近期须要实现一个功能，在Activity中有一个手写区域，为了更好的用户体验，须要满足即使整个手掌放在屏幕上时（android平板，屏幕比較大）也仅仅响应手写区域内的操作，即在支持多点触控的情况下，仅仅响应指定的区域，我将这个功能称作“手掌抑制”，即在手写时。手掌放在屏幕上面不做不论什么响应。

初看这个功能非常easy，依照之前处理listview、gridview里面的子view不能响应的方式，仅仅要在activity层不拦截向手写view传递的消息就可以实现想要的效果，但经过实际測试和对android消息机制的具体研究发现。要实现这个功能会有点小复杂。

一、android的消息传递机制：

1、基础知识：

(1) 全部Touch事件都被封装成了MotionEvent对象。包含Touch的位置、时间、历史记录以及第几个手指(多指触摸)等。

(2) 事件类型分为ACTION_DOWN, ACTION_UP, ACTION_MOVE, ACTION_POINTER_DOWN, ACTION_POINTER_UP, ACTION_CANCEL，每一个事件都是以ACTION_DOWN開始ACTION_UP结束。

(3) 对事件的处理包含三类：

传递——dispatchTouchEvent()

拦截——onInterceptTouchEvent()

消费——onTouchEvent()和OnTouchListener

2、传递流程

(1) 事件从Activity.dispatchTouchEvent()開始传递，仅仅要没有被停止或拦截，从最上层的View(ViewGroup)開始一直往下(子View)传递。子View能够通过onTouchEvent()对事件进行处理。

(2) 事件由父View(ViewGroup)传递给子View，ViewGroup能够通过onInterceptTouchEvent()对事件做拦截，停止其往下传递。

(3) 假设事件从上往下传递过程中一直没有被停止，且最底层子View没有消费事件。事件会反向往上传递，这时父View(ViewGroup)能够进行消费，假设还是没有被消费的话，最后会到Activity的onTouchEvent()函数。

(4) 假设View没有对ACTION_DOWN进行消费，之后的其它事件不会传递过来。

(5) OnTouchListener优先于onTouchEvent()对事件进行消费。

上面的消费即表示对应函数返回值为true。

3、实际情况：

可以响应事件处理方法的控件包含：ViewGroup、View、Activity，各类控件对三个事件响应处理方法的支持情况例如以下：

这三个控件。Activity是处于最外层的，消息的传递首先是系统回调消息给Activity。Activity将消息传递给每个ViewGroup，然后ViewGroup会将消息传递给对应地子View。

本文所描写叙述的手写控件是一个view，在有系统消息回调时仅仅有上层控件将消息分发下来，它才可以消费和处理这些消息。

二、问题现象：

接着我们进入正题，依照我在开篇介绍的那种处理方式，写一个手写view，在Activity和ViewGroup（自己定义一个Layout就可以）层将消息分发给该view，眼下的代码看上去是这样子的：

public class DrawView extends View {
public DrawView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
initPaintView( );
}

public DrawView(Context context, AttributeSet attrs) {  
    super(context, attrs);  
    initPaintView( );  
}

public DrawView(Context context) {  
    super(context);  
    initPaintView( );  
}

public void clear() {  
    if (null != mPath) {  
        mPath.reset();  
        invalidate();  
    }  
}  

private void initPaintView() {  
    mPaint.setAntiAlias(true);  
    mPaint.setColor(Color.WHITE);  
    mPaint.setStyle(Paint.Style.STROKE);  
    mPaint.setStrokeJoin(Paint.Join.ROUND);  
    mPaint.setStrokeWidth(5f);  
}

@Override  
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {  
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);  
    mViewWidth = MeasureSpec.getSize(widthMeasureSpec);   //获取ViewGroup宽度  
    mViewHeight = MeasureSpec.getSize(heightMeasureSpec);  //获取ViewGroup高度  
}

@Override  
protected void onDraw(Canvas canvas) {  
    canvas.drawPath(mPath, mPaint);  
}  

public boolean inArea( float x, float y ){  
    return ( x >= 0 && x <= mViewWidth && y >= 0 && y <= mViewHeight)?true:false;  
}

@Override  
public boolean onTouchEvent(MotionEvent event) {  
    float eventX = event.getX( );  
    float eventY = event.getY( );

    switch (event.getAction()) {  
    case MotionEvent.ACTION\_DOWN: {  
        mPath.moveTo(eventX, eventY);  
        mLastTouchX = eventX;  
        mLastTouchY = eventY;  
        invalidate( );  
    }  
        return true;  
    case MotionEvent.ACTION\_MOVE:{  
        drawView( event, eventX, eventY );  
    }  
    break;  
    case MotionEvent.ACTION\_UP:{  
        drawView( event, eventX, eventY );  
    }  
        break;  
    default:  
        return false;  
    }  

    return true;  
}

private void drawView( MotionEvent event, float eventX, float eventY ){  
    resetDirtyRect(eventX, eventY);  
    int historySize = event.getHistorySize();  
    for (int i = 0; i < historySize; i++) {  
        float historicalX = event.getHistoricalX(i);  
        float historicalY = event.getHistoricalY(i);  
        getDirtyRect(historicalX, historicalY);  
        mPath.lineTo(historicalX, historicalY);  
    }  

    mPath.lineTo(eventX, eventY);  
    invalidate((int) (mDirtyRect.left - HALF\_STROKE\_WIDTH),  
            (int) (mDirtyRect.top - HALF\_STROKE\_WIDTH),  
            (int) (mDirtyRect.right + HALF\_STROKE\_WIDTH),  
            (int) (mDirtyRect.bottom + HALF\_STROKE\_WIDTH));

    mLastTouchX = eventX;  
    mLastTouchY = eventY;  
}

private void getDirtyRect(float historicalX, float historicalY) {  
    if (historicalX < mDirtyRect.left) {  
        mDirtyRect.left = historicalX;  
    } else if (historicalX > mDirtyRect.right) {  
        mDirtyRect.right = historicalX;  
    }  
    if (historicalY < mDirtyRect.top) {  
        mDirtyRect.top = historicalY;  
    } else if (historicalY > mDirtyRect.bottom) {  
        mDirtyRect.bottom = historicalY;  
    }  
}  

private void resetDirtyRect(float eventX, float eventY) {  
    mDirtyRect.left = Math.min(mLastTouchX, eventX);  
    mDirtyRect.right = Math.max(mLastTouchX, eventX);  
    mDirtyRect.top = Math.min(mLastTouchY, eventY);  
    mDirtyRect.bottom = Math.max(mLastTouchY, eventY);  
}  

private static final float STROKE\_WIDTH = 5f;  
private static final float HALF\_STROKE\_WIDTH = STROKE\_WIDTH / 2;  
private float mLastTouchX = 0;  
private float mLastTouchY = 0;

private int mViewWidth = 0;  
private int mViewHeight = 0;

private final RectF mDirtyRect = new RectF();  
private Paint mPaint = new Paint();  
private Path mPath = new Path();  

}

你会发现，当你将activity的dispatchTouchEvent和viewgroup的dispatchTouchEvent、onInterceptTouchEvent方法的返回值都设置为false时，整个屏幕都不会响应不论什么消息了，当我们去掉activity和viewgroup的dispatchTouchEvent方法，仅仅有viewgroup的onInterceptTouchEvent返回值被置为false时，手写区域可以响应。但当手掌靠在手写区域外，在手写区域内手写就失效了，事实上和去掉viewgroupd的onInterceptTouchEvent方法效果是一样的，也就是说明这样的处理方式是不可行的。

三、解决方式：

加了同意分发消息的方法。不拦截向下分发消息反而还不行，这个问题详细原因我没有找到。个人觉得是系统针对activity的消息事件处理做了特殊处理，它的优先级是最高的，尽管能够复写它的消息分发dispatchTouchEvent方法，可是无论是返回true还是false结果都是屏幕不能响应不论什么操作。这一点有知道的大拿欢迎指点指点。

要实现本文想要的功能显然不能使用开篇讲到的方法，在研究这个问题的过程中，发现尽管activity的dispatchTouchEvent无法控制，但其onTouchEvent方法是有效的，仅仅要在屏幕的不论什么一个地方操作，onTouchEvent里面都会有打印消息，细致回想上面提到的android消息分发机制会发现，仅仅要我们在屏幕上操作时，模拟系统在activity的onTouchEvent方法里面向手写view派发消息就可以实现想要的功能。详细方法例如以下：

1、向下派发消息的实现以及view和activity之间的坐标转换：

如上面所讲，当在屏幕上操作时监听activity的onTouchEvent方法，将在手写控件内的操作派发给手写view就可以实现想要的功能。

（1）坐标转换：

本文的手写view基于activity居中的，它的坐标原点和activity的坐标原点不同样，为了推断在acitivity上操作的地方是否在手写view内。须要通过坐标转换之后才干推断：

如上图所看到的，在activity中推断一个点(x,y)是否在手写view里面时，转换成的坐标应该是(x-view.getLeft(),y-view.getTop())。

（2）眼下的view和activity看起来是这样子的：

DrawView：

public class DrawView extends View {
public DrawView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
initPaintView( );
}

public DrawView(Context context, AttributeSet attrs) {  
    super(context, attrs);  
    initPaintView( );  
}

public DrawView(Context context) {  
    super(context);  
    initPaintView( );  
}

public void clear() {  
    if (null != mPath) {  
        mPath.reset();  
        invalidate();  
    }  
}  

private void initPaintView() {  
    mPaint.setAntiAlias(true);  
    mPaint.setColor(Color.WHITE);  
    mPaint.setStyle(Paint.Style.STROKE);  
    mPaint.setStrokeJoin(Paint.Join.ROUND);  
    mPaint.setStrokeWidth(5f);  
}

@Override  
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {  
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);  
    mViewWidth = MeasureSpec.getSize(widthMeasureSpec);   //获取ViewGroup宽度  
    mViewHeight = MeasureSpec.getSize(heightMeasureSpec);  //获取ViewGroup高度  
}

@Override  
protected void onDraw(Canvas canvas) {  
    canvas.drawPath(mPath, mPaint);  
}  

public boolean inArea( float x, float y ){  
    return ( x >= 0 && x <= mViewWidth && y >= 0 && y <= mViewHeight)?true:false;  
}

@Override  
public boolean onTouchEvent(MotionEvent event) {  
    float eventX = -1;  
    float eventY = -1;  
    int pointId = 0;  
    int pointCnt = event.getPointerCount( );  
    for( int index = 0; index < pointCnt; index++ ){  
        if( inArea( event.getX( index ) - getLeft( ), event.getY( index ) - getTop( ) ) ){  
            pointId = index;  
            eventX = event.getX( index ) - getLeft( );  
            eventY = event.getY( index ) - getTop( );  
            break;  
        }  
    }

    if( ( eventX == -1 || eventY == -1 ) || ( eventX == 0 || eventY == 0 ) ){  
        return false;  
    }

    switch (event.getAction()) {  
    case MotionEvent.ACTION\_DOWN: {  
        mPath.moveTo(eventX, eventY);  
        mLastTouchX = eventX;  
        mLastTouchY = eventY;  
        invalidate( );  
    }  
        return true;  
    case MotionEvent.ACTION\_MOVE:{  
        drawView( event, eventX, eventY, pointId );  
    }  
    break;  
    case MotionEvent.ACTION\_UP:{  
        drawView( event, eventX, eventY, pointId );  
    }  
        break;  
    default:  
        return false;  
    }  

    return true;  
}

private void drawView( MotionEvent event, float eventX, float eventY, int pointId ){  
    resetDirtyRect(eventX, eventY);  
    int historySize = event.getHistorySize();  
    for (int i = 0; i < historySize; i++) {  
        float historicalX = event.getHistoricalX(pointId,i) - getLeft( );  
        float historicalY = event.getHistoricalY(pointId,i) - getTop( );  
        getDirtyRect(historicalX, historicalY);  
        mPath.lineTo(historicalX, historicalY);  
    }  

    mPath.lineTo(eventX, eventY);  
    invalidate((int) (mDirtyRect.left - HALF\_STROKE\_WIDTH),  
            (int) (mDirtyRect.top - HALF\_STROKE\_WIDTH),  
            (int) (mDirtyRect.right + HALF\_STROKE\_WIDTH),  
            (int) (mDirtyRect.bottom + HALF\_STROKE\_WIDTH));

    mLastTouchX = eventX;  
    mLastTouchY = eventY;  
}

private void getDirtyRect(float historicalX, float historicalY) {  
    if (historicalX < mDirtyRect.left) {  
        mDirtyRect.left = historicalX;  
    } else if (historicalX > mDirtyRect.right) {  
        mDirtyRect.right = historicalX;  
    }  
    if (historicalY < mDirtyRect.top) {  
        mDirtyRect.top = historicalY;  
    } else if (historicalY > mDirtyRect.bottom) {  
        mDirtyRect.bottom = historicalY;  
    }  
}  

private void resetDirtyRect(float eventX, float eventY) {  
    mDirtyRect.left = Math.min(mLastTouchX, eventX);  
    mDirtyRect.right = Math.max(mLastTouchX, eventX);  
    mDirtyRect.top = Math.min(mLastTouchY, eventY);  
    mDirtyRect.bottom = Math.max(mLastTouchY, eventY);  
}  

private static final float STROKE\_WIDTH = 5f;  
private static final float HALF\_STROKE\_WIDTH = STROKE\_WIDTH / 2;  
private float mLastTouchX = 0;  
private float mLastTouchY = 0;

private int mViewWidth = 0;  
private int mViewHeight = 0;

private final RectF mDirtyRect = new RectF();  
private Paint mPaint = new Paint();  
private Path mPath = new Path();  

}

Activity：

@Override
public boolean onTouchEvent(MotionEvent event) {
int pointCnt = event.getPointerCount( );
for( int index = 0; index < pointCnt; index++ ){
if( mDrawView.inArea( event.getX( index ) - mDrawView.getLeft( ), event.getY( index ) - mDrawView.getTop( ) ) ){
mDrawView.onTouchEvent( event );
System.out.println( "action === pointIndex " + index );
return false;
}
}

    //mDrawView.setInView( false );  
    return super.onTouchEvent(event);  
}

DrawView的inArea方法为核心方法。经过上面的处理后，可以实现当手掌放在手写区域外时在手写区域手写的功能。效果例如以下图所看到的。但你会发现当在手写区域手写的手指抬起再放下继续手写时，会直接画一条直线。通过接下来对android事件机制中ACTION_DOWN和ACTION_UP消息的分析，该问题将会得到解决。

2、android消息事件中ACTION_DOWN和ACTION_UP的触发时机即改善方案：

通过实际測试发现，android消息事件中ACTION_DOWN和ACTION_UP的触发时机分别为：

ACTION_DOWN：仅仅要有手指接触屏幕即会触发；

ACTION_UP：当屏幕上没有不论什么触控操作时触发；

对于多点触控。当某个手指抬起或者松开时会分别触发：ACTION_POINTER_DOWN和ACTION_POINTER_UP，所以对于上面遇到的问题，是因为在多点触控的情况下，仅仅点下或者松开某一根手指时，这两个消息不会触发导致，将ACTION_POINTER_DOWN和ACTION_POINTER_UP这两类消息在DrawView的onTouchEvent方法中一并处理就可以解决，改善后的view代码是这样子的：

public class DrawView extends View {
public DrawView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
initPaintView( );
}

public DrawView(Context context, AttributeSet attrs) {  
    super(context, attrs);  
    initPaintView( );  
}

public DrawView(Context context) {  
    super(context);  
    initPaintView( );  
}

public void clear() {  
    if (null != mPath) {  
        mPath.reset();  
        invalidate();  
    }  
}  

private void initPaintView() {  
    mPaint.setAntiAlias(true);  
    mPaint.setColor(Color.WHITE);  
    mPaint.setStyle(Paint.Style.STROKE);  
    mPaint.setStrokeJoin(Paint.Join.ROUND);  
    mPaint.setStrokeWidth(5f);  
}

@Override  
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {  
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);  
    mViewWidth = MeasureSpec.getSize(widthMeasureSpec);   //获取ViewGroup宽度  
    mViewHeight = MeasureSpec.getSize(heightMeasureSpec);  //获取ViewGroup高度  
}

@Override  
protected void onDraw(Canvas canvas) {  
    canvas.drawPath(mPath, mPaint);  
}  

public boolean inArea( float x, float y ){  
    return ( x >= 0 && x <= mViewWidth && y >= 0 && y <= mViewHeight)?

true:false;
}

@Override  
public boolean onTouchEvent(MotionEvent event) {  
    float eventX = -1;  
    float eventY = -1;  
    int pointId = 0;  
    int pointCnt = event.getPointerCount( );  
    for( int index = 0; index < pointCnt; index++ ){  
        if( inArea( event.getX( index ) - getLeft( ), event.getY( index ) - getTop( ) ) ){  
            pointId = index;  
            eventX = event.getX( index ) - getLeft( );  
            eventY = event.getY( index ) - getTop( );  
            break;  
        }  
    }

    if( ( eventX == -1 || eventY == -1 ) || ( eventX == 0 || eventY == 0 ) ){  
        return false;  
    }

    switch (event.getAction()) {  
    case MotionEvent.ACTION\_POINTER\_1\_DOWN:  
    case MotionEvent.ACTION\_POINTER\_2\_DOWN:  
    case MotionEvent.ACTION\_POINTER\_3\_DOWN:  
    case MotionEvent.ACTION\_DOWN: {  
        mPath.moveTo(eventX, eventY);  
        mLastTouchX = eventX;  
        mLastTouchY = eventY;  
        invalidate( );  
    }  
        return true;  
    case MotionEvent.ACTION\_MOVE:{  
        drawView( event, eventX, eventY, pointId );  
    }  
    break;  
    case MotionEvent.ACTION\_UP:  
    case MotionEvent.ACTION\_POINTER\_1\_UP:  
    case MotionEvent.ACTION\_POINTER\_2\_UP:  
    case MotionEvent.ACTION\_POINTER\_3\_UP:{  
        drawView( event, eventX, eventY, pointId );  
    }  
        break;  
    default:  
        return false;  
    }  

    return true;  
}

private void drawView( MotionEvent event, float eventX, float eventY, int pointId ){  
    resetDirtyRect(eventX, eventY);  
    int historySize = event.getHistorySize();  
    for (int i = 0; i < historySize; i++) {  
        float historicalX = event.getHistoricalX(pointId,i) - getLeft( );  
        float historicalY = event.getHistoricalY(pointId,i) - getTop( );  
        getDirtyRect(historicalX, historicalY);  
        mPath.lineTo(historicalX, historicalY);  
    }  

    mPath.lineTo(eventX, eventY);  
    invalidate((int) (mDirtyRect.left - HALF\_STROKE\_WIDTH),  
            (int) (mDirtyRect.top - HALF\_STROKE\_WIDTH),  
            (int) (mDirtyRect.right + HALF\_STROKE\_WIDTH),  
            (int) (mDirtyRect.bottom + HALF\_STROKE\_WIDTH));

    mLastTouchX = eventX;  
    mLastTouchY = eventY;  
}

private void getDirtyRect(float historicalX, float historicalY) {  
    if (historicalX < mDirtyRect.left) {  
        mDirtyRect.left = historicalX;  
    } else if (historicalX > mDirtyRect.right) {  
        mDirtyRect.right = historicalX;  
    }  
    if (historicalY < mDirtyRect.top) {  
        mDirtyRect.top = historicalY;  
    } else if (historicalY > mDirtyRect.bottom) {  
        mDirtyRect.bottom = historicalY;  
    }  
}  

private void resetDirtyRect(float eventX, float eventY) {  
    mDirtyRect.left = Math.min(mLastTouchX, eventX);  
    mDirtyRect.right = Math.max(mLastTouchX, eventX);  
    mDirtyRect.top = Math.min(mLastTouchY, eventY);  
    mDirtyRect.bottom = Math.max(mLastTouchY, eventY);  
}  

private static final float STROKE\_WIDTH = 5f;  
private static final float HALF\_STROKE\_WIDTH = STROKE\_WIDTH / 2;  
private float mLastTouchX = 0;  
private float mLastTouchY = 0;

private int mViewWidth = 0;  
private int mViewHeight = 0;

private final RectF mDirtyRect = new RectF();  
private Paint mPaint = new Paint();  
private Path mPath = new Path();  

}

效果也算比較理想了：

3、边界问题处理：

经过上面两步操作，基本上可以实现手掌抑制功能了，但经过细致測试会发现，当多点触控屏幕时。某根手指从手写控件外移动到手写控件内时，会在手写区域边界直接绘制成直线的现象，例如以下图：

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这是由于在android中一个完整的消息流程离不开ACTION_DOWN和ACTION_UP，当手指从手写区域外移动到手写区域内时，手写区域根本没有接收到ACTION_DOWN消息，针对这样的情况，我们须要在activity中对view做特殊处理。即当检測到有手指在手写区域但没有触发ACTION_DOWN消息时，在ACTION_MOVE消息中处理ACTION_DOWN消息应该处理的事情。

改善后的代码是这个样子的：

DrawView：

public class DrawView extends View {
public DrawView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
initPaintView( );
}

public DrawView(Context context, AttributeSet attrs) {  
    super(context, attrs);  
    initPaintView( );  
}

public DrawView(Context context) {  
    super(context);  
    initPaintView( );  
}

public void clear() {  
    if (null != mPath) {  
        mPath.reset();  
        invalidate();  
    }  
}  

private void initPaintView() {  
    mPaint.setAntiAlias(true);  
    mPaint.setColor(Color.WHITE);  
    mPaint.setStyle(Paint.Style.STROKE);  
    mPaint.setStrokeJoin(Paint.Join.ROUND);  
    mPaint.setStrokeWidth(5f);  
}

@Override  
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {  
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);  
    mViewWidth = MeasureSpec.getSize(widthMeasureSpec);   //获取ViewGroup宽度  
    mViewHeight = MeasureSpec.getSize(heightMeasureSpec);  //获取ViewGroup高度  
}

@Override  
protected void onDraw(Canvas canvas) {  
    canvas.drawPath(mPath, mPaint);  
}  

public boolean inArea( float x, float y ){  
    return ( x >= 0 && x <= mViewWidth && y >= 0 && y <= mViewHeight)?

true:false;
}

@SuppressWarnings("deprecation")  
@Override  
public boolean onTouchEvent(MotionEvent event) {  
    float eventX = -1;  
    float eventY = -1;  
    int pointId = 0;  
    int pointCnt = event.getPointerCount( );  
    for( int index = 0; index < pointCnt; index++ ){  
        if( inArea( event.getX( index ) - getLeft( ), event.getY( index ) - getTop( ) ) ){  
            pointId = index;  
            eventX = event.getX( index ) - getLeft( );  
            eventY = event.getY( index ) - getTop( );  
            break;  
        }  
    }

    if( ( eventX == -1 || eventY == -1 ) || ( eventX == 0 || eventY == 0 ) ){  
        return false;  
    }

    switch (event.getAction()) {  
    case MotionEvent.ACTION\_POINTER\_1\_DOWN:  
    case MotionEvent.ACTION\_POINTER\_2\_DOWN:  
    case MotionEvent.ACTION\_POINTER\_3\_DOWN:  
    case MotionEvent.ACTION\_DOWN: {  
        mPath.moveTo(eventX, eventY);  
        mLastTouchX = eventX;  
        mLastTouchY = eventY;  
        mInView = true;  
        invalidate( );  
    }  
        return true;  
    case MotionEvent.ACTION\_MOVE:{  
        if( !mInView ){  
            mInView = true;  
            mLastTouchX = eventX;  
            mLastTouchY = eventY;  
            mPath.moveTo(eventX, eventY);  
        }  
        drawView( event, eventX, eventY, pointId );  
    }  
    break;  
    case MotionEvent.ACTION\_UP:  
    case MotionEvent.ACTION\_POINTER\_1\_UP:  
    case MotionEvent.ACTION\_POINTER\_2\_UP:  
    case MotionEvent.ACTION\_POINTER\_3\_UP:{  
        drawView( event, eventX, eventY, pointId );  
    }  
        break;  
    default:  
        return false;  
    }  

    return true;  
}

public void setInView( boolean inView ){  
    mInView = inView;  
}

private void drawView( MotionEvent event, float eventX, float eventY, int pointId ){  
    resetDirtyRect(eventX, eventY);  
    int historySize = event.getHistorySize();  
    for (int i = 0; i < historySize; i++) {  
        float historicalX = event.getHistoricalX(pointId,i) - getLeft( );  
        float historicalY = event.getHistoricalY(pointId,i) - getTop( );  
        getDirtyRect(historicalX, historicalY);  
        mPath.lineTo(historicalX, historicalY);  
    }  

    mPath.lineTo(eventX, eventY);  
    invalidate((int) (mDirtyRect.left - HALF\_STROKE\_WIDTH),  
            (int) (mDirtyRect.top - HALF\_STROKE\_WIDTH),  
            (int) (mDirtyRect.right + HALF\_STROKE\_WIDTH),  
            (int) (mDirtyRect.bottom + HALF\_STROKE\_WIDTH));

    mLastTouchX = eventX;  
    mLastTouchY = eventY;  
}

private void getDirtyRect(float historicalX, float historicalY) {  
    if (historicalX < mDirtyRect.left) {  
        mDirtyRect.left = historicalX;  
    } else if (historicalX > mDirtyRect.right) {  
        mDirtyRect.right = historicalX;  
    }  
    if (historicalY < mDirtyRect.top) {  
        mDirtyRect.top = historicalY;  
    } else if (historicalY > mDirtyRect.bottom) {  
        mDirtyRect.bottom = historicalY;  
    }  
}  

private void resetDirtyRect(float eventX, float eventY) {  
    mDirtyRect.left = Math.min(mLastTouchX, eventX);  
    mDirtyRect.right = Math.max(mLastTouchX, eventX);  
    mDirtyRect.top = Math.min(mLastTouchY, eventY);  
    mDirtyRect.bottom = Math.max(mLastTouchY, eventY);  
}  

private static final float STROKE\_WIDTH = 5f;  
private static final float HALF\_STROKE\_WIDTH = STROKE\_WIDTH / 2;  
private float mLastTouchX = 0;  
private float mLastTouchY = 0;

private boolean mInView = false;  
private int mViewWidth = 0;  
private int mViewHeight = 0;

private final RectF mDirtyRect = new RectF();  
private Paint mPaint = new Paint();  
private Path mPath = new Path();  

}

activity也须要添加一句话：

@Override
public boolean onTouchEvent(MotionEvent event) {
int pointCnt = event.getPointerCount( );
for( int index = 0; index < pointCnt; index++ ){
if( mDrawView.inArea( event.getX( index ) - mDrawView.getLeft( ), event.getY( index ) - mDrawView.getTop( ) ) ){
mDrawView.onTouchEvent( event );
System.out.println( "action === pointIndex " + index );
return false;
}
}

    mDrawView.setInView( false );  
    return super.onTouchEvent(event);  
}

最后最终实现了我们想要的效果：

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四、參考文档：

Android Touch事件传递机制

Android 编程下 Touch 事件的分发和消费机制

五、代码：

最后附上本文的代码：Android手掌抑制demo