recyclerview 动态添加item之间的间距

在代码中动态添加recyclerview的item之间的间距
在初始化recyclerview的时候动态设置代码如下

mRecyclerView.setNestedScrollingEnabled(false);//关闭嵌套滑动
        mRecyclerView.addItemDecoration(new RecyclerView.ItemDecoration() {
            @Override
            public void getItemOffsets(Rect outRect, View view, RecyclerView parent, 
            RecyclerView.State state) {
                //设置距离为20dp
                outRect.top = 20;
            }
        });

效果图