android的拖拽有关问题-onTouchEvent事件

android的拖拽问题--onTouchEvent事件

要实现图片的拖拽 主要是通过onTouchEven计算好坐标事件 然后进行重绘。下面的程序是别人的，重新加载 了一次

 img = BitmapFactory.decodeResource(context.getResources(), drawable); 加载一个图片在案例中专门做了一个类 进行设置。

加载图片之后 就可以进行实践判断和重绘

@Override protected void onDraw(Canvas canvas) {
        //canvas.drawColor(0xFFCCCCCC);     //if you want another background color       
        
    	//draw the balls on the canvas
    	for (ColorBall ball : colorballs) {
            canvas.drawBitmap(ball.getBitmap(), ball.getX(), ball.getY(), null);
          }

    }

 

public boolean onTouchEvent(MotionEvent event) {
        int eventaction = event.getAction(); 
        
        int X = (int)event.getX(); 
        int Y = (int)event.getY(); 

        switch (eventaction ) { 

        case MotionEvent.ACTION_DOWN: // touch down so check if the finger is on a ball
        	balID = 0;
        	for (ColorBall ball : colorballs) {
        		// check if inside the bounds of the ball (circle)
        		// get the center for the ball
        		int centerX = ball.getX() + 25;
        		int centerY = ball.getY() + 25;
        		
        		// calculate the radius from the touch to the center of the ball
        		double radCircle  = Math.sqrt( (double) (((centerX-X)*(centerX-X)) + (centerY-Y)*(centerY-Y)));
        		
        		// if the radius is smaller then 23 (radius of a ball is 22), then it must be on the ball
        		if (radCircle < 23){
        			balID = ball.getID();
                    break;
        		}

        		// check all the bounds of the ball (square)
        		//if (X > ball.getX() && X < ball.getX()+50 && Y > ball.getY() && Y < ball.getY()+50){
                //	balID = ball.getID();
                //	break;
                //}
              }
             
             break; 


        case MotionEvent.ACTION_MOVE:   // touch drag with the ball
        	// move the balls the same as the finger
            if (balID > 0) {
            	colorballs[balID-1].setX(X-25);
            	colorballs[balID-1].setY(Y-25);
            }
        	
            break; 

        case MotionEvent.ACTION_UP: 
       		// touch drop - just do things here after dropping

             break; 
        } 
        // redraw the canvas
        invalidate(); 
        return true; 
	
    }