坐标等信息复制过去
if (mInitialMotionX != null) {
//这里调用本地C方法去将mInitialMotionX的内存复制给imx数组,没源码...
System.arraycopy(mInitialMotionX, 0, imx, 0, mInitialMotionX.length);
System.arraycopy(mInitialMotionY, 0, imy, 0, mInitialMotionY.length);
System.arraycopy(mLastMotionX, 0, lmx, 0, mLastMotionX.length);
System.arraycopy(mLastMotionY, 0, lmy, 0, mLastMotionY.length);
System.arraycopy(mInitialEdgesTouched, 0, iit, 0, mInitialEdgesTouched.length);
System.arraycopy(mEdgeDragsInProgress, 0, edip, 0, mEdgeDragsInProgress.length);
System.arraycopy(mEdgeDragsLocked, 0, edl, 0, mEdgeDragsLocked.length);
}
mInitialMotionX = imx;
mInitialMotionY = imy;
mLastMotionX = lmx;
mLastMotionY = lmy;
mInitialEdgesTouched = iit;
mEdgeDragsInProgress = edip;
mEdgeDragsLocked = edl;
}
}
// 在这里,连同pointerId,保存X,Y轴坐标信息
// 也许看到这里,你已经猜到,pointerId这个值是递增的,由系统自动分配.
private void saveInitialMotion(float x, float y, int pointerId) {
ensureMotionHistorySizeForId(pointerId);
mInitialMotionX[pointerId] = mLastMotionX[pointerId] = x;
mInitialMotionY[pointerId] = mLastMotionY[pointerId] = y;
mInitialEdgesTouched[pointerId] = getEdgesTouched((int) x, (int) y);
// 或运算后再进行左移运算.
mPointersDown |= 1 << pointerId;
}
private void saveLastMotion(MotionEvent ev) {
final int pointerCount = MotionEventCompat.getPointerCount(ev);
for (int i = 0; i < pointerCount; i++) {
final int pointerId = MotionEventCompat.getPointerId(ev, i);
final float x = MotionEventCompat.getX(ev, i);
final float y = MotionEventCompat.getY(ev, i);
mLastMotionX[pointerId] = x;
mLastMotionY[pointerId] = y;
}
}
/**
* 检查给定id的pointer是否当前按下的pointer.
* Check if the given pointer ID represents a pointer that is currently down (to the best
* of the ViewDragHelper's knowledge).
*
* 被用于报告这个pointer信息的有以下几个方法:shouldInterceptTouchEvent()和processTouchEvent().
* 如果这其中一个方法都没有被相关的触摸事件回调,那么该方法中所汇报的信息是不准确或者过时的.
* (很明显,最新的触摸信息,必须是当前InterceptTouchEvent事件中能回调的.)
*
* <p>The state used to report this information is populated by the methods
* {@link #shouldInterceptTouchEvent(android.view.MotionEvent)} or
* {@link #processTouchEvent(android.view.MotionEvent)}. If one of these methods has not
* been called for all relevant MotionEvents to track, the information reported
* by this method may be stale or incorrect.</p>
*
* @param pointerId pointer ID to check; corresponds to IDs provided by MotionEvent
* @return true if the pointer with the given ID is still down
*/
public boolean isPointerDown(int pointerId) {
return (mPointersDown & 1 << pointerId) != 0;
}
void setDragState(int state) {
mParentView.removeCallbacks(mSetIdleRunnable);
if (mDragState != state) {
mDragState = state;
mCallback.onViewDragStateChanged(state);
if (mDragState == STATE_IDLE) {
mCapturedView = null;
}
}
}
/**
* 通过传进的pointerId,试图捕获view.如果之前已成功捕获过,则不再调用mCallback.tryCaptureView()方法,而直接返回true.
* Attempt to capture the view with the given pointer ID. The callback will be involved.
* This will put us into the "dragging" state. If we've already captured this view with
* this pointer this method will immediately return true without consulting the callback.
*
* @param toCapture View to capture
* @param pointerId Pointer to capture with
* @return true if capture was successful
*/
boolean tryCaptureViewForDrag(View toCapture, int pointerId) {
if (toCapture == mCapturedView && mActivePointerId == pointerId) {
// Already done!
return true;
}
if (toCapture != null && mCallback.tryCaptureView(toCapture, pointerId)) {
mActivePointerId = pointerId;
captureChildView(toCapture, pointerId);
return true;
}
return false;
}
/**
* 测试是否view v是否能滑动
* Tests scrollability within child views of v given a delta of dx.
*
* @param v View to test for horizontal scrollability
* @param checkV Whether the view v passed should itself be checked for scrollability (true),
* or just its children (false).
* @param dx Delta scrolled in pixels along the X axis
* @param dy Delta scrolled in pixels along the Y axis
* @param x X coordinate of the active touch point
* @param y Y coordinate of the active touch point
* @return true if child views of v can be scrolled by delta of dx.
*/
protected boolean canScroll(View v, boolean checkV, int dx, int dy, int x, int y) {
if (v instanceof ViewGroup) {
final ViewGroup group = (ViewGroup) v;
final int scrollX = v.getScrollX();
final int scrollY = v.getScrollY();
final int count = group.getChildCount();
// Count backwards - let topmost views consume scroll distance first.
for (int i = count - 1; i >= 0; i--) {
// TODO: Add versioned support here for transformed views.
// This will not work for transformed views in Honeycomb+
final View child = group.getChildAt(i);
if (x + scrollX >= child.getLeft() && x + scrollX < child.getRight() &&
y + scrollY >= child.getTop() && y + scrollY < child.getBottom() &&
canScroll(child, true, dx, dy, x + scrollX - child.getLeft(),
y + scrollY - child.getTop())) {
return true;
}
}
}
return checkV && (ViewCompat.canScrollHorizontally(v, -dx) ||
ViewCompat.canScrollVertically(v, -dy));
}
/**
* 检测这个作为被提供给父view的onInterceptTouchEvent的事件是否令父view拦截到当前的触摸事件流.
* Check if this event as provided to the parent view's onInterceptTouchEvent should
* cause the parent to intercept the touch event stream.
*
* @param ev MotionEvent provided to onInterceptTouchEvent - 提供给onInterceptTouchEvent()方法的触摸事件对象
* @return true if the parent view should return true from onInterceptTouchEvent
*/
public boolean shouldInterceptTouchEvent(MotionEvent ev) {
final int action = MotionEventCompat.getActionMasked(ev);
final int actionIndex = MotionEventCompat.getActionIndex(ev);
if (action == MotionEvent.ACTION_DOWN) {
// Reset things for a new event stream, just in case we didn't get
// the whole previous stream.
cancel();
}
if (mVelocityTracker == null) {
mVelocityTracker = VelocityTracker.obtain();
}
mVelocityTracker.addMovement(ev);
switch (action) {
case MotionEvent.ACTION_DOWN: {
final float x = ev.getX();
final float y = ev.getY();
final int pointerId = MotionEventCompat.getPointerId(ev, 0);
saveInitialMotion(x, y, pointerId);
final View toCapture = findTopChildUnder((int) x, (int) y);
// Catch a settling view if possible.
if (toCapture == mCapturedView && mDragState == STATE_SETTLING) {
tryCaptureViewForDrag(toCapture, pointerId);
}
final int edgesTouched = mInitialEdgesTouched[pointerId];
if ((edgesTouched & mTrackingEdges) != 0) {
mCallback.onEdgeTouched(edgesTouched & mTrackingEdges, pointerId);
}
break;
}
case MotionEventCompat.ACTION_POINTER_DOWN: {
final int pointerId = MotionEventCompat.getPointerId(ev, actionIndex);
final float x = MotionEventCompat.getX(ev, actionIndex);
final float y = MotionEventCompat.getY(ev, actionIndex);
saveInitialMotion(x, y, pointerId);
// A ViewDragHelper can only manipulate one view at a time.
if (mDragState == STATE_IDLE) {
final int edgesTouched = mInitialEdgesTouched[pointerId];
if ((edgesTouched & mTrackingEdges) != 0) {
mCallback.onEdgeTouched(edgesTouched & mTrackingEdges, pointerId);
}
} else if (mDragState == STATE_SETTLING) {
// Catch a settling view if possible.
final View toCapture = findTopChildUnder((int) x, (int) y);
if (toCapture == mCapturedView) {
tryCaptureViewForDrag(toCapture, pointerId);
}
}
break;
}
case MotionEvent.ACTION_MOVE: {
// First to cross a touch slop over a draggable view wins. Also report edge drags.
final int pointerCount = MotionEventCompat.getPointerCount(ev);
for (int i = 0; i < pointerCount; i++) {
final int pointerId = MotionEventCompat.getPointerId(ev, i);
final float x = MotionEventCompat.getX(ev, i);
final float y = MotionEventCompat.getY(ev, i);
final float dx = x - mInitialMotionX[pointerId];
final float dy = y - mInitialMotionY[pointerId];
final View toCapture = findTopChildUnder((int) x, (int) y);
final boolean pastSlop = toCapture != null && checkTouchSlop(toCapture, dx, dy);
if (pastSlop) {
// check the callback's
// getView[Horizontal|Vertical]DragRange methods to know
// if you can move at all along an axis, then see if it
// would clamp to the same value. If you can't move at
// all in every dimension with a nonzero range, bail.
final int oldLeft = toCapture.getLeft();
final int targetLeft = oldLeft + (int) dx;
final int newLeft = mCallback.clampViewPositionHorizontal(toCapture,
targetLeft, (int) dx);
final int oldTop = toCapture.getTop();
final int targetTop = oldTop + (int) dy;
final int newTop = mCallback.clampViewPositionVertical(toCapture, targetTop,
(int) dy);
final int horizontalDragRange = mCallback.getViewHorizontalDragRange(
toCapture);
final int verticalDragRange = mCallback.getViewVerticalDragRange(toCapture);
if ((horizontalDragRange == 0 || horizontalDragRange > 0
&& newLeft == oldLeft) && (verticalDragRange == 0
|| verticalDragRange > 0 && newTop == oldTop)) {
break;
}
}
reportNewEdgeDrags(dx, dy, pointerId);
if (mDragState == STATE_DRAGGING) {
// Callback might have started an edge drag
break;
}
if (pastSlop && tryCaptureViewForDrag(toCapture, pointerId)) {
break;
}
}
saveLastMotion(ev);
break;
}
case MotionEventCompat.ACTION_POINTER_UP: {
final int pointerId = MotionEventCompat.getPointerId(ev, actionIndex);
clearMotionHistory(pointerId);
break;
}
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_CANCEL: {
cancel();
break;
}
}
return mDragState == STATE_DRAGGING;
}
/**
* 加工从父view中获取的触摸事件.这个方法将分发callback回调事件.父view的触摸事件实现中应该调用该方法.
* Process a touch event received by the parent view. This method will dispatch callback events
* as needed before returning. The parent view's onTouchEvent implementation should call this.
*
* @param ev The touch event received by the parent view
*/
public void processTouchEvent(MotionEvent ev) {
final int action = MotionEventCompat.getActionMasked(ev);
final int actionIndex = MotionEventCompat.getActionIndex(ev);
if (action == MotionEvent.ACTION_DOWN) {
// Reset things for a new event stream, just in case we didn't get
// the whole previous stream.
cancel();
}
if (mVelocityTracker == null) {
mVelocityTracker = VelocityTracker.obtain();
}
mVelocityTracker.addMovement(ev);
switch (action) {
case MotionEvent.ACTION_DOWN: {
final float x = ev.getX();
final float y = ev.getY();
final int pointerId = MotionEventCompat.getPointerId(ev, 0);
final View toCapture = findTopChildUnder((int) x, (int) y);
saveInitialMotion(x, y, pointerId);
// Since the parent is already directly processing this touch event,
// there is no reason to delay for a slop before dragging.
// Start immediately if possible.
tryCaptureViewForDrag(toCapture, pointerId);
final int edgesTouched = mInitialEdgesTouched[pointerId];
if ((edgesTouched & mTrackingEdges) != 0) {
mCallback.onEdgeTouched(edgesTouched & mTrackingEdges, pointerId);
}
break;
}
case MotionEventCompat.ACTION_POINTER_DOWN: {
final int pointerId = MotionEventCompat.getPointerId(ev, actionIndex);
final float x = MotionEventCompat.getX(ev, actionIndex);
final float y = MotionEventCompat.getY(ev, actionIndex);
saveInitialMotion(x, y, pointerId);
// A ViewDragHelper can only manipulate one view at a time.
if (mDragState == STATE_IDLE) {
// If we're idle we can do anything! Treat it like a normal down event.
final View toCapture = findTopChildUnder((int) x, (int) y);
tryCaptureViewForDrag(toCapture, pointerId);
final int edgesTouched = mInitialEdgesTouched[pointerId];
if ((edgesTouched & mTrackingEdges) != 0) {
mCallback.onEdgeTouched(edgesTouched & mTrackingEdges, pointerId);
}
} else if (isCapturedViewUnder((int) x, (int) y)) {
// We're still tracking a captured view. If the same view is under this
// point, we'll swap to controlling it with this pointer instead.
// (This will still work if we're "catching" a settling view.)
tryCaptureViewForDrag(mCapturedView, pointerId);
}
break;
}
case MotionEvent.ACTION_MOVE: {
if (mDragState == STATE_DRAGGING) {
final int index = MotionEventCompat.findPointerIndex(ev, mActivePointerId);
final float x = MotionEventCompat.getX(ev, index);
final float y = MotionEventCompat.getY(ev, index);
final int idx = (int) (x - mLastMotionX[mActivePointerId]);
final int idy = (int) (y - mLastMotionY[mActivePointerId]);
dragTo(mCapturedView.getLeft() + idx, mCapturedView.getTop() + idy, idx, idy);
saveLastMotion(ev);
} else {
// Check to see if any pointer is now over a draggable view.
final int pointerCount = MotionEventCompat.getPointerCount(ev);
for (int i = 0; i < pointerCount; i++) {
final int pointerId = MotionEventCompat.getPointerId(ev, i);
final float x = MotionEventCompat.getX(ev, i);
final float y = MotionEventCompat.getY(ev, i);
final float dx = x - mInitialMotionX[pointerId];
final float dy = y - mInitialMotionY[pointerId];
reportNewEdgeDrags(dx, dy, pointerId);
if (mDragState == STATE_DRAGGING) {
// Callback might have started an edge drag.
break;
}
final View toCapture = findTopChildUnder((int) x, (int) y);
if (checkTouchSlop(toCapture, dx, dy) &&
tryCaptureViewForDrag(toCapture, pointerId)) {
break;
}
}
saveLastMotion(ev);
}
break;
}
case MotionEventCompat.ACTION_POINTER_UP: {
final int pointerId = MotionEventCompat.getPointerId(ev, actionIndex);
if (mDragState == STATE_DRAGGING && pointerId == mActivePointerId) {
// Try to find another pointer that's still holding on to the captured view.
int newActivePointer = INVALID_POINTER;
final int pointerCount = MotionEventCompat.getPointerCount(ev);
for (int i = 0; i < pointerCount; i++) {
final int id = MotionEventCompat.getPointerId(ev, i);
if (id == mActivePointerId) {
// This one's going away, skip.
continue;
}
final float x = MotionEventCompat.getX(ev, i);
final float y = MotionEventCompat.getY(ev, i);
if (findTopChildUnder((int) x, (int) y) == mCapturedView &&
tryCaptureViewForDrag(mCapturedView, id)) {
newActivePointer = mActivePointerId;
break;
}
}
if (newActivePointer == INVALID_POINTER) {
// We didn't find another pointer still touching the view, release it.
releaseViewForPointerUp();
}
}
clearMotionHistory(pointerId);
break;
}
case MotionEvent.ACTION_UP: {
if (mDragState == STATE_DRAGGING) {
releaseViewForPointerUp();
}
cancel();
break;
}
case MotionEvent.ACTION_CANCEL: {
if (mDragState == STATE_DRAGGING) {
dispatchViewReleased(0, 0);
}
cancel();
break;
}
}
}
//更新边缘拖曳标记
private void reportNewEdgeDrags(float dx, float dy, int pointerId) {
int dragsStarted = 0;
if (checkNewEdgeDrag(dx, dy, pointerId, EDGE_LEFT)) {
dragsStarted |= EDGE_LEFT;
}
if (checkNewEdgeDrag(dy, dx, pointerId, EDGE_TOP)) {
dragsStarted |= EDGE_TOP;
}
if (checkNewEdgeDrag(dx, dy, pointerId, EDGE_RIGHT)) {
dragsStarted |= EDGE_RIGHT;
}
if (checkNewEdgeDrag(dy, dx, pointerId, EDGE_BOTTOM)) {
dragsStarted |= EDGE_BOTTOM;
}
if (dragsStarted != 0) {
mEdgeDragsInProgress[pointerId] |= dragsStarted;
mCallback.onEdgeDragStarted(dragsStarted, pointerId);
}
}
//内部调用方法,计算是否新的拖曳标记
private boolean checkNewEdgeDrag(float delta, float odelta, int pointerId, int edge) {
final float absDelta = Math.abs(delta);
final float absODelta = Math.abs(odelta);
if ((mInitialEdgesTouched[pointerId] & edge) != edge || (mTrackingEdges & edge) == 0 ||
(mEdgeDragsLocked[pointerId] & edge) == edge ||
(mEdgeDragsInProgress[pointerId] & edge) == edge ||
(absDelta <= mTouchSlop && absODelta <= mTouchSlop)) {
return false;
}
if (absDelta < absODelta * 0.5f && mCallback.onEdgeLock(edge)) {
mEdgeDragsLocked[pointerId] |= edge;
return false;
}
return (mEdgeDragsInProgress[pointerId] & edge) == 0 && absDelta > mTouchSlop;
}
/**
* 检测在子view滑动时是否合理的出现溢出(这个现象是手指在滑动时部分滑动到屏幕外,但子view还能正常被拖曳移动).
* 当溢出现象严重,子view就不能沿着手指滑动的轨迹在水平或垂直轴上被拖曳移动.这时,该轴上的手势将不计入检测溢出的考虑范围.
*
* Check if we've crossed a reasonable touch slop for the given child view.
* If the child cannot be dragged along the horizontal or vertical axis, motion
* along that axis will not count toward the slop check.
*
* @param child Child to check - 要检测的子view
* @param dx Motion since initial position along X axis - 从初始开始沿着X轴的坐标
* @param dy Motion since initial position along Y axis - - 从初始开始沿着Y的坐标
* @return true if the touch slop has been crossed
*/
private boolean checkTouchSlop(View child, float dx, float dy) {
if (child == null) {
return false;
}
final boolean checkHorizontal = mCallback.getViewHorizontalDragRange(child) > 0;
final boolean checkVertical = mCallback.getViewVerticalDragRange(child) > 0;
if (checkHorizontal && checkVertical) {
return dx * dx + dy * dy > mTouchSlop * mTouchSlop;
} else if (checkHorizontal) {
return Math.abs(dx) > mTouchSlop;
} else if (checkVertical) {
return Math.abs(dy) > mTouchSlop;
}
return false;
}
/**
* 检测当前手势是否的点是否超出了溢出的临界值.
*
* Check if any pointer tracked in the current gesture has crossed
* the required slop threshold.
*
* 这依赖于由方法shouldInterceptTouchEvent(...)或者processTouchEvent(...)所填充的内部状态.
* 你只有在所有有效触摸的数据都被提供到这其中的一个方法时,才应该去使用这些方法返回的结果.
*
* <p>This depends on internal state populated by
* {@link #shouldInterceptTouchEvent(android.view.MotionEvent)} or
* {@link #processTouchEvent(android.view.MotionEvent)}. You should only rely on
* the results of this method after all currently available touch data
* has been provided to one of these two methods.</p>
*
* 参数directions - 指引值. 值为{@link #DIRECTION_HORIZONTAL},
* {@link #DIRECTION_VERTICAL}, {@link #DIRECTION_ALL}中的其中一个.
* @param directions Combination of direction flags, see {@link #DIRECTION_HORIZONTAL},
* {@link #DIRECTION_VERTICAL}, {@link #DIRECTION_ALL}
*
* 如果返回true,表示超过了溢出的临界值.否则返回false.
* @return true if the slop threshold has been crossed, false otherwise
*/
public boolean checkTouchSlop(int directions) {
final int count = mInitialMotionX.length;
//mInitialMotionX装着触摸事件的所有坐标(所有pointer),因此循环去检验,只要有一个点超出临界值,就返回true.
for (int i = 0; i < count; i++) {
if (checkTouchSlop(directions, i)) {
return true;
}
}
return false;
}
/**
* 检测越出所需的溢出临界值的手势中,某个被追踪的具体的pointer.
*
* Check if the specified pointer tracked in the current gesture has crossed
* the required slop threshold.
*
* 这依赖于由方法shouldInterceptTouchEvent(...)或者processTouchEvent(...)所填充的内部状态.
* 你只有在所有有效触摸的数据都被提供到这其中的一个方法时,才应该去使用这些方法返回的结果.
*
* <p>This depends on internal state populated by
* {@link #shouldInterceptTouchEvent(android.view.MotionEvent)} or
* {@link #processTouchEvent(android.view.MotionEvent)}. You should only rely on
* the results of this method after all currently available touch data
* has been provided to one of these two methods.</p>
*
* 下面参数directions的解释跟上一个方法checkTouchSlop()是一样的.
* @param directions Combination of direction flags, see {@link #DIRECTION_HORIZONTAL},
* {@link #DIRECTION_VERTICAL}, {@link #DIRECTION_ALL}
* @param pointerId ID of the pointer to slop check as specified by MotionEvent
* @return true if the slop threshold has been crossed, false otherwise
*/
public boolean checkTouchSlop(int directions, int pointerId) {
if (!isPointerDown(pointerId)) {
return false;
}
final boolean checkHorizontal = (directions & DIRECTION_HORIZONTAL) == DIRECTION_HORIZONTAL;
final boolean checkVertical = (directions & DIRECTION_VERTICAL) == DIRECTION_VERTICAL;
final float dx = mLastMotionX[pointerId] - mInitialMotionX[pointerId];
final float dy = mLastMotionY[pointerId] - mInitialMotionY[pointerId];
if (checkHorizontal && checkVertical) {
//如果是同时水平和垂直的运动,就检测X和Y轴坐标的平方的和.(直角三角形,两条直角边的平方的和等于第三边的平方.)
return dx * dx + dy * dy > mTouchSlop * mTouchSlop;
} else if (checkHorizontal) {
//mTouchSlop是临界值, 如果dx的绝对值大于这个值,表示已超出临界值,返回true,否则返回false.
return Math.abs(dx) > mTouchSlop;
} else if (checkVertical) {
//同前面一个解释.
return Math.abs(dy) > mTouchSlop;
}
return false;
}
/**
* 检测在当前活动的手势中一开始触摸时的屏幕边缘.如果没有活动的手势,该方法会返回false.
*
* Check if any of the edges specified were initially touched in the currently active gesture.
* If there is no currently active gesture this method will return false.
*
* 参数edges - 所检测的边缘
*
* @param edges Edges to check for an initial edge touch. See {@link #EDGE_LEFT},
* {@link #EDGE_TOP}, {@link #EDGE_RIGHT}, {@link #EDGE_BOTTOM} and
* {@link #EDGE_ALL}
* @return true if any of the edges specified were initially touched in the current gesture
*/
public boolean isEdgeTouched(int edges) {
final int count = mInitialEdgesTouched.length;
for (int i = 0; i < count; i++) {
if (isEdgeTouched(edges, i)) {
return true;
}
}
return false;
}
/**
* 用于检测边缘中某个有具体ID值的poniter(点).
* (如果到这里还没有搞懂pointer和触摸或者和drag之间到底有什么关系,不妨这么
* 想象,一个触摸屏幕的手势是由一定数量的点去组成的,而每一个这样的点,就是一个pointer.手指一触碰屏幕,肯定会产生至少一个
* pointer.)
* 如果当前没有活动的手势,或者给定的pointerId并没有对应的pointer,那么该方法会返回false.否则返回true.
*
* Check if any of the edges specified were initially touched by the pointer with
* the specified ID. If there is no currently active gesture or if there is no pointer with
* the given ID currently down this method will return false.
*
* 参数edges - 该值是EDGE_LEFT, EDGE_TOP, EDGE_RIGHT, EDGE_RIGHT和EDGE_RIGHT中的其中一个.
* 很显然,屏幕只有左上右下这四个边缘.
* @param edges Edges to check for an initial edge touch. See {@link #EDGE_LEFT},
* {@link #EDGE_TOP}, {@link #EDGE_RIGHT}, {@link #EDGE_RIGHT} and
* {@link #EDGE_ALL}
* @return true if any of the edges specified were initially touched in the current gesture
*/
public boolean isEdgeTouched(int edges, int pointerId) {
return isPointerDown(pointerId) && (mInitialEdgesTouched[pointerId] & edges) != 0;
}
//跟dispatchViewReleased(...)方法是类似的,当pointer消失时回收view.
private void releaseViewForPointerUp() {
//computeCurrentVelocity()方法是根据当前收集到的pointer去计算速度
mVelocityTracker.computeCurrentVelocity(1000, mMaxVelocity);
final float xvel = clampMag(
VelocityTrackerCompat.getXVelocity(mVelocityTracker, mActivePointerId),
mMinVelocity, mMaxVelocity);
final float yvel = clampMag(
VelocityTrackerCompat.getYVelocity(mVelocityTracker, mActivePointerId),
mMinVelocity, mMaxVelocity);
dispatchViewReleased(xvel, yvel);
}
//拖曳的方法
private void dragTo(int left, int top, int dx, int dy) {
int clampedX = left;
int clampedY = top;
final int oldLeft = mCapturedView.getLeft();
final int oldTop = mCapturedView.getTop();
if (dx != 0) {
clampedX = mCallback.clampViewPositionHorizontal(mCapturedView, left, dx);
//设置水平偏移值
mCapturedView.offsetLeftAndRight(clampedX - oldLeft);
}
if (dy != 0) {
clampedY = mCallback.clampViewPositionVertical(mCapturedView, top, dy);
//设置垂直偏移值
mCapturedView.offsetTopAndBottom(clampedY - oldTop);
}
if (dx != 0 || dy != 0) {
final int clampedDx = clampedX - oldLeft;
final int clampedDy = clampedY - oldTop;
//既然拖曳肯定发送位置变更,就回调该接口方法
mCallback.onViewPositionChanged(mCapturedView, clampedX, clampedY,
clampedDx, clampedDy);
}
}
/**
* 获取当前捕获的view是否在父view的坐标系统的某个点之下.如果不存在捕获的view,该方法返回false.
* (实则,这个方法可获知,触摸的点,捕获的view以及该view所在的父view是否同时处于一个坐标系统.如果是,
* 这才是一个有效的触摸拖曳事件.)
*
* Determine if the currently captured view is under the given point in the
* parent view's coordinate system. If there is no captured view this method
* will return false.
*
* @param x X position to test in the parent's coordinate system - 父view坐标系统的X轴坐标
* @param y Y position to test in the parent's coordinate system - 父view坐标系统的Y轴坐标
* @return true if the captured view is under the given point, false otherwise
*/
public boolean isCapturedViewUnder(int x, int y) {
return isViewUnder(mCapturedView, x, y);
}
/**
* (该方法在上面被调用,也可以外部调用.)
* 某个view是否在父view给定的点(所处的坐标系统)之下.意思跟上一个方法isCapturedViewUnder(...)是一样的.
*
* Determine if the supplied view is under the given point in the
* parent view's coordinate system.
*
* @param view Child view of the parent to hit test - 父view中所要测试的子view对象
* @param x X position to test in the parent's coordinate system - 父view中坐标系统的X轴坐标
* @param y Y position to test in the parent's coordinate system - 父view中坐标系统的Y轴坐标
* @return true if the supplied view is under the given point, false otherwise
*/
public boolean isViewUnder(View view, int x, int y) {
if (view == null) {
return false;
}
//显然,当X,Y所定位的点同时在子view内时才返回true.
return x >= view.getLeft() &&
x < view.getRight() &&
y >= view.getTop() &&
y < view.getBottom();
}
/**
* 找出父view坐标系统中指定点所定位的最顶层的子view.
* (这里需要点空间想象力,除了X,Y轴还存在Z轴,Z轴同时垂直X,Y轴.)父view中最顶层的子view,自然能就是Z轴中队对应
* 的Z值最大的子view.这种排列方法参考方法{@link Callback#getOrderedChildIndex(int)}.
* (其实我们无需过多关心这个Z轴,如果在布局文件XML中,我们只需要保证添加Drag事件的子view处于父view的顶层可见即可.)
*
* Find the topmost child under the given point within the parent view's coordinate system.
* The child order is determined using {@link Callback#getOrderedChildIndex(int)}.
*
* @param x X position to test in the parent's coordinate system - 父view坐标系统的X轴坐标
* @param y Y position to test in the parent's coordinate system - 父view坐标系统的Y轴坐标
* @return The topmost child view under (x, y) or null if none found. - 如果没找到这个最顶层子view则返回null.
*/
public View findTopChildUnder(int x, int y) {
final int childCount = mParentView.getChildCount();
//应该不难理解,直接从i最大的位置开始遍历,第一个就是最顶层.同时还要保证该point的X,Y值都在该子view之内.
for (int i = childCount - 1; i >= 0; i--) {
final View child = mParentView.getChildAt(mCallback.getOrderedChildIndex(i));
if (x >= child.getLeft() && x < child.getRight() &&
y >= child.getTop() && y < child.getBottom()) {
return child;
}
}
return null;
}
//获取边缘大小
private int getEdgesTouched(int x, int y) {
int result = 0;
// 因为子view是处于屏幕内,view的坐标轴原点是在左上角.向下为X轴正方形,向右为Y轴正方向.
// 因此,左侧和顶部都需要加mEdgeSize,而底部和右侧则是减去mEdgeSize,如果X或者Y轴坐标处于加上或减去mEdgeSize
// 的范围内,则对result和诸如EDGE_LEFT这样的值进行按位或运算,然后赋值给result再返回.
// 结合上面整个类,到了这里不禁要想为何这里和前面的一些方法都进行按位运算,好简单的理由呵呵:
// 因为EDGE_LEFT,EDGE_TOP等这些值本身就是二进制取值的.
if (x < mParentView.getLeft() + mEdgeSize) result |= EDGE_LEFT;
if (y < mParentView.getTop() + mEdgeSize) result |= EDGE_TOP;
if (x > mParentView.getRight() - mEdgeSize) result |= EDGE_RIGHT;
if (y > mParentView.getBottom() - mEdgeSize) result |= EDGE_BOTTOM;
return result;
}
}
原文地址：http://blog.csdn.net/stzy00/article/details/45512003
