Facebook Android SDK：爲什麼在調用Fragment的onActivityResult之前重新創建Activity？

Question

我寫了一個Fragment來管理Facebook登錄/登出Facebook Android SDK 3.5.2，下面的例子是here。

當通過Facebook Web部件的登錄過程完成後，MainActivity再次啓動（調用onCreate）。

然後在如果savedInstanceState!=null在MainActivity的onCreate，則savedInstanceState檢查或知道如果現有FacebookPrefsFragment實例必須恢復，如果必須創建一個新的實例示例代碼：

if (savedInstanceState == null) { 
    // Add the fragment on initial activity setup 
    mainFragment = new MainFragment(); 
    getSupportFragmentManager() 
    .beginTransaction() 
    .add(android.R.id.content, mainFragment) 
    .commit(); 
} else { 
    // Or set the fragment from restored state info 
    mainFragment = (MainFragment) getSupportFragmentManager() 
    .findFragmentById(android.R.id.content); 
} 

我的問題是我的MainActivity有很多Fragments，並且savedInstanceState不僅可以在Facebook登錄過程中不爲空。所以我有兩個問題：

• 爲什麼在Facebook登錄過程後再次創建MainActivity？不應該僅僅調用FacebookPrefsFragment的onActivityResult？

• 如果它將被創建，我怎麼能知道這是因爲Facebook SDK調用它？

MainActivity

public class MainActivity extends FragmentActivity { 

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

     if (savedInstanceState != null) {  

      // If the Activity has been started after the Facebook login process, restart the FacebookPrefsFragment, 
      // but how can I be sure that MainActivity has been called by the Facebook app? 

      FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction(); 
      Fragment facebookPrefsFragment = new FacebookPrefsFragment();  
      fragmentTransaction.replace(R.id.content_container, facebookPrefsFragment, "facebookPrefsFragment"); 
      fragmentTransaction.commit(); 
     } 
     else{ 
      // start other Fragment 
     } 
    } 

    // ... 
} 

FacebookPrefsFragment

public class FacebookPrefsFragment extends Fragment{ 

    private void onSessionStateChange(Session session, SessionState state, Exception exception) { 
     if (state.isOpened()) { 
      Log.i(this.getClass().getSimpleName(), "Logged in", MyApplication.LOG_LEVEL); 
     } else if (state.isClosed()) { 
      Log.i(this.getClass().getSimpleName(), "Logged out", MyApplication.LOG_LEVEL); 
     } 
    } 

    private Session.StatusCallback callback = new Session.StatusCallback() { 
     @Override 
     public void call(Session session, SessionState state, Exception exception) { 
      onSessionStateChange(session, state, exception); 
     } 
    }; 

    private UiLifecycleHelper uiHelper; 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 

     View view = inflater.inflate(R.layout.facebook_prefs, container, false); 

     LoginButton authButton = (LoginButton) view.findViewById(R.id.authButton); 
     authButton.setPublishPermissions(Arrays.asList("publish_actions")); 
     authButton.setFragment(this); 

     return view; 
    } 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     uiHelper = new UiLifecycleHelper(getActivity(), callback); 
     uiHelper.onCreate(savedInstanceState); 
    } 

    @Override 
    public void onResume() { 
     super.onResume(); 

     Session session = Session.getActiveSession(); 
     if (session != null && 
       (session.isOpened() || session.isClosed())) { 
      onSessionStateChange(session, session.getState(), null); 
     } 

     uiHelper.onResume(); 
    } 

    @Override 
    public void onActivityResult(int requestCode, int resultCode, Intent data) { 
     super.onActivityResult(requestCode, resultCode, data); 
     uiHelper.onActivityResult(requestCode, resultCode, data); 
    } 

    @Override 
    public void onPause() { 
     super.onPause(); 
     uiHelper.onPause(); 
    } 

    @Override 
    public void onDestroy() { 
     super.onDestroy(); 
     uiHelper.onDestroy(); 
    } 

    @Override 
    public void onSaveInstanceState(Bundle outState) { 
     super.onSaveInstanceState(outState); 
     uiHelper.onSaveInstanceState(outState); 
    } 
} 

Answer 1

哎呀，我發現爲什麼MainActivity是每次都重新創建的：這是因爲我可以在手機上激活「不要保留活動」選項！現在我必須找出在這種情況下該怎麼做...

Answer 2

你需要玩的

@Override 
    public void onActivityResult(int requestCode, int resultCode, Intent data) { 
     super.onActivityResult(requestCode, resultCode, data); 
     uiHelper.onActivityResult(requestCode, resultCode, data); 
    } 

查看應用程序來源時的請求代碼是什麼。 來源：https://github.com/facebook/facebook-android-sdk/blob/master/facebook/src/com/facebook/widget/FacebookDialog.java#L210

我測試了幾個月後，requestCode是什麼，你可以用來確定是否應用程序是從Facebook返回或沒有。

[編輯]

這是一個醜陋的黑客攻擊，但如果requestCode == 64206那麼你的活動剛剛從Facebook的回來。

Answer 3

這篇文章有點過時，但我想我會在這裏留下任何人遇到我遇到的問題。當本機Facebook應用程序未安裝時，我的應用程序正在重新創建，並且即使我擁有正確的請求代碼和數據，callbackManager.onActivityResult（）仍然返回false。我可以通過復位和回顧，如果初始調用返回false下面來解決這個問題：

facebookButton.registerCallback(callbackManager, Activity.this); 
callbackManager.onActivityResult(requestCode, resultCode, data);