findFragmentByTag（）返回null

Question

我不明白爲什麼findFragmentByTag（）在我的代碼中返回null。 我對我的片段onCreate（）有setRetainInstance（true），我使用getSupportFragmentManager（）。findFragmentByTag（），因爲它的SherlockFragmentActivity。

這是我的活動代碼：

public class TedActivity extends SherlockFragmentActivity implements 
    TabListener, Constants { 
private Tab tab; 
private ActionBar actionBar; 
private int currentTab; 
MyTedFragment currentFrag; 
private MyTedFragment previousFrag; 
private static int count = 1; 
private static final String TAG = TedActivity.class.getName(); 
private static final String FRAGMENT_PREFIX = "FRAGMENT"; 

@Override 
public void onTabSelected(ActionBar.Tab tab, FragmentTransaction ft) { 
    currentTab = tab.getPosition(); 
    currentFrag = (MyTedFragment) getSupportFragmentManager() 
      .findFragmentByTag(FRAGMENT_PREFIX + (currentTab + 1)); 
    if (previousFrag != null) { 
     ft.hide(previousFrag); 
    } 
    if (currentFrag == null) { 
     Log.d(TAG, FRAGMENT_PREFIX + (currentTab + 1) + " = null"); 
    } else { 
     Log.d(TAG, FRAGMENT_PREFIX + (currentTab + 1) + " != null"); 
     ft.show(currentFrag); 
    } 
    previousFrag = currentFrag; 

} 

/** 
* @see android.app.Activity#onCreate(android.os.Bundle) 
*/ 
@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    actionBar = getSupportActionBar(); 
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS); 
    // Create first Tab 
    FragmentTransaction ft = getSupportFragmentManager().beginTransaction(); 
    MyTedFragment frag = new MyTedFragment(); 
    ft.add(android.R.id.content, frag, FRAGMENT_PREFIX + count); 
    ft.commit(); 
    tab = actionBar.newTab().setTabListener(this); 
    tab.setText("Untitled" + count); 
    actionBar.addTab(tab); 
    count++; 
    if (savedInstanceState != null) { 
     actionBar.setSelectedNavigationItem(savedInstanceState.getInt(
       "tab", 0)); 
    } 
} 


public boolean onCreateOptionsMenu(Menu menu) { 
    addMenuItem(menu, MENU_ID_NEW, R.string.menu_new, 
      R.drawable.ic_action_new).setShowAsAction(
      MenuItem.SHOW_AS_ACTION_ALWAYS); 
    ; 

    return true; 
      addMenuItem(menu, MENU_ID_OPEN, R.string.menu_open, 
      R.drawable.ic_action_open).setShowAsAction(
      MenuItem.SHOW_AS_ACTION_IF_ROOM); 
    ; 
} 

@Override 
protected void onSaveInstanceState(Bundle outState) { 
    super.onSaveInstanceState(outState); 
    outState.putInt("tab", getSupportActionBar() 
      .getSelectedNavigationIndex()); 
} 


@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    currentFrag = (MyTedFragment) getSupportFragmentManager() 
      .findFragmentByTag(FRAGMENT_PREFIX + count); 
    if (currentFrag != null/* && !currentFrag.isDetached() */) { 
     currentFrag.mWarnedShouldQuit = false; 
     switch (item.getItemId()) { 
     case MENU_ID_NEW: 
      FragmentTransaction ft = getSupportFragmentManager() 
        .beginTransaction(); 
      MyTedFragment frag = new MyTedFragment(); 
      ft.add(android.R.id.content, frag, FRAGMENT_PREFIX + count); 
      ft.commit(); 
      tab = actionBar.newTab().setTabListener(this); 
      tab.setText("Untitled" + count); 
      actionBar.addTab(tab); 
      actionBar.setSelectedNavigationItem(actionBar 
        .getNavigationItemCount() - 1); 
      count++; 
      // TODO mFragment.newContent(); 
      return true; 
       case MENU_ID_OPEN: 
      currentFrag.openFile(); 
      break; 

     } 
    } 
    return super.onOptionsItemSelected(item); 
} 

@Override 
public void onTabUnselected(Tab tab, FragmentTransaction ft) { 
    // TODO Auto-generated method stub 
} 

@Override 
public void onTabReselected(Tab tab, FragmentTransaction ft) { 
    // TODO Auto-generated method stub 

} 

}

這裏是我的代碼片段：

public class MyTedFragment extends SherlockFragment implements OnClickListener, KeyListener { 
    private EditText mEditor; 
@Override 
public void onActivityCreated(Bundle savedInstanceState) { 
    // TODO Auto-generated method stub 
    super.onActivityCreated(savedInstanceState); 

    // editor 
    mEditor = (EditText) getActivity().findViewById(R.id.editor); 
    mEditor.addTextChangedListener(this); 
    mEditor.updateFromSettings(); 

} 

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

} 

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

    return inflater.inflate(R.layout.layout_editor, null); 
} 

    .... 
    .... 
    } 

Answer 1

可能是因爲您重新安裝與ft.attach(frag);片段。檢查文檔：http://developer.android.com/reference/android/app/FragmentTransaction.html#attach(android.app.Fragment)