Can not setContentView with layout resource file

Can not setContentView with layout resource file

A Package named "ui" is created in the package layout, and the layout
resource file "my_listview.xml" is put in the package "ui". I would like
to setContentView with "my_listview.xml" in the MainActiviy.java, but
failed. What's the problem here? Any help will be appreciated.
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.my_listview);
...
}