在回收者视图

Question

我正在使用recyclerview和网格布局管理器。 Recyclerview项目需要在某些基础上进行分组。因为分组，每一行可以有不同的列数。

例如 - row1总共可以有4个项目，第2行只能有1个项目，依此类推。

现在我想实现拖放功能。 任何物品都可以拖到任何地方，也可以用其他物品替换，也可以将它拖到某些物品的左侧或右侧，或者拖到两个物品之间。

因此，拖放后，有4个项目的第1行现在可能有5个项目。

但是我可以实现的是将它们相互替换，而不是在视图之间。

我尝试过的代码：

public class ItemTouchHelperCallback extends ItemTouchHelper.Callback {

        private final ItemTouchHelperAdapter mAdapter;

        public ItemTouchHelperCallback(ItemTouchHelperAdapter adapter) {
                mAdapter = adapter;
        }

        @Override
        public boolean isLongPressDragEnabled() {
                return true;
        }

        @Override
        public boolean isItemViewSwipeEnabled() {
                return false;
        }

        @Override
        public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
                // Set movement flags based on the layout manager
                final int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN | ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT;
                final int swipeFlags = 0;
                return makeMovementFlags(dragFlags, swipeFlags);
        }

        @Override
        public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder source, RecyclerView.ViewHolder target) {
                // Notify the adapter of the move
                mAdapter.onItemMove(source.getAdapterPosition(), target.getAdapterPosition());
                return true;
        }

    When a dragging View overlaps multiple other views, Callback chooses the closest View with which dragged View might have changed positions. Although this approach works for many use cases, if you have a custom LayoutManager, you can override `chooseDropTarget(ViewHolder, java.util.List, int, int)` to select a custom drop target.




//  Return true if the current ViewHolder can be dropped over the the target ViewHolder.
        @Override
        public boolean canDropOver(RecyclerView recyclerView, RecyclerView.ViewHolder current, RecyclerView.ViewHolder target) {
                return super.canDropOver(recyclerView, current, target);
        }

        @Override
        public RecyclerView.ViewHolder chooseDropTarget(RecyclerView.ViewHolder selected, List<RecyclerView.ViewHolder> dropTargets, int curX, int curY) {
                return super.chooseDropTarget(selected, dropTargets, curX, curY);
        }

        @Override
        public int convertToAbsoluteDirection(int flags, int layoutDirection) {
                Log.i("flags",""+flags + " "+ ""+layoutDirection);
                return super.convertToAbsoluteDirection(flags, layoutDirection);
        }

        @Override
        public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
                // Notify the adapter of the dismissal

                Log.i("onSwiped","method");
                int position = viewHolder.getAdapterPosition();

                if (direction == ItemTouchHelper.LEFT){
                        Log.i("direction","left");
                    //  adapter.removeItem(position);
                }  if(direction == ItemTouchHelper.RIGHT){
                        Log.i("direction","right");
                }  if(direction == ItemTouchHelper.UP){
                        Log.i("direction","up");
                } if(direction == ItemTouchHelper.DOWN){
                        Log.i("direction","down");
                }

        }

        @Override
        public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState) {
                // We only want the active item to change
                if (actionState != ItemTouchHelper.ACTION_STATE_IDLE) {
                        if (viewHolder instanceof ItemTouchHelperViewHolder) {
                                // Let the view holder know that this item is being moved or dragged
                                ItemTouchHelperViewHolder itemViewHolder = (ItemTouchHelperViewHolder) viewHolder;
                                itemViewHolder.onItemSelected();
                        }
                }
                super.onSelectedChanged(viewHolder, actionState);
        }

        @Override
        public void clearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
                super.clearView(recyclerView, viewHolder);
                if (viewHolder instanceof ItemTouchHelperViewHolder) {
                        // Let the view holder know that this item is being moved or dragged
                        ItemTouchHelperViewHolder itemViewHolder = (ItemTouchHelperViewHolder) viewHolder;
                        itemViewHolder.onItemReleased();
                }
                mAdapter.onClearView();
        }

        @Override
        public void onChildDraw(Canvas c, RecyclerView recyclerView,
                                                        RecyclerView.ViewHolder viewHolder, float dX, float dY,
                                                        int actionState, boolean isCurrentlyActive) {

                if (actionState == ItemTouchHelper.ACTION_STATE_SWIPE) {
                        float width = (float) viewHolder.itemView.getWidth();
                        float alpha = 1.0f - Math.abs(dX) / width;
                        viewHolder.itemView.setAlpha(alpha);
                        viewHolder.itemView.setTranslationX(dX);
                } else {
                        super.onChildDraw(c, recyclerView, viewHolder, dX, dY,
                                actionState, isCurrentlyActive);
                }
        }

}

并在适配器中：

public boolean onItemMove(int fromPos, int toPos) {


                fromPosition = fromPos - 1;
                toPosition = toPos - 1;

                return true;
        }

        @Override
        public void onClearView() {


                if (fromPosition != toPosition) {
                        //some code
                }

                notifyDataSetChanged();
        }