Android触控事件

触控事件
MotionEvent类：

    //单击触摸按下动作
   public static final int ACTION_DOWN             = 0;

    /**
     * Constant for {@link #getActionMasked}: A pressed gesture has finished, the
     * motion contains the final release location as well as any intermediate
     * points since the last down or move event.
     * 单击触摸离开动作
     */
    public static final int ACTION_UP               = 1;

    /**
     * Constant for {@link #getActionMasked}: A change has happened during a
     * press gesture (between {@link #ACTION_DOWN} and {@link #ACTION_UP}).
     * The motion contains the most recent point, as well as any intermediate
     * points since the last down or move event.
     * 触摸点移动动作
     */
    public static final int ACTION_MOVE             = 2;

    /**
     * Constant for {@link #getActionMasked}: The current gesture has been aborted.
     * You will not receive any more points in it.  You should treat this as
     * an up event, but not perform any action that you normally would.
     * 触摸动作取消
     */
    public static final int ACTION_CANCEL           = 3;

    /**
     * Constant for {@link #getActionMasked}: A movement has happened outside of the
     * normal bounds of the UI element.  This does not provide a full gesture,
     * but only the initial location of the movement/touch.
     * 触摸动作超出边界
     */
    public static final int ACTION_OUTSIDE          = 4;

    /**
     * Constant for {@link #getActionMasked}: A non-primary pointer has gone down.
     * <p>
     * Use {@link #getActionIndex} to retrieve the index of the pointer that changed.
     * </p><p>
     * The index is encoded in the {@link #ACTION_POINTER_INDEX_MASK} bits of the
     * unmasked action returned by {@link #getAction}.
     * </p>
     * 多点触摸按下动作
     */
    public static final int ACTION_POINTER_DOWN     = 5;

    /**
     * Constant for {@link #getActionMasked}: A non-primary pointer has gone up.
     * <p>
     * Use {@link #getActionIndex} to retrieve the index of the pointer that changed.
     * </p><p>
     * The index is encoded in the {@link #ACTION_POINTER_INDEX_MASK} bits of the
     * unmasked action returned by {@link #getAction}.
     * </p>
     * 多点离开动作
     */
    public static final int ACTION_POINTER_UP       = 6;

MotionEvent提供的方法：

getTop():获取到的是View自身的顶边到其父布局顶边的距离。
getLeft():获取到的是View自身的左边到其父布局左边的距离。
getRight():获取到的是View自身的右边到其父布局右边的距离。
getBottom():获取到的是View自身的底边到其父布局底边的距离。


getX():获取点击事件距离控件左边的距离
getY():获取点击事件距离控件顶边的距离
getRawX():获取点击事距离整个屏幕左边的距离，即绝对坐标。
getRawY():获取点击事距离整个屏幕顶边的距离，即绝对坐标。

**实现滑动的基本原理（核心思想）：
当触摸View时候，系统记录当前触摸点的坐标，当手指移动时候，系统记录下移动的触摸点坐标，从而获取到相对于前一次坐标点的偏移量，并且通过偏移量修改view的坐标，这样不断重复，从而实现滑动效果。**
实现滑动的常用方法：
layout方法：

package com.example.drawdemo;

import android.content.Context;
import android.graphics.Color;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class MyView5 extends View {
    private int lastX;
    private int lastY;

    public MyView5(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initView();
    }

    public MyView5(Context context, AttributeSet attrs) {
        super(context, attrs);
        initView();
    }

    public MyView5(Context context) {
        super(context);
        initView();
    }

    private void initView() {
        setBackgroundColor(Color.BLUE);
    }

    // 视图坐标方式
    public boolean onTouchEvent(MotionEvent event) {
        int x = (int) event.getX();
        int y = (int) event.getY();
        switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            lastX = x;
            lastY = y;
            break;
        case MotionEvent.ACTION_MOVE:
            // 计算偏移量
            int offsetX = x - lastX;
            int offsetY = y - lastY;
            layout(getLeft() + offsetX, getTop() + offsetY, getRight() + offsetX, getBottom() + offsetY);
            break;

        default:
            break;
        }

        return true;

    }
}

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.drawdemo.MainActivity" >


    <com.example.drawdemo.MyView5

        android:layout_width="100dp"
        android:layout_height="100dp" />

</RelativeLayout>

通过LayoutParams进行滑动。
LayoutParams 保存了一个View的布局参数，因此在程序中，通过改变LayoutParams修改一个布局的位置参数，从而达到改变View位置的效果。

而且我们可以使用getLayoutparams()来获取一个View的LayoutParams.计算偏移量的方法与在Layout方法中计算offset也是一样的，当获取偏移量后，就可以通过setLayoutParams来改变Layoutparams.

当然获取父容易布局，会有不同的布局（如果父容易是LinearLatyou，那么就要使用LinearLayout.LayoutParams.如果是RelativeLayout,那么就要使用RelativeLayout.LayoutParams.），所以我们直接使用ViewGroup.MarginLayoutParams来实现这个功能。

                    ViewGroup.MarginLayoutParams layoutParams = (ViewGroup.MarginLayoutParams) getLayoutParams();
// LinearLayout.LayoutParams layoutParams =(LinearLayout.LayoutParams) getLayoutParams();
                    layoutParams.leftMargin = getLeft() + offsetX;
                    layoutParams.topMargin = getTop() + offsetY;

这个使用更加方便，不用考录父容器布局。

package com.example.drawdemo;

import android.content.Context;
import android.graphics.Color;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;

public class MyView6 extends View {
    private int lastX;
    private int lastY;

    public MyView6(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        // TODO Auto-generated constructor stub
        ininView();
    }

    public MyView6(Context context, AttributeSet attrs) {
        super(context, attrs);
        ininView();
        // TODO Auto-generated constructor stub
    }

    public MyView6(Context context) {
        super(context);
        ininView();
        // TODO Auto-generated constructor stub
    }

    private void ininView() {
         setBackgroundColor(Color.GREEN);

    }
       @Override
        public boolean onTouchEvent(MotionEvent event) {
            int x = (int) event.getX();
            int y = (int) event.getY();
            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    // 记录触摸点坐标
                    lastX = (int) event.getX();
                    lastY = (int) event.getY();
                    break;
                case MotionEvent.ACTION_MOVE:
                    // 计算偏移量
                    int offsetX = x - lastX;
                    int offsetY = y - lastY;
                    ViewGroup.MarginLayoutParams layoutParams = (ViewGroup.MarginLayoutParams) getLayoutParams();
//                  LinearLayout.LayoutParams layoutParams = (LinearLayout.LayoutParams) getLayoutParams();
                    layoutParams.leftMargin = getLeft() + offsetX;
                    layoutParams.topMargin = getTop() + offsetY;
                    setLayoutParams(layoutParams);
                    break;
            }
            return true;
        }
}

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.drawdemo.MainActivity" >


    <com.example.drawdemo.MyView6
        android:layout_width="100dp"
        android:layout_height="100dp" />

</RelativeLayout>

通过scrollTo与scorllBy进行滑动。
android 系统提供这个两个方式进行改变一个View的位置
与前面的方法相同，也是计算偏移量。

package com.example.drawdemo;

import android.content.Context;
import android.graphics.Color;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class MyView7 extends View{


    private int lastX;
    private int lastY;

    public MyView7(Context context) {
        super(context);
        ininView();
    }

    public MyView7(Context context, AttributeSet attrs) {
        super(context, attrs);
        ininView();
    }

    public MyView7(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        ininView();
    }

    private void ininView() {
        setBackgroundColor(Color.YELLOW);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int x = (int) event.getX();
        int y = (int) event.getY();
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                lastX = (int) event.getX();
                lastY = (int) event.getY();
                break;
            case MotionEvent.ACTION_MOVE:
                int offsetX = x - lastX;
                int offsetY = y - lastY;
                ((View) getParent()).scrollBy(-offsetX, -offsetY);
                break;
        }
        return true;
    }
}