Can not generate binding source for inner class

[binhbt]

When i change MainActivity for testing
public class MainActivity extends AppCompatActivity {

@BindView(R.id.tv_content)
TextView tvContent;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Binding.bind(this);
}

@OnClick(R.id.bt_1)
void bt1Click(View v) {
    tvContent.setText("Button 1 Clicked");
}

@OnClick(R.id.bt_2)
void bt2Click(View v) {
    tvContent.setText("Button 2 Clicked");
}
public class TestActivity  extends AppCompatActivity{
    @BindView(R.id.tv_content)
    TextView tvContent;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Binding.bind(this);
    }
}

}
Have no file "MainActivity$TestActivity$Binding.java" is created.
How can I inject for inner class?