怎么在Android中利用ImageView实现一个放大缩小动画

public class CoolImageView extends ImageView {  private int mLeft = 0;  private int mTop = 0;  private Handler mHandler;  private Bitmap bitmap;  private Rect srcRect = new Rect();  private Rect dstRect = new Rect();  private int imgWidth;  private int imgHeight;  private boolean flag;  private boolean istart;  public CoolImageView(Context context) {    super(context);  }  public CoolImageView(Context context, AttributeSet attrs) {    super(context, attrs);    setUp(context, attrs);  }  public CoolImageView(Context context, AttributeSet attrs, int defStyleAttr) {    super(context, attrs, defStyleAttr);    setUp(context, attrs);  }  private void setUp(Context context, AttributeSet attrs) {    mHandler = new MoveHandler();    mHandler.sendEmptyMessageDelayed(1, 220L);    istart = true;  }  @Override  protected void onDraw(Canvas canvas) {    super.onDraw(canvas);    int width = getWidth();    int height = getHeight();    //获取图片资源    BitmapDrawable drawable = (BitmapDrawable) getDrawable();    bitmap = drawable.getBitmap();    dstRect.left = 0;    dstRect.top = 0;    dstRect.right = width;    dstRect.bottom = height;    if (bitmap != null) {      if (istart) {//        获取图片的宽高        imgWidth = bitmap.getWidth();        imgHeight = bitmap.getHeight();        srcRect.left = 0 + mLeft;        srcRect.right = imgWidth - mLeft;        srcRect.top = 0 + mTop;        srcRect.bottom = imgHeight - mTop;        canvas.drawBitmap(bitmap, srcRect, dstRect, null);      } else {        canvas.drawBitmap(bitmap, null, dstRect, null);      }    }  }  private class MoveHandler extends Handler {    @Override    public void handleMessage(Message msg) {      switch (msg.what) {        case 1:          if (imgHeight != 0) {            if (mTop == 0) {              mTop += 5;              mLeft += 5;            } else if (mTop == 120) {              mTop -= 5;              mLeft -= 5;            }          }          postInvalidate();          mHandler.sendEmptyMessageDelayed(1, 250);          break;      }    }  }  public void start() {    mTop = 0;    mLeft = 0;    istart = true;    mHandler.sendEmptyMessageDelayed(1, 220L);  }  public void stop() {    istart = false;  }}