RecyclerView拖拽排序与滑动删除

RecyclerView 作为ListView、GridView的替代品，从它诞生开始就如火如荼，很多基于其改造的刷新、header控件应运而生，今天我们的主角是拖拽与删除效果，很多关于ListView拖拽、侧滑菜单的控件可能并不能移植到RecyclerView上，但作为继承物怎么能不支持拖拽与侧滑呢？
ItemTouchHelper便是一个用于处理RecyclerView拖拽与滑动删除的强大工具，可以轻而易举的支持几乎所有LayoutManager，并且支持item的动画等等。ItemTouchHelper在使用上也是非常的简单的，只需要新建ItemTouchHelper实例，然后attachToRecyclerView就可以了，是不是相当容易。

public class TouchCallBack extends ItemTouchHelper.Callback {
    ItemTouchHelperCallback callback;

    void setItemTouchHelperCallback(ItemTouchHelperCallback callback) {
        this.callback = callback;
    }

    @Override
    public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
        int dragFlag, swipeFlag = 0;
        if (recyclerView.getLayoutManager() instanceof GridLayoutManager) {
            dragFlag = ItemTouchHelper.UP | ItemTouchHelper.DOWN | ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT;
        } else {
            dragFlag = ItemTouchHelper.UP | ItemTouchHelper.DOWN;
            swipeFlag = ItemTouchHelper.START | ItemTouchHelper.END;
        }
        return makeMovementFlags(dragFlag, swipeFlag);
    }

    @Override
    public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
        int fromPosition = viewHolder.getAdapterPosition();
        int toPosition = target.getAdapterPosition();
        if (callback != null) {
            callback.onItemMove(fromPosition, toPosition);
        }
        return true;
    }

    @Override
    public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
        if (callback != null) {
            callback.onItemDismiss(viewHolder.getAdapterPosition());
        }
    }

    @Override
    public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState) {
        if (actionState != ItemTouchHelper.ACTION_STATE_IDLE) {
            viewHolder.itemView.setBackgroundColor(Color.LTGRAY);
        }
        super.onSelectedChanged(viewHolder, actionState);
    }

    @Override
    public void clearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
        super.clearView(recyclerView, viewHolder);
        viewHolder.itemView.setBackgroundColor(Color.TRANSPARENT);
    }

    public interface ItemTouchHelperCallback {
        void onItemMove(int fromPosition, int toPosition);

        void onItemDismiss(int position);
    }
}

• ItemTouchHelperCallback是我们自定义用于拖拽、删除的回调接口
• getMovementFlags指定支持拖拽、滑动的方向，使用helperItemTouchHelper.makeMovementFlags(int, int)来构造返回的flag
• onMove是拖拽的方法
• onSwiped是删除的方法
• isLongPressDragEnabled是否支持拖拽，默认true
• isItemViewSwipeEnabled是否支持滑动删除，默认true
• onSelectedChanged选中item时的方法，这里我们以示区别改变了背景
• clearView完成时的方法，这里我们把背景改成了透明

然后只需要简单的如下操作便可以了

TouchCallBack touchCallBack = new TouchCallBack();
touchCallBack.setItemTouchHelperCallback(new TouchCallBack.ItemTouchHelperCallback() {
    @Override
    public void onItemMove(int fromPosition, int toPosition) {
        Collections.swap(data, fromPosition, toPosition);
        adapter.notifyItemMoved(fromPosition, toPosition);
    }

    @Override
    public void onItemDismiss(int position) {
        data.remove(position);
        adapter.notifyItemRemoved(position);
    }
});
ItemTouchHelper touchHelper = new ItemTouchHelper(touchCallBack);
touchHelper.attachToRecyclerView(recyclerView);

效果如下

如果我们仅仅只是需要拖拽或者滑动删除大可不必继承ItemTouchHelper.Callback而继承ItemTouchHelper.SimpleCallback实现构造、onMove与onSwiped即可

比如我们有这个的需求并不是所有的item都支持拖拽与删除，那我们需要做一些改变，将 isLongPressDragEnabled，isItemViewSwipeEnabled返回false。
然后我们需要监听item的长按事件，再判断是否有拖拽、删除功能，最后手动调用 touchHelper.startDrag(ViewHolder viewHolder)和touchHelper.startSwipe(ViewHolder viewHolder)实现效果。
这里RecyclerView的事件使用liaoinstan的介绍的OnItemTouchListener事件完成。

public abstract class OnRecyclerTouchListener implements RecyclerView.OnItemTouchListener {
    private GestureDetectorCompat mGestureDetector;
    private RecyclerView recyclerView;

    public OnRecyclerTouchListener(RecyclerView recyclerView) {
        this.recyclerView = recyclerView;
        mGestureDetector = new GestureDetectorCompat(recyclerView.getContext(), new ItemTouchHelperGestureListener());
    }

    @Override
    public boolean onInterceptTouchEvent(RecyclerView rv, MotionEvent e) {
        mGestureDetector.onTouchEvent(e);
        return false;
    }

    @Override
    public void onTouchEvent(RecyclerView rv, MotionEvent e) {
        mGestureDetector.onTouchEvent(e);
    }

    @Override
    public void onRequestDisallowInterceptTouchEvent(boolean disallowIntercept) {
    }

    private class ItemTouchHelperGestureListener extends GestureDetector.SimpleOnGestureListener {
        @Override
        public boolean onSingleTapUp(MotionEvent e) {
            View child = recyclerView.findChildViewUnder(e.getX(), e.getY());
            if (child != null) {
                RecyclerView.ViewHolder vh = recyclerView.getChildViewHolder(child);
                onItemClick(vh);
            }
            return true;
        }

        @Override
        public void onLongPress(MotionEvent e) {
            View child = recyclerView.findChildViewUnder(e.getX(), e.getY());
            if (child != null) {
                RecyclerView.ViewHolder vh = recyclerView.getChildViewHolder(child);
                onItemLongClick(vh);
            }
        }

        @Override
        public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
            View child = recyclerView.findChildViewUnder(e1.getX(), e1.getY());
            if (Math.abs(distanceX) > 0 && distanceY == 0) {
                if (child != null) {
                    RecyclerView.ViewHolder vh = recyclerView.getChildViewHolder(child);
                    onSideSlip(vh);
                }
            }
            return super.onScroll(e1, e2, distanceX, distanceY);
        }
    }

    public abstract void onItemClick(RecyclerView.ViewHolder vh);

    public abstract void onItemLongClick(RecyclerView.ViewHolder vh);

    public abstract void onSideSlip(RecyclerView.ViewHolder vh);
}

我们添加了三个抽象方法，用单击、长按、侧滑的回调，然后通过监听手势动作，调用相应的方法，然后我们把下面两个方法返回FALSE

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

最后给RecyclerView添加事件

recyclerView.addOnItemTouchListener(new OnRecyclerTouchListener(recyclerView) {
    @Override
    public void onItemClick(RecyclerView.ViewHolder vh) {

    }

    @Override
    public void onItemLongClick(RecyclerView.ViewHolder vh) {
        touchHelper.startDrag(vh);
    }

    @Override
    public void onSideSlip(RecyclerView.ViewHolder vh) {
        touchHelper.startSwipe(vh);
    }
});

这样我们可以通过条件判断手动调用拖拽与侧滑的方（这里直接调用了，我们可以根据实际情况添加判断）。
到这里ItemTouchHelper关于拖拽与侧滑的操作基本完成，当然我们还可以覆盖着两个方法

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

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

添加一些交互的动画，让操作更人性化，例如侧滑删除时改变item的透明度、或者添加滑动删除的提示，拖拽时添加长按下去的动画等等。更多操作请查看https://github.com/iPaulPro/Android-ItemTouchHelper-Demo

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