不幸的是，当我想推送片段时，Android已停止

如果我想在用户选择菜单的某些元素（Android导航抽屉）时更改片段，我的应用程序将崩溃。

这是我的片段类代码

@SuppressLint("NewApi")
public class InboxActivity extends Fragment
{
    @Override

    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        return inflater.inflate(R.layout.inbox_fragment, container, false);

    }

}

这是非常简单的代码。

这是我在带抽屉的主班上所做的事情：

private void selectItem(int position) {


    Fragment f;
    if(position == 1)
    {
        f = new InboxActivity();
        FragmentManager fragmentManager = getFragmentManager();
        FragmentTransaction ft = fragmentManager.beginTransaction();
        ft.replace(R.id.content_frame, f);
        ft.commit();

        Intent activity = new Intent(getApplicationContext(), InboxActivity.class);
        startActivity(activity);                
    }
}

这也是非常简单的代码。这是我的错误：

04-22 11:18:25.830: E/AndroidRuntime(25512): FATAL EXCEPTION: main
04-22 11:18:25.830: E/AndroidRuntime(25512): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.android.navigationdrawerexample/com.example.android.navigationdrawerexample.InboxActivity}: java.lang.ClassCastException: com.example.android.navigationdrawerexample.InboxActivity cannot be cast to android.app.Activity
04-22 11:18:25.830: E/AndroidRuntime(25512):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
04-22 11:18:25.830: E/AndroidRuntime(25512):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2299)
04-22 11:18:25.830: E/AndroidRuntime(25512):    at android.app.ActivityThread.access$700(ActivityThread.java:154)
04-22 11:18:25.830: E/AndroidRuntime(25512):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1284)
04-22 11:18:25.830: E/AndroidRuntime(25512):    at android.os.Handler.dispatchMessage(Handler.java:99)
04-22 11:18:25.830: E/AndroidRuntime(25512):    at android.os.Looper.loop(Looper.java:137)
04-22 11:18:25.830: E/AndroidRuntime(25512):    at android.app.ActivityThread.main(ActivityThread.java:5306)
04-22 11:18:25.830: E/AndroidRuntime(25512):    at java.lang.reflect.Method.invokeNative(Native Method)
04-22 11:18:25.830: E/AndroidRuntime(25512):    at java.lang.reflect.Method.invoke(Method.java:511)
04-22 11:18:25.830: E/AndroidRuntime(25512):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
04-22 11:18:25.830: E/AndroidRuntime(25512):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
04-22 11:18:25.830: E/AndroidRuntime(25512):    at dalvik.system.NativeStart.main(Native Method)
04-22 11:18:25.830: E/AndroidRuntime(25512): Caused by: java.lang.ClassCastException: com.example.android.navigationdrawerexample.InboxActivity cannot be cast to android.app.Activity
04-22 11:18:25.830: E/AndroidRuntime(25512):    at android.app.Instrumentation.newActivity(Instrumentation.java:1071)
04-22 11:18:25.830: E/AndroidRuntime(25512):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2166)
04-22 11:18:25.830: E/AndroidRuntime(25512):    ... 11 more

我究竟做错了什么？