Android自定义view实现拖动小球移动

/**
 * Created by obo on 15/8/21.
 */
public class TouchView extends View{
 
  public static String TAG = TouchView.class.getCanonicalName();
  //当前小球的位置
  private PointF currrentPosition = new PointF(100,100);
  //手指触摸起点坐标
  private PointF moveStartPosition = new PointF(0,0);
  //当前手指位置坐标
  private PointF moveEndPosition = new PointF(0,0);
 
  private Context context;
 
  public TouchView(Context context, AttributeSet attrs) {
    super(context, attrs);
    this.cOntext= context;
  }
 
  @Override
  public void onDraw(Canvas canvas)
  {
    super.onDraw(canvas);
    canvas.drawCircle(currrentPosition.x + (moveEndPosition.x - moveStartPosition.x),currrentPosition.y+(moveEndPosition.y - moveStartPosition.y),50,new Paint());
  }
 
  @Override
  public boolean onTouchEvent(MotionEvent event) {
 
    switch (event.getActionMasked())
    {
      case MotionEvent.ACTION_DOWN:
        moveStartPosition.x = event.getX();
        moveStartPosition.y = event.getY();
        break;
      case MotionEvent.ACTION_MOVE:
        moveEndPosition.x = event.getX();
        moveEndPosition.y = event.getY();
        //刷新
        this.postInvalidate();
        break;
 
      case MotionEvent.ACTION_UP:
        currrentPosition.x += (moveEndPosition.x - moveStartPosition.x);
        currrentPosition.y += (moveEndPosition.y - moveStartPosition.y);
        moveStartPosition.x = moveEndPosition.x;
        moveStartPosition.y = moveEndPosition.y;
        break;
      default:
    }
    return true;
  }
}

/**
 * Created by obo on 15/8/26.
 */
public class MatrixView extends View {
 
  public final static String TAG = MatrixView.class.getCanonicalName();
  //bitmap运行矩阵
  Matrix matrix = new Matrix();
  //记录点
  PointF startPoint = new PointF();
  //自定义bitmap
  Bitmap bitmap = Bitmap.createBitmap(100,100, Bitmap.Config.ARGB_8888);
 
  public MatrixView(Context context, AttributeSet attrs) {
    super(context, attrs);
 
    Canvas canvas = new Canvas(bitmap);
    //直接在bitmap上面绘制一个小球
    canvas.drawCircle(50,50,50,new Paint());
  }
 
  @Override
  public void onDraw(Canvas canvas)
  {
    super.onDraw(canvas);
 
    canvas.drawBitmap(bitmap, matrix, new Paint());
  }
 
  @Override
  public boolean onTouchEvent(MotionEvent event)
  {
    super.onTouchEvent(event);
 
    if (event.getActionMasked() == MotionEvent.ACTION_MOVE)
    {
      matrix.postTranslate(event.getX() - startPoint.x, event.getY() - startPoint.y );
      //刷新
      this.postInvalidate();
    }
 
    startPoint.x = event.getX();
    startPoint.y = event.getY();
 
    return true;
 
  }
}