Android GridView 拖動item

public class DragGridView extends GridView
{
    private String TAG = "DragGridView";
   
    private int dragPosition; //開始拖拽的位置
   
    private int dropPosition; //結束拖拽的位置
   
    private int dragPointX; //相對於item的X座標
   
    private int dragPointY; //相對於item的y座標
   
    private int dragOffsetX;
   
    private int dragOffsetY;
   
    private ImageView dragImageView; //拖動item的preview
   
    private WindowManager windowManager;
   
    private WindowManager.LayoutParams windowParams;
   
    public DragGridView(Context context)
    {
        super(context);
    }
   
    public DragGridView(Context context, AttributeSet attrs)
    {
        super(context, attrs);
    }
   
    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev)
    {
        Log.d(TAG, "onInterceptTouchEvent" + super.onInterceptTouchEvent(ev));
        if (ev.getAction() == MotionEvent.ACTION_DOWN)
        {
            int x = (int)ev.getX();
            int y = (int)ev.getY();
            Log.d(TAG, "x=" + x + "getRawx=" + ev.getRawX());
            Log.d(TAG, "y=" + y + "getRawY=" + ev.getRawY());
            dragPosition = dropPosition = pointToPosition(x, y);
            Log.i("TAG", "dragPosition=" + dragPosition);
            if (dragPosition == AdapterView.INVALID_POSITION)
            {
                return super.onInterceptTouchEvent(ev);
            }
            Log.d(TAG, "getFirstPosition" + getFirstVisiblePosition());
            View itemView = (View)getChildAt(dragPosition - getFirstVisiblePosition());
            //得到當前點在item內部的位移量即相對於item左上方的座標
            Log.d(TAG, "itemview.getLeft=" + itemView.getLeft() + ",itemview.getTop=" + itemView.getTop());
           
            dragPointX = x - itemView.getLeft();//得到觸摸的點,在item 內部相對於它的左邊的點的座標
            dragPointY = y - itemView.getTop();
           
            //item 左上方的座標.(x,y)
            dragOffsetX = (int)(ev.getRawX() - x);
            dragOffsetY = (int)(ev.getRawY() - y);
           
            Log.d(TAG, "dragPointX=" + dragPointX + ",dragPointY=" + dragPointY + ",dragOffsetX=" + dragOffsetX
                + ",dragOffsetY=" + dragOffsetY);
           
            //解決問題3
            //每次都銷毀一次cache,重建一個bitmap
            itemView.destroyDrawingCache();
            itemView.setDrawingCacheEnabled(true);
            Bitmap bm = Bitmap.createBitmap(itemView.getDrawingCache());
           
            //建立item的縮圖
            startDrag(bm, x, y);
            return false;
        }
        return super.onInterceptTouchEvent(ev);
    }
   
    private void startDrag(Bitmap bm, int x, int y)
    {
        stopDrag();
        windowParams = new WindowManager.LayoutParams();
        Log.i("xqqLog", "X:" + x + " dragPointX:" + dragPointX + " dragOffsetX:" + dragOffsetX);
        windowParams.gravity = Gravity.TOP | Gravity.LEFT; //這個必須加
        //得到preview左上方相對於螢幕的座標
        windowParams.x = x - dragPointX + dragOffsetX;
        windowParams.y = y - dragPointY + dragOffsetY;
        //設定寬和高
        windowParams.height = WindowManager.LayoutParams.WRAP_CONTENT;
        windowParams.width = WindowManager.LayoutParams.WRAP_CONTENT;
        windowParams.flags =
            WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE | WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE
                | WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON | WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN;
       
        windowParams.format = PixelFormat.TRANSLUCENT;
        windowParams.windowAnimations = 0;
       
        ImageView iv = new ImageView(getContext());
        iv.setImageBitmap(bm);
        windowManager = (WindowManager)getContext().getSystemService(Context.WINDOW_SERVICE);//"window"

        windowManager.addView(iv, windowParams);
        dragImageView = iv;
       
    }
   
    @Override
    public boolean onTouchEvent(MotionEvent ev)
    {
        if (dragImageView != null && dragPosition != AdapterView.INVALID_POSITION)
        {
           
            switch (ev.getAction())
            {
                case MotionEvent.ACTION_UP:
                    int upX = (int)ev.getX();  
                    int upY = (int)ev.getY(); 
                    stopDrag();
                    onDrop(upX,upY);
                    break;
          
                case MotionEvent.ACTION_MOVE:
                    int moveX = (int)ev.getX();                
                    int moveY = (int)ev.getY();
                    Log.d("ACTION_MOVE", "ACTION_MOVE x" + moveX + "ev.getRawx=" + ev.getRawX());
                    onDrag(moveX,moveY);
                    break;
          
            }
        }
        return super.onTouchEvent(ev);
    }
   
    private void onDrag(int x, int y)
    {
        if (dragImageView != null)
        {
            windowParams.alpha = 0.6f;
           
            // x 表示 相對於這個最邊緣 本身view的布局座標.
            // dragPointx 表示相對於item左邊的位置
            // dragoffsetX 表示布局相對於 螢幕(0,0)的位置
           
            // x-dragPointx = getLeft();
            // y-dragPonitY =getTop();
            windowParams.x = x - dragPointX + dragOffsetX;
            windowParams.y = y - dragPointY + dragOffsetY;
            windowManager.updateViewLayout(dragImageView, windowParams);
        }
    }
   
    private void onDrop(int x, int y)
    {
        int tempPosition = pointToPosition(x, y);
        if (tempPosition != AdapterView.INVALID_POSITION)
        {
            dropPosition = tempPosition;
        }
        if (dropPosition != dragPosition)
        {
            System.out.println("dragPosition: " + dragPosition + " dropPosition: " + dropPosition);
            ImageAdapter adapter = (ImageAdapter)this.getAdapter();
            adapter.exchange(dragPosition, dropPosition);
           
            // 解決問題3
            /*
             * ViewGroup itemView1 = (ViewGroup)getChildAt(dragPosition -
             * getFirstVisiblePosition()); ViewGroup itemView2 =
             * (ViewGroup)getChildAt(dropPosition - getFirstVisiblePosition());
             * itemView1.destroyDrawingCache(); itemView2.destroyDrawingCache();
             */
        }
    }
   
    private void stopDrag()
    {
        if (dragImageView != null)
        {
            windowManager.removeView(dragImageView);
            dragImageView = null;
        }
       
    }
   
}