无法解析方法'add（com.cnh.phoneapp.view.OnGoingCallScreen，null）

Question

遇到错误，无法解决方法'add（com.cnh.phoneapp.view.OnGoingCallScreen，null）

import android.app.Activity;
    @Before
    public void setUp() throws Exception {
        OnGoingCallScreen onGoingCallScreen = new OnGoingCallScreen();
        Activity fragmentActivity;
        fragmentActivity = Robolectric.buildActivity(Activity.class).create().get();
        fragmentActivity.getFragmentManager().beginTransaction().add(onGoingCallScreen,null).commit();
    }

OnGoingCallScreen.java （片段是“ android.support.v4.app.Fragment.java）

public class OnGoingCallScreen extends Fragment{
......................
......................
}