因为你还没有设置LinearLayoutManager为RecyclerView。

because you have not set LinearLayoutManager to RecyclerView.

例如：

    mRecyclerView = (RecyclerView) findViewById(R.id.recyclerView);
    LinearLayoutManager layoutManager = new LinearLayoutManager(context);
    mRecyclerView.setLayoutManager(layoutManager);
    mRecyclerView.setAdapter(new CustomAdapter());