自定义RecycleView上下拉刷新时，遇到的坑？

先上效果嘛？再讲遇到的问题

但在代码中，如果不加一行一个行分割器，就无法进下拉刷新。(PS:这个问题排查了两天，一直在找出现问题的地方，最后是无意发现的，项目中的代码里面没有加装饰器类。哭了很久啊)

        // 初始化商品类标签
        mRecyclerView = (MenuRecyclerView) container.findViewById(R.id.recycler_view);
        LinearLayoutManager manager = new LinearLayoutManager(container.getContext());
        manager.setOrientation(LinearLayoutManager.VERTICAL);
        mRecyclerView.setLayoutManager(manager);
        mRecyclerView.setOnRefreshViewListener(this);
        // 这一行很关键，如果不加上去，就无法进行下拉刷新等操作
        mRecyclerView.addItemDecoration(new DividerItemDecoration(container.getContext(), DividerItemDecoration.VERTICAL));


        // 增加一个空的界面
        View emptyView = container.findViewById(R.id.layout_empty);
        mRecyclerView.setEmptyView(emptyView);
        TextView textView = (TextView) emptyView.findViewById(R.id.text_empty);
        textView.setText("暂无数据");
        textView.setTextColor(getResources().getColor(R.color.gray_label));


        // 绑定数据
        mAdapter = new MessagePeopleAdapter(container.getContext(), data, true);
        mAdapter.setOnItemClickListener(this);
        mAdapter.setOnMenuItemClickListener(this);
        mRecyclerView.setAdapter(mAdapter);

运行结果如下：

 // 滑动 header
    private void moveHeader(MotionEvent e){
        int x = (int) e.getX();
        int y = (int) e.getY();

        switch (e.getAction()) {
            case MotionEvent.ACTION_DOWN:
                isOnTouching = true;
                break;
            case MotionEvent.ACTION_MOVE:
                //判断是否滑动到了头部
                Log.e("TAG", "判断是否滑动到了头部:"+canScrollVertically(-1));
                if (!canScrollVertically(-1)) {
                    int dy = lastY - y;
                    int dx = lastX - x;

                    if (Math.abs(dy) > Math.abs(dx)) {
                        isRefresh = true;
                        changeHeight(dy);
                    }
                }
                break;
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_CANCEL:
                isRefresh = false;
                isOnTouching = false;
                if (mState == STATE_READY) {
                    onStatusChange(STATE_REFRESHING);
                }
                autoSize();
                break;
        }

        lastX = x;
        lastY = y;

    }

正确结果

如果不加分割装饰器类的话，就一直表示未滑动到顶部。

最后查看了一下，源代码：

其中

// 这一行很关键，如果不加上去，就无法进行下拉刷新等操作
mRecyclerView.addItemDecoration(new DividerItemDecoration(container.getContext(), DividerItemDecoration.VERTICAL));

主要调用到了下面这个函数 isComputingLayout 返回true表示lockdown锁定状态下，adapter的更新将不再更新RecylerView的layout大小。不太了解的情况下，使用该方法，很坑的

 /**

     * Returns whether RecyclerView is currently computing a layout.
     * 

     * If this method returns true, it means that RecyclerView is in a lockdown state and any
     * attempt to update adapter contents will result in an exception because adapter contents
     * cannot be changed while RecyclerView is trying to compute the layout.
     * 

     * It is very unlikely that your code will be running during this state as it is
     * called by the framework when a layout traversal happens or RecyclerView starts to scroll
     * in response to system events (touch, accessibility etc).
     * 

     * This case may happen if you have some custom logic to change adapter contents in
     * response to a View callback (e.g. focus change callback) which might be triggered during a
     * layout calculation. In these cases, you should just postpone the change using a Handler or a
     * similar mechanism.
     *
     * @return true if RecyclerView is currently computing a layout, false
     *         otherwise
     */
    public boolean isComputingLayout() {
        return mLayoutOrScrollCounter > 0;
    }