缩放和在Android中拖动图像

我需要拖动和缩放图像.这是我的代码...

I need to drag and zoom an image. Here is my code ...

//instance variables

Matrix matrix = new Matrix();
Matrix savedMatrix = new Matrix();

static final int NONE = 0;
static final int DRAG = 1;
static final int ZOOM = 2;
int mode = NONE;

PointF start = new PointF();
PointF mid = new PointF();
float oldDist = 1f;

//用于图像查看的OnTouchListener

//OnTouchListener for imageview

OnTouchListener touchAction = new OnTouchListener() {

    @Override
    public boolean onTouch(View v, MotionEvent event) {
        ImageView i = (ImageView)v;

        dragAndZoom(i, event);
        return true; 

    }
};

//执行拖放操作

private void dragAndZoom(View v, MotionEvent event) 
{
    ImageView view = (ImageView) v;
    view.setScaleType(ImageView.ScaleType.MATRIX);
    float scale;

    // Handle touch events here...

    switch (event.getAction() & MotionEvent.ACTION_MASK) 
    {
    case MotionEvent.ACTION_DOWN:  

        // first finger down only
        savedMatrix.set(matrix);
        start.set(event.getX(), event.getY());


         mode = DRAG;
        break;

    case MotionEvent.ACTION_UP: // first finger lifted

    case MotionEvent.ACTION_POINTER_UP: // second finger lifted

        mode = NONE;   

        break;

    case MotionEvent.ACTION_POINTER_DOWN: // first and second finger down

        oldDist = spacing(event);

        if (oldDist > 5f)
        {
            savedMatrix.set(matrix);
            midPoint(mid, event);
            mode = ZOOM;

        }
        break;

    case MotionEvent.ACTION_MOVE:

        if (mode == DRAG) 
        { 
            matrix.set(savedMatrix);

            matrix.postTranslate(event.getX() - start.x, event.getY() - start.y);                

        } 
        else if (mode == ZOOM) 
        { 
            // pinch zooming
            float newDist = spacing(event);

            if (newDist > 5f) 
            {
                matrix.set(savedMatrix);
                scale = newDist / oldDist; 
                matrix.postScale(scale, scale, mid.x, mid.y);
            }
        }
        break;  
    }

    view.setImageMatrix(matrix); // display the transformation on screen


}

  private float spacing(MotionEvent event) 
{
    float x = event.getX(0) - event.getX(1);
    float y = event.getY(0) - event.getY(1);
    return FloatMath.sqrt(x * x + y * y);
}



private void midPoint(PointF point, MotionEvent event) 
{
    float x = event.getX(0) + event.getX(1);
    float y = event.getY(0) + event.getY(1);
    point.set(x / 2, y / 2);
}

行得通.但是有时图像在触摸时会超出屏幕边界.如何始终将图像保留在UI中?请帮我.提前致谢.

It works okay. but sometimes the image is going out of screen boundaries on touch of it. How can i keep the image in UI all the times? Please help me. Thanks in advance.