Android触控事件

触控事件
MotionEvent类：

    /**     * Constant for {@link #getActionMasked}: A pressed gesture has started, the     * motion contains the initial starting location.     *      * This is also a good time to check the button state to distinguish     * secondary and tertiary button clicks and handle them appropriately.     * Use {@link #getButtonState} to retrieve the button state.     * 
     */    //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.     *      * Use {@link #getActionIndex} to retrieve the index of the pointer that changed.     * 
     * The index is encoded in the {@link #ACTION_POINTER_INDEX_MASK} bits of the     * unmasked action returned by {@link #getAction}.     * 
     * 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.     *      * Use {@link #getActionIndex} to retrieve the index of the pointer that changed.     * 
     * The index is encoded in the {@link #ACTION_POINTER_INDEX_MASK} bits of the     * unmasked action returned by {@link #getAction}.     * 
     * 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;    }}

"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" />

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;        }}

"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" />

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;    }}

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