列表拖动排序功能也算是比较常见的了。在RecycleView还没有出现的那个年代，依稀记得是重写GridView实现拖拽，WindowManager实现拖拽的镜像。

不过，现在好了，有了RecycleView之后，一切都变得简单了。因为RecycleView提供了拖动的回调ItemTouchHelper.Callback，通过实现该类，会让我们少写很多代码。

先看一下，简化后的Demo效果图。

这里的实现的效果是：
① 第一个标签不可编辑
② 除了第一个标签外，其它标签可拖拽排序和删除

ItemTouchHelper.Callback的实现类

public class ItemDragCallback extends ItemTouchHelper.Callback {
    private ChannelAdapter mAdapter;
    private boolean mEdit;

    public ItemDragCallback(ChannelAdapter mAdapter) {
        this.mAdapter = mAdapter;
    }

    
    @Override
    public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
        ChannelAdapter adapter = (ChannelAdapter) recyclerView.getAdapter();
        mEdit = adapter.isEdit;
        //是否是编辑状态
        if (!mEdit) {
            return 0;
        }
        int position = viewHolder.getLayoutPosition();
        //第一个item不用交换
        if (position == 0) {
            return 0;
        }
        int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN | ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT;
        int swipeFlags = 0;
        return makeMovementFlags(dragFlags, swipeFlags);
    }

    @Override
    public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
        int fromPosition = viewHolder.getAdapterPosition();   //拖动的position
        int toPosition = target.getAdapterPosition();     //释放的position
        int position = viewHolder.getLayoutPosition();
        //第一个item不用交换
        if (position == 0) {
            return false;
        }
        mAdapter.itemMove(fromPosition, toPosition);
        return true;
    }

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

    }


    @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);
        if (dX != 0 && dY != 0 || isCurrentlyActive) {
            ChannelAdapter adapter = (ChannelAdapter) recyclerView.getAdapter();
            mEdit = adapter.isEdit;
        }
    }

    @Override
    public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState) {
        super.onSelectedChanged(viewHolder, actionState);
        if (actionState == ACTION_STATE_DRAG) {
            //长按时调用
            ChannelAdapter.ChannelHolder holder = (ChannelAdapter.ChannelHolder) viewHolder;
            holder.name.setBackgroundColor(Color.parseColor("#FDFDFE"));
            holder.name.setBackground(ContextCompat.getDrawable(ProjectApp.getApp(), R.drawable.shape_channel_bg));
            holder.delete.setVisibility(View.GONE);
        }
    }

    @Override
    public void clearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
        super.clearView(recyclerView, viewHolder);
        //松手时调用
        ChannelAdapter.ChannelHolder holder = (ChannelAdapter.ChannelHolder) viewHolder;
        holder.name.setBackground(ContextCompat.getDrawable(ProjectApp.getApp(), R.drawable.shape_channel_bg));
        holder.delete.setVisibility(View.VISIBLE);
    }
}

public class ChannelAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

    private Context mContext;
    private List<ChannelBean> mSortedList;
    public boolean isEdit;//是否是编辑状态

    public ChannelAdapter(Context mContext, List<ChannelBean> list) {
        this.mContext = mContext;
        mSortedList = list;
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(mContext).inflate(R.layout.item_channel, parent, false);
        return new ChannelHolder(view);
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        setChannel((ChannelHolder) holder, mSortedList.get(position));
    }


    private void setChannel(final ChannelHolder holder, final ChannelBean bean) {
        holder.name.setText(bean.getName());
        int position = holder.getLayoutPosition();
        //点击标签删除已选标签
        holder.name.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (!bean.isLock()) {
                    if (isEdit) {
                        removeFromSelected(holder);
                    }
                } else {
                }
            }
        });
        //长按进入编辑状态
        holder.name.setOnLongClickListener(new View.OnLongClickListener() {
            @Override
            public boolean onLongClick(View v) {
                    isEdit = true;
                    notifyDataSetChanged();
                //返回true 防止长按拖拽事件跟点击事件冲突
                return true;
            }
        });
        //点击X删除已选标签
        holder.delete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                removeFromSelected(holder);
            }
        });
        //是否是编辑状态且第一个不可编辑
        if (isEdit&&position!=0) {
            holder.delete.setVisibility(View.VISIBLE);
        } else {
            holder.delete.setVisibility(View.GONE);
        }
    }

    /**
     * 删除已选标签
     * @param holder
     */
    private void removeFromSelected(ChannelHolder holder) {
        int position = holder.getLayoutPosition();
        holder.delete.setVisibility(View.GONE);
        notifyItemRemoved(position);
        mSortedList.remove(position);
        notifyDataSetChanged();
    }

    /**
     * 对拖拽的元素进行排序
     * @param fromPosition
     * @param toPosition
     */
    void itemMove(int fromPosition, int toPosition) {
        if (fromPosition < toPosition) {
            for (int i = fromPosition; i < toPosition; i++) {
                Collections.swap(mSortedList, i, i + 1);
            }
        } else {
            for (int i = fromPosition; i > toPosition; i--) {
                Collections.swap(mSortedList, i, i - 1);
            }
        }
        notifyItemMoved(fromPosition, toPosition);
    }

    @Override
    public int getItemCount() {
        return mSortedList == null ? 0 : mSortedList.size();
    }

    class ChannelHolder extends RecyclerView.ViewHolder {
        TextView name;
        ImageView delete;

        public ChannelHolder(View itemView) {
            super(itemView);

            int validWidth = ScreenUtil.getScreenWidth() - Px2DpUtil.dp2px(mContext, 45);
            int childWidth = validWidth / 4;
            name = (TextView) itemView.findViewById(R.id.channel_name);
            FrameLayout.LayoutParams params = new FrameLayout.LayoutParams(childWidth, Px2DpUtil.dp2px(mContext, 35));
            params.setMargins(0, Px2DpUtil.dp2px(mContext, 5), 0, 0);
            name.setLayoutParams(params);
            name.setGravity(Gravity.CENTER);
            delete = (ImageView) itemView.findViewById(R.id.channel_delete);
        }
    }
}

调用就比较简单了

ItemDragCallback callback = new ItemDragCallback(mAdapter);
ItemTouchHelper helper = new ItemTouchHelper(callback);
helper.attachToRecyclerView(mRecyclerView);

到这里就结束了。