recyclerVeiw的学习（二）

没有人在乎你在深夜痛哭，也没有人在乎你辗转反侧要熬几个秋。外人只看结果，自己独撑整个过程。等我们明白了这个道理，便不会再别人面前矫情，四处诉说以求宽慰

这篇文章主要来讲讲recyclerVeiw的item的滑动跟拖拽

先上图

策划与拖拽.gif

主要是重写ItemTouchHelper这个类，具体的实现的方法我在这里也注视了，最后将ItemTouchHelper跟recyclerView关联。

 itemTouchHelper = new ItemTouchHelper(new ItemTouchHelper.Callback() {
            //用于设置拖拽和滑动的方向
            @Override
            public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
                int dragFlags = 0, swipeFlags = 0;
                if (recyclerView.getLayoutManager() instanceof StaggeredGridLayoutManager || recyclerView.getLayoutManager() instanceof GridLayoutManager) {
                    dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN | ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT;
                } else if (recyclerView.getLayoutManager() instanceof LinearLayoutManager) {
                    dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN;
                    //设置侧滑方向为从左到右和从右到左都可以
                    swipeFlags = ItemTouchHelper.START | ItemTouchHelper.END;
                }
                return makeMovementFlags(dragFlags, swipeFlags);
            }

            //长摁item拖拽时会回调这个方法
            @Override
            public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
                int from = viewHolder.getAdapterPosition();
                int to = target.getAdapterPosition();
                Collections.swap(meiziList, from, to);
                mAdapter.notifyItemMoved(from, to);
                return true;
            }

            //这里处理滑动删除
            @Override
            public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
                mAdapter.removeItem(viewHolder.getAdapterPosition());
            }

            //当item拖拽开始时调用
            @Override
            public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState) {
                super.onSelectedChanged(viewHolder, actionState);
                if (actionState == ItemTouchHelper.ACTION_STATE_DRAG) {
                    viewHolder.itemView.setBackgroundColor(Color.LTGRAY);
                }
            }
            //当item拖拽完成时调用
            @Override
            public boolean isLongPressDragEnabled() {
                //不需要长按拖动，
                return true;
            }
            @Override
            public void clearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
                super.clearView(recyclerView, viewHolder);
                viewHolder.itemView.setBackgroundColor(Color.WHITE);
            }
            //当item视图变化时调用
            @Override
            public void onChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
                viewHolder.itemView.setAlpha(1 - Math.abs(dX) / screenwidth);
                //根据item滑动偏移的值修改item透明度。screenwidth是我提前获得的屏幕宽度
                super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
            }
        });
 itemTouchHelper.attachToRecyclerView(recycler);

当然平常开发中这些功能不是很常见

https://github.com/yanzhenjie/SwipeRecyclerView 这个是开发中很常见的策划实例