方向更改后 FIndFragmentByTag 失败

Question

我正在尝试使用 UIless 保留 Fragment 在方向更改期间不丢失服务绑定器。问题是在onCreate Activity 中findFragmentByTag 总是返回null。

这是我的活动：

public abstract class AbstractLearnActivity extends Activity implements FragmentCallbacks {
    private final static String BINDER_FRAG_TAG = "AbstractLearnActivity.BINDER_FRAG_TAG";

    private BinderFragment binderFragment;

    @Override
    protected void onCreate(Bundle savedInstanceState){
        FragmentManager fm = getFragmentManager();
        //do some initialization stuff...

        Fragment fragment = fm.findFragmentByTag(BINDER_FRAG_TAG);
        if(fragment != null){
            Log.i("asd", "Binder Frag already exists");
            binderFragment = (BinderFragment)fragment;
        }
        else{
            Log.i("asd", "Binder frag is null");
            binderFragment = new BinderFragment();
            fm.beginTransaction().add(binderFragment, BINDER_FRAG_TAG).commit();
        }
        setContentView(R.layout.activity_main);
        super.onCreate(savedInstanceState);
    }
}

虽然这是片段：

public class BinderFragment extends Fragment {
    private Application application;

    public BinderFragment(){
        Log.i("asd", "Constructor called for binder fragment");
    }

    @Override
    public void onAttach(Activity activity){
        super.onAttach(activity);
        if(application == null){
            application = activity.getApplication();
            //make connections...
        }
    }

    @Override
    public void onCreate(Bundle savedInstanceState){
        setRetainInstance(true);
        super.onCreate(savedInstanceState);
    }

     @Override
     public void onDestroy(){
         Log.i("asd", "binder fragment destroyed");
         super.onDestroy();
         //disconnect services
     }
}

如果我运行应用程序并尝试改变我得到的方向：

<application started>
I/asd﹕ Binder frag is null
I/asd﹕ Constructor called for binder fragment
I/asd﹕ Attaching
<orientation change>
I/asd﹕ Is fragment found? true
I/asd﹕ Binder frag is null
I/asd﹕ Constructor called for binder fragment
I/asd﹕ Attaching
<orientation change>
I/asd﹕ Is fragment found? true
I/asd﹕ Binder frag is null
I/asd﹕ Constructor called for binder fragment
I/asd﹕ Attaching
<application closed>
I/asd﹕ binder fragment destroyed
I/asd﹕ binder fragment destroyed
I/asd﹕ binder fragment destroyed
I/asd﹕ Is fragment found? false

正如您所见，Fragment 在 Activity 被销毁时就在那里，并且它被正确保留（因为它们在应用程序关闭时都被销毁），但是 onCreate 找不到它并创建一个新的.. . 有人知道为什么我不能按标签检索片段吗？

感谢您的帮助^^

Answer 1

在这里拍一张，

为什么在 Fragment 事务提交后调用 super 和 setContentView。在onCreate方法中，先调用super再调用setContentView再分片事务。

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

        FragmentManager fm = getFragmentManager();
        //do some initialization stuff...

       FragmentManager fragmentManager = getFragmentManager(); //suggestion to use supportFragmentMan
       binderFragment = (BinderFragment) fragmentManager.findFragmentByTag(TAG_SEARCH_ARTIST_FRAGMENT);

       if(binderFragment == null){
            binderFragment = new BinderFragment();
            fragmentManager.beginTransaction().add(binderFragment , BINDER_FRAG_TAG).commit();
       } 
    }

希望这会有所帮助！