尝试从片段调用活动时出现ClassCastException

Question

我创建了片段，需要调用我从开发人员教程中引用的活动。但是以下代码：

public void onAttach(Activity activity) 
{

    super.onAttach(activity);
    try 
    {
        interfaceDataCommunicator = (InterfaceDataCommunicator) activity;
    }
    catch (ClassCastException e)
    {
        throw new ClassCastException(activity.toString()
                + " must implement InterfaceDataCommunicator");
    }

}

即使我在mainactivity中实现了这个接口，也会抛出classcastexception。我无法弄清楚原因。任何帮助都将非常感激。这就是我的主要活动：

public class TestActivity extends Activity implements InterfaceDataCommunicator
{
public InterfaceDataCommunicatorFromActivity interfaceDataCommunicatorFromActivity;
protected void onCreate(Bundle savedInstanceState) 
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_fragment);
}


public void updateData(String data)
{
     //interfaceDataCommunicatorFromActivity.updateData(data);
              this.data=data;
}