史上最全的Android ViewDragHelper解析

简介： 一般我们在自定义ViewGroup 的时候会通常都会用到onInterceptTouchEvent ，onTouchEvent 这些方法去进行距离的判断然后利用scroller 去进行目标的移动，从而实现ViewGroup 的自定义。此方法不但判断麻烦，而且逻辑复杂，不易操作，今天给大家要价讲的这个工具ViewDragHelper 是谷歌IO大会上推出的触摸辅助开发工具，极大的简化了开发自定义VIewGroup 的难度。

1.废话不多说 ，首先要初始化 ViewDragHelper 这个工具类：

  final float density = getResources().getDisplayMetrics().density;
        final float minVel = MIN_FLING_VELOCITY * density;
        //指定好需要处理拖动的ViewGroup和回调 就可以开始使用了
        mViewDragHelper = ViewDragHelper.create(this, new DefaultDragHelper());
        mViewDragHelper.setEdgeTrackingEnabled(ViewDragHelper.EDGE_LEFT);
        //设置minVelocity
        mViewDragHelper.setMinVelocity(minVel);

2.初始化 ViewDragHelper.Callback 这个触摸操作类：并初始化 要操作VIew的位置控制方法回掉类：

onViewPositionChanged（）
        @Override
        public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {
            super.onViewPositionChanged(changedView, left, top, dx, dy);

            mLeft = left;
            mLeftSize =(-left)/ (dip2px(getContext(),80) * 1.0f);
            Log.d(TAG, "onViewPositionChanged()--" + "left:" + left + ",top:" + top + ",dx:" + dx + ",dy:" + dy + "mLeftSize--" + mLeftSize);
            invalidate();
        }

3.接下来我们会操作要移动VIew 的滑动限制距离 方法：

  /**
         * 限制子View水平拖拉操作。默认不支持水平操作，重写该方法提供新的水平坐标（根据提供的渴望的水平坐标）
         * 不重写就不会支持水平坐标变化
         *
         * @param child Child view being dragged
         * @param left  Attempted motion along the X axis
         * @param dx    Proposed change in position for left
         * @return The new clamped position for left
         */
        @Override
        public int clampViewPositionHorizontal(View child, int left, int dx) {
            final int leftBound =v_content.getPaddingLeft()-dip2px(getContext(),80);
            final int rightBound =v_content.getPaddingRight();
            final int newLeft = Math.min(Math.max(left, leftBound), rightBound);
            Log.d(TAG, "clampViewPositionHorizontal()--left:" + left + ",dx:" + dx+"v_content.getPaddingLeft(),"+v_content.getPaddingLeft());
            return newLeft;
        }
    }

1. 限制View活动的范围后 ，但我们释放手指的时候我们会操作另外一个方法:

    /**
         * 手指离开屏幕
         * 后续View 的坐标处理
         * 比如  滑到超过一半 直接滑到满屏 又或者滑到不到一半的时候
         * 还原坐标
         *
         * @param releasedChild
         * @param xvel
         * @param yvel
        * */
        @Override
        public void onViewReleased(View releasedChild, float xvel, float yvel) {
            super.onViewReleased(releasedChild, xvel, yvel);
            Log.d(TAG, "onViewReleased()--xv:" + xvel + ",yv:" + yvel);
            //上拉
            if (mLeftSize > 0.5) {
                openCover();
            } else {
                closeCover();
            }
            invalidate();
        }

这样一个基本的VIew滑动类就基本实现了。
接下来我贴出一个完整的示例：

 package com.example.administrator.myapplication.fragment;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Toast;

import com.example.administrator.myapplication.R;
import com.example.administrator.myapplication.widget.BotomDragLayout;
import com.example.administrator.myapplication.widget.LeftScrollDeleteDragLayout;

/**
 * 侧滑删除列表
 * 2016/4/21
 * gxj
 */
public class LeftScrollDeleteLayoutFragment extends Fragment {
    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        getActivity().setTitle("LeftScrollDeleteLayoutFragment");
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        final LeftScrollDeleteDragLayout view = (LeftScrollDeleteDragLayout) inflater.inflate(R.layout.left_scroll_delete_layout, container, false);
        View view_bg =view.findViewById(R.id.del);
        view_bg.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(view.STATE == BotomDragLayout.CLOSEING){
                    view.openCover();
                }else{
                    view.closeCover();
                    Toast.makeText(getActivity(),"删除",Toast.LENGTH_SHORT).show();
                }
            }
        });
        return view;
    }

}

所需要的xml布局：

<com.example.administrator.myapplication.widget.LeftScrollDeleteDragLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@android:color/white">
        <LinearLayout
            android:id="@+id/view_bg"
            android:layout_width="match_parent"
            android:layout_height="200dp"
            android:orientation="horizontal"
            android:gravity="right">
                <Button
                    android:id="@+id/del"
                    android:layout_width="80dp"
                    android:layout_height="match_parent"
                    android:text="删除"
                    android:textColor="@color/white"
                    android:background="@color/red"
                    android:gravity="center"
                    />
        </LinearLayout>
        <Button
            android:id="@+id/view_content"
            android:layout_width="match_parent"
            android:layout_height="200dp"
            android:text="向左滑出删除按钮"
            android:gravity="center"
            android:background="@color/colorPrimary"
            android:textColor="@android:color/white"
            />
</com.example.administrator.myapplication.widget.LeftScrollDeleteDragLayout>

完整的自定义侧滑类代码：

package com.example.administrator.myapplication.widget;
import android.content.Context;
import android.support.v4.view.MotionEventCompat;
import android.support.v4.widget.ViewDragHelper;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;

import com.example.administrator.myapplication.R;

/**
 *列表侧滑删除效果
 * author gxj
 * date 2016.5.22
 */
public class LeftScrollDeleteDragLayout extends ViewGroup {
    private final String TAG = this.getClass().getSimpleName();
    private ViewDragHelper mViewDragHelper;
    /**
     * Minimum velocity that will be detected as a fling
     */
    private static final int MIN_FLING_VELOCITY = 400; // dips per second
    /**
     * 菜单栏的状态
     */
    public  int STATE = 0;
    public static final int CLOSEING = 0;
    public static final int OPENED = 1;
    private View v_content;
    private int viewWidth = 0;
    /**
     * 滑动view 的顶部位置
     */
    private int mLeft;
    /**
     * 滑动view 的滑动距离占自身高度的比例
     */
    private float mLeftSize;
    private View view_bg;

    public LeftScrollDeleteDragLayout(Context context) {
        this(context, null);
        init();
    }

    public LeftScrollDeleteDragLayout(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
        init();
    }

    public LeftScrollDeleteDragLayout(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        v_content = findViewById(R.id.view_content);
        view_bg = findViewById(R.id.view_bg);
        viewWidth = v_content.getHeight();
    }

    @Override
    public void computeScroll() {
        if (mViewDragHelper.continueSettling(true)) {
            postInvalidateOnAnimation();
        }
    }

    public void openCover() {
        STATE = LeftScrollDeleteDragLayout.OPENED;
        mViewDragHelper.smoothSlideViewTo(v_content, -dip2px(getContext(),80), 0);
        postInvalidateOnAnimation();
    }

    public void closeCover() {
        STATE = LeftScrollDeleteDragLayout.CLOSEING;
        mViewDragHelper.smoothSlideViewTo(v_content, 0, 0);
        postInvalidateOnAnimation();
    }

    private void init() {
        final float density = getResources().getDisplayMetrics().density;
        final float minVel = MIN_FLING_VELOCITY * density;
        //指定好需要处理拖动的ViewGroup和回调 就可以开始使用了
        mViewDragHelper = ViewDragHelper.create(this, new DefaultDragHelper());
        mViewDragHelper.setEdgeTrackingEnabled(ViewDragHelper.EDGE_LEFT);
        //设置minVelocity
        mViewDragHelper.setMinVelocity(minVel);
    }

    private class DefaultDragHelper extends ViewDragHelper.Callback {
        @Override
        public boolean tryCaptureView(View view, int i) {
            return view == v_content;
        }

        @Override
        public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {
            super.onViewPositionChanged(changedView, left, top, dx, dy);

            mLeft = left;
            mLeftSize =(-left)/ (dip2px(getContext(),80) * 1.0f);
            Log.d(TAG, "onViewPositionChanged()--" + "left:" + left + ",top:" + top + ",dx:" + dx + ",dy:" + dy + "mLeftSize--" + mLeftSize);
            invalidate();
        }

        /**
         * 当captureview被捕获时回调
         *
         * @param capturedChild
         * @param activePointerId
         */
        @Override
        public void onViewCaptured(View capturedChild, int activePointerId) {
            super.onViewCaptured(capturedChild, activePointerId);
            Log.d(TAG, "onViewCaptured()--:");
        }

        /**
         * 手指离开屏幕
         * 后续View 的坐标处理
         * 比如  滑到超过一半 直接滑到满屏 又或者滑到不到一半的时候
         * 还原坐标
         *
         * @param releasedChild
         * @param xvel
         * @param yvel
         */
        @Override
        public void onViewReleased(View releasedChild, float xvel, float yvel) {
            super.onViewReleased(releasedChild, xvel, yvel);
            Log.d(TAG, "onViewReleased()--xv:" + xvel + ",yv:" + yvel);
            //上拉
            if (mLeftSize > 0.5) {
                openCover();
            } else {
                closeCover();
            }
            invalidate();
        }

        /**
         * 当触摸到边缘的时候会调用
         * @param edgeFlags
         * @param pointerId
         */
        @Override
        public void onEdgeTouched(int edgeFlags, int pointerId) {
            super.onEdgeTouched(edgeFlags, pointerId);
            Log.d(TAG, "onEdgeTouched()");
        }

        @Override
        public boolean onEdgeLock(int edgeFlags) {
            Log.d(TAG, "onEdgeLock()");
            return super.onEdgeLock(edgeFlags);
        }

        /**
         * 当触摸到边缘的时候会调用
         *
         * @param edgeFlags
         * @param pointerId 可以指定触摸边缘的子View
         */
        @Override
        public void onEdgeDragStarted(int edgeFlags, int pointerId) {
            super.onEdgeDragStarted(edgeFlags, pointerId);
            Log.d(TAG, "onEdgeDragStarted()");
            mViewDragHelper.captureChildView(v_content, pointerId);
        }

        /**
         * 返回当前移动的View 的position
         *
         * @param index
         * @return
         */
        @Override
        public int getOrderedChildIndex(int index) {
            return super.getOrderedChildIndex(index);
        }

        /**
         * 限制水平移动范围
         * Return the magnitude of a draggable child view‘s horizontal range of motion in pixels.
         * 似乎作用不大，其他情况只用于判断是否可以拖动
         * 具体返回值真正起作用在于{@link ViewDragHelper#smoothSlideViewTo(View, int, int)}
         *
         * @param child Child view to check
         * @return range of horizontal motion in pixels
         */
        @Override
        public int getViewHorizontalDragRange(View child) {
            return child ==v_content?dip2px(getContext(),80):0;
        }


        /**
         * 限制子View水平拖拉操作。默认不支持水平操作，重写该方法提供新的水平坐标（根据提供的渴望的水平坐标）
         * 不重写就不会支持水平坐标变化
         *
         * @param child Child view being dragged
         * @param left  Attempted motion along the X axis
         * @param dx    Proposed change in position for left
         * @return The new clamped position for left
         */
        @Override
        public int clampViewPositionHorizontal(View child, int left, int dx) {
            final int leftBound =v_content.getPaddingLeft()-dip2px(getContext(),80);
            final int rightBound =v_content.getPaddingRight();
            final int newLeft = Math.min(Math.max(left, leftBound), rightBound);
            Log.d(TAG, "clampViewPositionHorizontal()--left:" + left + ",dx:" + dx+"v_content.getPaddingLeft(),"+v_content.getPaddingLeft());
            return newLeft;
        }
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent event) {
        final int action = MotionEventCompat.getActionMasked(event);
        if (action == MotionEvent.ACTION_CANCEL || action == MotionEvent.ACTION_UP) {
            mViewDragHelper.cancel();
            return false;
        }
        //通过这个方法判断是否拦截 滑动事件
        boolean flag = mViewDragHelper.shouldInterceptTouchEvent(event);
        return flag;
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        //通过这个方法判断是否处理拦截的触摸事件
        mViewDragHelper.processTouchEvent(event);
        return true;
    }

    /**
     * 丈量所有控件的高度
     * 可以得到每个控件的最终高度
     * @param widthMeasureSpec
     * @param heightMeasureSpec
     */
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        measureChildren(widthMeasureSpec, heightMeasureSpec);
        int maxWidth = MeasureSpec.getSize(widthMeasureSpec);
        int maxHeight = MeasureSpec.getSize(heightMeasureSpec);
        setMeasuredDimension(resolveSizeAndState(maxWidth, widthMeasureSpec, 0),
                resolveSizeAndState(maxHeight, heightMeasureSpec, 0));
        viewWidth = v_content.getMeasuredWidth();
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        Log.e("onLayout", l + "|" + t + "|" + r + "|" + b);
        v_content.layout(mLeft, t, mLeft+viewWidth,dip2px(getContext(),200) );
        view_bg.layout(0, 0, r, dip2px(getContext(),200));
    }
    /**
     * 根据手机的分辨率从 dp 的单位 转成为 px(像素)
     */
    private  int dip2px(Context context, float dpValue) {
        final float scale = context.getResources().getDisplayMetrics().density;
        return (int) (dpValue * scale + 0.5f);
    }
}

最后附上demo的下载地址 ： 猛戳这里–https://github.com/g1258624735/MyApplication2
5. 所有的代码已经全部上传，注释很详细，包你看懂，已经详细的不能在详细了，看不懂的可以板砖拍我。
6. 大家在看的过程 当中，如果有什么不懂得话可以发邮件给我 ，1258624735@qq.com
7. ps: 如果大家觉得文章对你有帮助：不妨大赏一下支持原创，你的支持是我最大的动力：