简单的多点触摸放缩图片

public class MultiTouch extends Activity{

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		// TODO Auto-generated method stub
		super.onCreate(savedInstanceState);
		this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
		requestWindowFeature(Window.FEATURE_NO_TITLE);
		setContentView(new MultiTouchView(this));
	}
}

class MultiTouchView extends SurfaceView implements Callback,Runnable{
	private SurfaceHolder mSurfaceHolder;
	private Thread mThread;
	private Canvas mCanvas;
	private Paint mPaint;
	private boolean mFlag;
	private float mOldScaleRate=1;
	private float mScaleRate=1;
	private float mNewDistance;
	private float mOldDistance;
	private Bitmap mBitmap;
	private int mScreenW;
	private int mScreenH;

	public MultiTouchView(Context context) {
		super(context);
		mSurfaceHolder=this.getHolder();
		mSurfaceHolder.addCallback(this);
		mPaint=new Paint();
		mPaint.setColor(Color.WHITE);
		mPaint.setAntiAlias(true);
		mBitmap=BitmapFactory.decodeResource(getResources(), R.drawable.icon);
		setFocusable(true);
		setFocusableInTouchMode(true);
	}

	@Override
	public void surfaceChanged(SurfaceHolder holder, int format, int width,
			int height) {
		// TODO Auto-generated method stub
		
	}

	@Override
	public void surfaceCreated(SurfaceHolder holder) {
		mScreenW=this.getWidth();
		mScreenH=this.getHeight();
		mFlag=true;
		mThread=new Thread(this,"My Thread");
		mThread.start();
	}

	@Override
	public void surfaceDestroyed(SurfaceHolder holder) {
		mFlag=false;
	}

	@Override
	public void run() {
		while (mFlag) {
			long start=System.currentTimeMillis();
			myDraw();
			logic();
			long end=System.currentTimeMillis();
			if ((end-start)<50) {
				try {
					Thread.sleep(50-(end-start));
				} catch (InterruptedException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
			}
		}
	}

	private void logic() {
		// TODO Auto-generated method stub
		
	}

	private void myDraw() {
		try {
			mCanvas=mSurfaceHolder.lockCanvas();
			if (mCanvas != null) {
				mCanvas.drawColor(Color.WHITE);
				mCanvas.save();
				mCanvas.scale(mScaleRate, mScaleRate, mScreenW/2, mScreenH/2);
				mCanvas.drawBitmap(mBitmap, mScreenW/2-mBitmap.getWidth()/2, mScreenH/2-mBitmap.getHeight()/2, mPaint);
				mCanvas.restore();
			}
		} catch (Exception e) {
			// TODO: handle exception
		}finally{
			if(mCanvas != null){
				mSurfaceHolder.unlockCanvasAndPost(mCanvas);
			}
		}
	}
	
	@Override
	public boolean onTouchEvent(MotionEvent event) {
		requestFocus();
		switch (event.getAction() & MotionEvent.ACTION_MASK) {
		case MotionEvent.ACTION_POINTER_UP:
			mOldScaleRate=mScaleRate;
			break;
		case MotionEvent.ACTION_POINTER_DOWN:
			mOldDistance = getEventSpace(event);
			break;
		case MotionEvent.ACTION_MOVE:
			if (event.getPointerCount()==2) {
				mNewDistance = getEventSpace(event);
				if (mOldDistance != 0) {
					mScaleRate = mOldScaleRate * mNewDistance / mOldDistance;
				}
			}
			return true;
		default:
			break;
		}
		return true;
		//return super.onTouchEvent(event);
	}

	private float getEventSpace(MotionEvent event) {
		float disX=event.getX(1)-event.getX(0);
		float disY=event.getY(1)-event.getY(0);
		return FloatMath.sqrt(disX*disX+disY*disY);
	}
}

问题一：

当手指进行多点触摸的时候，无法进入相应的case语句进行执行，刚开始以为是没有加setFocusableInTouchMode(true);，但是发现即使加了这句话还是不能正常的执行，经过几次尝试发现是因为

@Override
	public boolean onTouchEvent(MotionEvent event) {
		requestFocus();
		switch (event.getAction() & MotionEvent.ACTION_MASK) {
		case MotionEvent.ACTION_POINTER_UP:
			mOldScaleRate=mScaleRate;
			break;
		case MotionEvent.ACTION_POINTER_DOWN:
			mOldDistance = getEventSpace(event);
			break;
		case MotionEvent.ACTION_MOVE:
			if (event.getPointerCount()==2) {
				mNewDistance = getEventSpace(event);
				if (mOldDistance != 0) {
					mScaleRate = mOldScaleRate * mNewDistance / mOldDistance;
				}
			}
			return true;
		default:
			break;
		}
		return true;
		//return super.onTouchEvent(event);
	}

应该返回return true;而不是return super.onTouchEvent(event);API解释：

Returns:

True if the event was handled, false otherwise.

问题二：

case MotionEvent.ACTION_MOVE:
        mNewDistance = getEventSpace(event);
	if (mOldDistance != 0) {
		mScaleRate = mNewDistance / mOldDistance;
	}
        return true;

之前是按照上面的方法做的，发现图片是可以进行放缩，但是放所的不正常

case MotionEvent.ACTION_MOVE:
			if (event.getPointerCount()==2) {
				mNewDistance = getEventSpace(event);
				if (mOldDistance != 0) {
					mScaleRate = mOldScaleRate * mNewDistance / mOldDistance;
				}
			}
			return true;

改成上面的做法后正常了，我每次在抬起手指也就是触发MotionEvent.ACTION_POINTER_UP的时候应该将上一次的放缩比例保存起来，下一次计算放缩比例的时候应该在这个的基础上进行放缩。