android多点抚摸实例及疑问

多点触摸的一个比较简明的示例：

示例代码出处：http://krvarma-android-samples.googlecode.com/svn/trunk/multitouchsample

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在学习此示例的时候发现multitouch最多可以处理5个手指，5个以上的则不能处理~~

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package com.varma.samples.multitouchsample;import java.util.ArrayList;import android.content.Context;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.DashPathEffect;import android.graphics.Paint;import android.graphics.PointF;import android.util.AttributeSet;//import android.util.FloatMath;import android.view.MotionEvent;import android.view.View;public class MultitouchView extends View {	private static final int STROKE_WIDTH = 1;	private static final int CIRCLE_RADIUS = 20;		private ArrayList<PointF> touchPoints = null;	private Paint drawingPaint = null;	private boolean isMultiTouch = false;	private int pathEffectPhase = 0;	public MultitouchView(Context context) {		super(context);				initialize(context);	}	public MultitouchView(Context context, AttributeSet attrs, int defStyle) {		super(context, attrs, defStyle);				initialize(context);	}	public MultitouchView(Context context, AttributeSet attrs) {		super(context, attrs);				initialize(context);	}		@Override	protected void onDraw(Canvas canvas) {		super.onDraw(canvas);				if(touchPoints.size() > 0)		{			DashPathEffect effect = new DashPathEffect(new float[] {7,7}, pathEffectPhase);			PointF midpt = null;						drawingPaint.setPathEffect(effect);						for(int index=1; index<touchPoints.size(); ++index)			{				midpt = getMidPoint(						touchPoints.get(index - 1).x,touchPoints.get(index - 1).y,						touchPoints.get(index).x,touchPoints.get(index).y);								canvas.drawCircle(						touchPoints.get(index - 1).x,touchPoints.get(index - 1).y, 						1, drawingPaint);				canvas.drawCircle(						touchPoints.get(index - 1).x,touchPoints.get(index - 1).y, 						CIRCLE_RADIUS, drawingPaint);								canvas.drawCircle(touchPoints.get(index).x,touchPoints.get(index).y, 						1, drawingPaint);				canvas.drawCircle(touchPoints.get(index).x,touchPoints.get(index).y, 						CIRCLE_RADIUS, drawingPaint);								canvas.drawLine(						touchPoints.get(index - 1).x,touchPoints.get(index - 1).y,						touchPoints.get(index).x,touchPoints.get(index).y,						drawingPaint);													canvas.drawCircle(midpt.x,midpt.y, 10, drawingPaint);			}						++pathEffectPhase;								invalidate();		}	}		@Override	public boolean onTouchEvent(MotionEvent event) {		super.onTouchEvent(event);				int action = event.getAction() & MotionEvent.ACTION_MASK;				switch(action)		{			case MotionEvent.ACTION_DOWN:			{				invalidate();								break;			}			case MotionEvent.ACTION_POINTER_DOWN:			{				isMultiTouch = true;								setPoints(event);				invalidate();												break;			}			case MotionEvent.ACTION_POINTER_UP:			{				isMultiTouch = false;								break;			}			case MotionEvent.ACTION_MOVE:			{				if(isMultiTouch)				{					setPoints(event);					invalidate();				}								break;			}		}				return true;	}			private void initialize(Context context){		drawingPaint = new Paint();		drawingPaint.setColor(Color.RED);		drawingPaint.setStrokeWidth(STROKE_WIDTH);		drawingPaint.setStyle(Paint.Style.STROKE);		drawingPaint.setAntiAlias(true);				touchPoints = new ArrayList<PointF>();	}		public void setPoints(MotionEvent event){		touchPoints.clear();				int pointerIndex = 0;				for(int index=0; index<event.getPointerCount(); ++index)		{			pointerIndex = event.getPointerId(index);						touchPoints.add(new PointF(event.getX(pointerIndex),event.getY(pointerIndex)));		}	}	private PointF getMidPoint(float x1,float y1, float x2, float y2) {		PointF point = new PointF();				float x = x1 + x2;		float y = y1 + y2;				point.set(x / 2, y / 2);				return point;	}}

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示例图：