如何创建可拖放的RecyclerView（交换2个项目位置版本）

Question

我有一个使用滑动和拖放执行操作的ItemTouchHelper类。但是我想要改变拖放行为。它应该交换2个元素的位置，即我拖动的第一个元素和它放置的另一个元素。我想交换被拖动和投放位置的项目，而不是在它们之间更改所有项目的位置。

如何实现

这是我的拖放类:

public class ItemTouchHelper extends 
androidx.recyclerview.widget.ItemTouchHelper.Callback {

private Drawable icon;
private Context context;
private ColorDrawable background;
private final ItemTouchHelperListener dragDropListener;

public ItemTouchHelper(Context context, Drawable icon,
                       ItemTouchHelperListener dragDropListener) {
    this.icon = icon;
    this.dragDropListener = dragDropListener;
    this.context = context;
    this.background = new ColorDrawable(context.getResources().getColor(R.color.deleteItem));
}

@Override
public void onChildDraw(@NonNull Canvas c, @NonNull RecyclerView recyclerView,
                        @NonNull RecyclerView.ViewHolder viewHolder,
                        float dX, float dY,
                        int actionState, boolean isCurrentlyActive) {
    super.onChildDraw(c, recyclerView, viewHolder, dX,
            dY, actionState, isCurrentlyActive);
    View itemView = viewHolder.itemView;

    int iconMargin = (itemView.getHeight() - icon.getIntrinsicHeight()) / 2;
    int iconTop = itemView.getTop() + (itemView.getHeight() - icon.getIntrinsicHeight()) / 2;
    int iconBottom = iconTop + icon.getIntrinsicHeight();

    if (dX > 0) {
        background = new ColorDrawable(context.getResources().getColor(R.color.deleteItem));

        iconMargin = (itemView.getHeight() - icon.getIntrinsicHeight()) / 2;
        iconTop = itemView.getTop() + (itemView.getHeight() - icon.getIntrinsicHeight()) / 2;
        iconBottom = iconTop + icon.getIntrinsicHeight();

        int iconRight = itemView.getLeft() + iconMargin + icon.getIntrinsicWidth();
        int iconLeft = itemView.getLeft() + iconMargin;

        icon.setBounds(iconLeft, iconTop, iconRight, iconBottom);

        background.setBounds(itemView.getLeft(), itemView.getTop(),
                itemView.getLeft() + ((int) dX),
                itemView.getBottom());
    } else if (dX < 0) {
        int iconRight = itemView.getRight() - iconMargin;
        int iconLeft = itemView.getRight() - iconMargin - icon.getIntrinsicWidth();
        icon.setBounds(iconLeft, iconTop, iconRight, iconBottom);
        background.setBounds(itemView.getRight(), itemView.getTop(),
                itemView.getRight() + ((int) dX),
                itemView.getBottom());
    } else {
        background.setBounds(0, 0, 0, 0);
        icon.setBounds(0, 0, 0, 0);
    }

    background.draw(c);
    icon.draw(c);
}

@Override
public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder,
                     int direction) {
    dragDropListener.deleteElementDialog(viewHolder.getAdapterPosition());
}

@Override
public int getMovementFlags(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder) {
    int dragFlags = UP | DOWN;
    int swipeFlags = START | END;
    return makeMovementFlags(dragFlags, swipeFlags);
}

@Override
public boolean onMove(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder,
                      @NonNull RecyclerView.ViewHolder target) {
    dragDropListener.onRowMoved(viewHolder.getAdapterPosition(), target.getAdapterPosition());
    return true;
}

@Override
public void onSelectedChanged(RecyclerView.ViewHolder viewHolder,
                              int actionState) {
    if (actionState != ACTION_STATE_IDLE && actionState != ACTION_STATE_SWIPE) {
        dragDropListener.onRowSelected(viewHolder);
    }
    super.onSelectedChanged(viewHolder, actionState);
}

@Override
public void clearView(@NonNull RecyclerView recyclerView,
                      @NonNull RecyclerView.ViewHolder viewHolder) {
    super.clearView(recyclerView, Objects.requireNonNull(viewHolder));
    dragDropListener.onRowClear(Objects.requireNonNull(viewHolder));
}

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

}

这是我的ItemTouchHelperListener：

    public void setItemTouchHelperListener() {
    ItemTouchHelperListener itemTouchHelperListener = new 
   ItemTouchHelperListener() {
        @Override
        public void onRowMoved(int fromPosition, int toPosition) {
            presenter.rowMoved(fromPosition, toPosition);
        }

        @Override
        public void onRowSelected(RecyclerView.ViewHolder myViewHolder) {
            if (myViewHolder instanceof ElementsAdapter.ElementsViewHolder) {
                elementsAdapter.rowSelected((ElementsAdapter.ElementsViewHolder) myViewHolder);
                presenter.rowSelected(myViewHolder.getAdapterPosition());
            }
        }

        @Override
        public void onRowClear(RecyclerView.ViewHolder myViewHolder) {
            if (myViewHolder instanceof ElementsAdapter.ElementsViewHolder) {
                elementsAdapter.rowClear((ElementsAdapter.ElementsViewHolder) myViewHolder);
                presenter.rowClear(myViewHolder.getAdapterPosition());
            }
        }

        @Override
        public void deleteElementDialog(int adapterPosition) {
            createDeleteDialog(adapterPosition);
        }
    };

- Kratos

---

包含一个嵌入式视频演示或链接以展示您想要的行为会很有帮助。例如，“它被放置在哪里”这样的说法很难想象，因为通常被拖动的项目将悬挂在两个元素之间。 - Nerdy Bunz

Answer 1

我完全同意@Zain的答案，但是有一个问题，假设你想用第三个项目替换第一个项目，那么你需要点击并按住第三个项目，将其拖到第一个项目上方。一旦您放下，您会注意到第三个项目将再次移回其原始位置，然后两个项目都将得到正确更新。这看起来不好。

我稍微修改了@Zain的答案。

private int fromPos = -1;
private int toPos = -1;

ItemTouchHelper itemTouchHelper = new ItemTouchHelper(new 
ItemTouchHelper.SimpleCallback(
    ItemTouchHelper.UP | ItemTouchHelper.DOWN |
    ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT, 0) {

@Override
public boolean onMove(@NonNull RecyclerView recyclerView,
                      @NonNull RecyclerView.ViewHolder viewHolder,   
                      @NonNull RecyclerView.ViewHolder target) {
    toPos = target.getAdapterPosition();
    return false;
}

@Override
public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder,
                     int direction) {}

@Override
public void onSelectedChange(@NonNull RecyclerView.ViewHolder 
                           viewHolder, int actionState) {
    switch(actionState){
          case ItemTouchHelper.ACTION_STATE_DRAG:{
             fromPos = viewHolder.getAdapterPosition();
             break; 
          }

          case ItemTouchHelper.ACTION_STATE_IDLE: {
              //Execute when the user dropped the item after dragging.
              if(fromPos != -1 && toPos != -1      
                 && fromPos != toPos) {
               moveItem(fromPos, toPos);
               fromPos = -1;
               toPos = -1; 
           } 
           break;
        }
}

private void moveItem(int oldPos, int newPos) {
   Item temp = mItems.get(oldPos);
   mItems.set(oldPos, mItems.get(newPos));
   mItems.set(newPos, temp);
   mAdapter.notifyItemChanged(oldPos);
   mAdapter.notifyItemChanged(newPos);
}

- Ankit Chandora

Answer 2

您可以通过使用onMove()方法注册拖动的项目和使用clearView()方法注册放置的项目来实现此操作; 然后修改您的RecyclerView适配器的数据源，以便您可以使用一个临时项来存储拖动的项目; 然后将被拖动的项设置为已拖动的项; 最后在落下的项上放置临时项。

然后利用RecyclerView适配器notifyItemChanged()来更新这个变化的布局。请注意: 在这里，我禁用了滑动，因为您的问题主要涉及拖放。

final int[] oldPos = new int[1];
final int[] newPos = new int[1];
ItemTouchHelper itemTouchHelper = new ItemTouchHelper(new ItemTouchHelper.SimpleCallback(

        ItemTouchHelper.UP |
                ItemTouchHelper.DOWN |
                ItemTouchHelper.LEFT |
                ItemTouchHelper.RIGHT,
        0) {
    @Override
    public boolean onMove(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, @NonNull RecyclerView.ViewHolder target) {
        oldPos[0] = viewHolder.getAdapterPosition();
        newPos[0] = target.getAdapterPosition();
        return false;
    }

    @Override
    public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder, int direction) {

    }

    @Override
    public void clearView(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder) {
        super.clearView(recyclerView, viewHolder);
        moveItem(oldPos[0], newPos[0]);
    }
});


private void moveItem(int oldPos, int newPos) {
    Item temp = mItems.get(oldPos);
    mItems.set(oldPos, mItems.get(newPos));
    mItems.set(newPos, temp);
    mAdapter.notifyItemChanged(oldPos);
    mAdapter.notifyItemChanged(newPos);

}

The result

- Zain

---

Zain，我觉得你没有理解我的问题。我的代码现在就像你建议的那样工作。但是我不想这样做。我只想改变拖放项目的位置，而不改变它们之间所有元素的位置。 - Kratos

@Haris 请检查我的更新代码...现在它可以正常运行了。 - Zain