将B项目作为module导入A项目后，B项目的MainActivity中findviewbyid返回null

问题如题

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="5dp"
    tools:context=".MainActivity">




    <ExpandableListView
        android:id="@+id/lol_hero_list"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:childDivider="#dddddd"/>

</RelativeLayout>

  protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(com.example.expanedlist.R.layout.activity_main);
                lol_hero_list =(ExpandableListView)findViewById(R.id.lol_hero_list) ;
                ｝

https://blog.csdn.net/pathuang68/article/details/6702873