java - RecyclerView 拖放式 - 文件和文件夹

Question

现在我正在使用 RecyclerView 的 ItemTouchHelper.Callback 来重新排列我的回收站 View 中项目的位置。

但现在我需要的是文件和文件夹的功能。

场景是文件和文件夹都是同一个回收器 View 的项目。现在，当我将一个项目拖到一个文件夹上时，该文件夹不应从其位置移动，而是应该接受源 View 持有者作为其自身的子级。并且在其上释放一个项目时，源 View 持有者被隐藏并从回收者 View 中删除。虽然文件夹仍然存在。

我在谷歌上搜索了很多，但没能为 Recycler View 找到此类行为的单一实现。

如果有人指导我应该处理什么，以获得此功能。

谢谢。

Answer 1

使用 ItemTouchHelper.SimpleCallback。它扩展了 ItemTouchHelper.Callback，所以您可以用同样的方式将它附加到 RecyclerView。

您可以使用 ItemTouchHelper.SimpleCallback 提供的项目拖动的默认功能。您还可以获得一些通知，这些通知将允许您实现放入文件夹。

下面的类(class)将演示如何更改文件夹的背景颜色。一个项目将被放入该文件夹。

您应该在所描述的位置添加用于重新排序和删除项目的代码(例如在数据库中)。

class ItemDragAndDropCallback extends ItemTouchHelper.SimpleCallback {

    private final RecyclerView recyclerView;

    ItemDragAndDropCallback(RecyclerView recyclerView) {
        // Choose drag and swipe directions
        // Up and down is chosen for dragging
        // Nothing is chosen for swiping
        super(ItemTouchHelper.UP | ItemTouchHelper.DOWN, 0);
        this.recyclerView = recyclerView;
    }

    @Override
    public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
        int from = viewHolder.getAdapterPosition();
        int to = target.getAdapterPosition();
        // You can reorder items here
        // Reorder items only when target is not a folder
        recyclerView.getAdapter().notifyItemMoved(from, to);
        return true;
    }

    @Override
    public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
        // You can react for swiping items here
        // Do nothing in your case
    }

    // An item will be dropped into this folder
    private View folder;

    @Override
    public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState) {
        super.onSelectedChanged(viewHolder, actionState);

        if (actionState == ItemTouchHelper.ACTION_STATE_DRAG) {

            // Here you are notified that the drag operation began

            if (folder != null) {
                folder.setBackgroundResource(0); // Clear former folder background
                folder = null;
            }
        } else if (actionState == ItemTouchHelper.ACTION_STATE_IDLE) {

            // Here you are notified that the last operation ended

            if (folder != null) {
                // Set folder background to a color indicating
                // that an item was dropped into it
                folder.setBackgroundColor(
                    ContextCompat.getColor(
                        recyclerView.getContext(), android.R.color.holo_green_dark
                    )
                );
                // You can remove item from the list here and add it to the folder
                // Remember to notify RecyclerView about it
                recyclerView.getAdapter().notifyItemRemoved(viewHolder.getAdapterPosition());
            }
        }
    }

    // This method gets called a lot, so don't do any expensive operations here
    @Override
    public void onChildDraw(
        Canvas c,
        RecyclerView recyclerView,
        RecyclerView.ViewHolder viewHolder,
        float dX,
        float dY,
        int actionState,
        boolean isCurrentlyActive
    ) {
        if (actionState == ItemTouchHelper.ACTION_STATE_DRAG && isCurrentlyActive) {

            // Here you are notified that the drag operation is in progress

            if (folder != null) {
                folder.setBackgroundResource(0); // Clear former folder background
                folder = null;
            }

            float itemActualPosition = viewHolder.itemView.getTop() + dY + viewHolder.itemView.getHeight() / 2;

            // Find folder under dragged item
            for (int i = 0; i < recyclerView.getChildCount(); i++) {
                View child = recyclerView.getChildAt(i);

                // Exclude dragged item from detection
                if (!child.equals(viewHolder.itemView)) {

                    // Accept folder which encloses item position
                    if (child.getTop() < itemActualPosition && itemActualPosition < child.getBottom()) {

                        folder = child;
                        // Set folder background to a color indicating
                        // that an item will be dropped into it upon release
                        folder.setBackgroundColor(
                            ContextCompat.getColor(
                                recyclerView.getContext(), android.R.color.holo_green_light
                            )
                        );
                        break;
                    }
                }
            }
        }
        super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
    }
}

当您将项目拖到文件夹上时，项目下的文件夹背景将为浅绿色。当您将项目放入文件夹时，其背景将为深绿色。