android - 如何通过长按项目在 ListView 中执行项目拖放

Question

我有一个 ListView，其中有一个图像作为项目列表。现在我想在 ListView 中执行拖放项目。因此，为此，我创建了一个扩展 ListView 的类“DragNDropListView”，并覆盖此类中 ListView 的 onTouch() 方法并执行拖放操作，它工作正常。

但我的要求是在长按 ListView 中的图像时拖放项目。那么如何做到这一点。我应该做与我在 ListView 的 onTouch() 方法中所做的相同的事情，还是应该修改此方法。

请帮我解决这个问题。

我的代码 onTouch 方法

@Override
public boolean onTouchEvent(MotionEvent ev) 
{
    final int action = ev.getAction();
    final int x = (int) ev.getX();
    final int y = (int) ev.getY();  
    
    if (action == MotionEvent.ACTION_DOWN) 
    {
        mDragMode = true;
    }

    if (!mDragMode) 
        return super.onTouchEvent(ev);

    switch (action) 
    {
        case MotionEvent.ACTION_DOWN:
        mStartPosition = pointToPosition(x,y);
        if (mStartPosition != INVALID_POSITION) 
        {
            int mItemPosition = mStartPosition - getFirstVisiblePosition();
            mDragPointOffset = y - getChildAt(mItemPosition).getTop();
            mDragPointOffset -= ((int)ev.getRawY()) - y;
            startDrag(mItemPosition,y);
            drag(0,y);// replace 0 with x if desired
        }   
        break;
        
        case MotionEvent.ACTION_MOVE:
        {
            drag(0,y);// replace 0 with x if desired
        }
        break;
        
        case MotionEvent.ACTION_CANCEL:             
        case MotionEvent.ACTION_UP:
        
        default:
        mDragMode = false;
        mEndPosition = pointToPosition(x,y);
        stopDrag(mStartPosition - getFirstVisiblePosition());
        if (mDropListener != null && mStartPosition != INVALID_POSITION && mEndPosition != INVALID_POSITION) 
             mDropListener.onDrop(mStartPosition, mEndPosition);
        break;
    }
    return true;
}   

// move the drag view
private void drag(int x, int y) 
{
    if (mDragView != null) 
    {
        WindowManager.LayoutParams layoutParams = (WindowManager.LayoutParams) mDragView.getLayoutParams();
        layoutParams.x = x;
        layoutParams.y = y - mDragPointOffset;
        WindowManager mWindowManager = (WindowManager) getContext()
                .getSystemService(Context.WINDOW_SERVICE);
        mWindowManager.updateViewLayout(mDragView, layoutParams);

        if (mDragListener != null)
            mDragListener.onDrag(x, y, null);// change null to "this" when ready to use
    }
}

// enable the drag view for dragging
private void startDrag(int itemIndex, int y) 
{
    stopDrag(itemIndex);

    View item = getChildAt(itemIndex);
    if (item == null) return;
    item.setDrawingCacheEnabled(true);
    if (mDragListener != null)
        mDragListener.onStartDrag(item);
    
    // Create a copy of the drawing cache so that it does not get recycled
    // by the framework when the list tries to clean up memory
    Bitmap bitmap = Bitmap.createBitmap(item.getDrawingCache());
    
    WindowManager.LayoutParams mWindowParams = new WindowManager.LayoutParams();
    mWindowParams.gravity = Gravity.TOP;
    mWindowParams.x = 0;
    mWindowParams.y = y - mDragPointOffset;

    mWindowParams.height = WindowManager.LayoutParams.WRAP_CONTENT;
    mWindowParams.width = WindowManager.LayoutParams.WRAP_CONTENT;
    mWindowParams.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
            | WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE
            | WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON
            | WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN
            | WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS;
    mWindowParams.format = PixelFormat.TRANSLUCENT;
    mWindowParams.windowAnimations = 0;
    
    Context context = getContext();
    ImageView v = new ImageView(context);
    v.setImageBitmap(bitmap);      

    WindowManager mWindowManager = (WindowManager)context.getSystemService(Context.WINDOW_SERVICE);
    mWindowManager.addView(v, mWindowParams);
    mDragView = v;
}

// destroy drag view
private void stopDrag(int itemIndex) 
{
    if (mDragView != null) {
        if (mDragListener != null)
            mDragListener.onStopDrag(getChildAt(itemIndex));
        mDragView.setVisibility(GONE);
        WindowManager wm = (WindowManager)getContext().getSystemService(Context.WINDOW_SERVICE);
        wm.removeView(mDragView);
        mDragView.setImageDrawable(null);
        mDragView = null;
    }
}   

用于听众

    ListView listView = getListView();

    if (listView instanceof DragNDropListView) 
    {
        ((DragNDropListView) listView).setDropListener(mDropListener);
        ((DragNDropListView) listView).setRemoveListener(mRemoveListener);
        ((DragNDropListView) listView).setDragListener(mDragListener);
    }

private DropListener mDropListener = new DropListener() 
{
    public void onDrop(int from, int to) 
    {
        ListAdapter adapter = getListAdapter();
        if (adapter instanceof ListViewAdapter) 
        {
            ((ListViewAdapter)adapter).onDrop(from, to);
            getListView().invalidateViews();
        }
    }
};

private RemoveListener mRemoveListener = new RemoveListener() 
{
    public void onRemove(int which) 
    {
        ListAdapter adapter = getListAdapter();
        if (adapter instanceof ListViewAdapter) {
            ((ListViewAdapter)adapter).onRemove(which);
            getListView().invalidateViews();
        }
    }
};


private DragListener mDragListener = new DragListener() 
{
    public void onDrag(int x, int y, ListView listView)
    {
    }

    public void onStartDrag(View itemView) 
    {
        itemView.setVisibility(View.INVISIBLE);
        ImageView iv = (ImageView)itemView.findViewById(R.id.image);
        if (iv != null) iv.setVisibility(View.VISIBLE);
    }

    public void onStopDrag(View itemView) 
    {
        itemView.setVisibility(View.VISIBLE);
        ImageView iv = (ImageView)itemView.findViewById(R.id.image);
        if (iv != null) iv.setVisibility(View.VISIBLE);
    }
    
};

Answer 1

是的，您可以简单地使用一些监听器来监听您的 ListView -

public interface DropListener {

/**
 * Called when an item is to be dropped.
 * @param from - index item started at.
 * @param to - index to place item at.
 */
    void onDrop(int from, int to);
}

试着看看这个Example.