雙片段與動作條

Question

我已經做了一個簡單的Android活動與動作條到2個片段之間切換旋轉的Android。 這一切都確定，直到我旋轉設備。在事實，當我旋轉我有2片段一個比其他：以前的活動之一，第一位的。 爲什麼？ 如果旋轉破壞並重新創建我的活動，我爲什麼得到2個片段？

示例代碼：

活動

package rb.rfrag.namespace; 

import android.app.ActionBar; 
import android.app.ActionBar.Tab; 
import android.app.Activity; 
import android.os.Bundle; 

    public class RFragActivity extends Activity { 
    /** Called when the activity is first created. */ 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     // Notice that setContentView() is not used, because we use the root 
     // android.R.id.content as the container for each fragment 

    // setup action bar for tabs 
     final ActionBar actionBar = getActionBar(); 
     actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS); 
     //actionBar.setDisplayShowTitleEnabled(false); 

     Tab tab; 
     tab = actionBar.newTab() 
       .setText(R.string.VarsTab) 
       .setTabListener(new TabListener<VarValues>(
         this, "VarValues", VarValues.class)); 
     actionBar.addTab(tab); 

     tab = actionBar.newTab() 
       .setText(R.string.SecTab) 
       .setTabListener(new TabListener<SecFrag>(
         this, "SecFrag", SecFrag.class)); 
     actionBar.addTab(tab); 
    } 
} 

TabListener

package rb.rfrag.namespace; 

import android.app.ActionBar; 
import android.app.Activity; 
import android.app.Fragment; 
import android.app.FragmentManager; 
import android.app.FragmentTransaction; 
import android.app.ActionBar.Tab; 

public class TabListener<T extends Fragment> implements ActionBar.TabListener { 
    private Fragment mFragment; 
    private final Activity mActivity; 
    private final String mTag; 
    private final Class<T> mClass; 

    /** Constructor used each time a new tab is created. 
     * @param activity The host Activity, used to instantiate the fragment 
     * @param tag The identifier tag for the fragment 
     * @param clz The fragment's Class, used to instantiate the fragment 
     */ 
    public TabListener(Activity activity, String tag, Class<T> clz) { 
     mActivity = activity; 
     mTag = tag; 
     mClass = clz; 
    } 

    /* The following are each of the ActionBar.TabListener callbacks */ 

    public void onTabSelected(Tab tab, FragmentTransaction ft) {  
     // Check if the fragment is already initialized 
     if (mFragment == null) { 
      // If not, instantiate and add it to the activity 
      mFragment = Fragment.instantiate(mActivity, mClass.getName()); 
      ft.add(android.R.id.content, mFragment, mTag); 
     } else { 
      // If it exists, simply attach it in order to show it 
      ft.attach(mFragment); 
     } 
    } 

    public void onTabUnselected(Tab tab, FragmentTransaction ft) { 
     if (mFragment != null) { 
      // Detach the fragment, because another one is being attached 
      ft.detach(mFragment); 
     } 
    } 
} 

Answer 1

我在活動使用onSaveInstanceState和onRestoreInstanceState保持選定的選項卡和修改解決10如下。

最後修改避免了Android的重建不destoy的片段。不過，我不明白爲什麼活動是由旋轉事件破壞而當前片段沒有。 （你有沒有關於這個設想嗎？）

public void onTabSelected(Tab tab, FragmentTransaction ft) { 
     // previous Fragment management 
     Fragment prevFragment; 
     FragmentManager fm = mActivity.getFragmentManager(); 
     prevFragment = fm.findFragmentByTag(mTag); 
     if (prevFragment != null) { 
      mFragment = prevFragment; 
     } // \previous Fragment management 

     // Check if the fragment is already initialized 
     if (mFragment == null) { 
      // If not, instantiate and add it to the activity 
      mFragment = Fragment.instantiate(mActivity, mClass.getName()); 
      ft.add(android.R.id.content, mFragment, mTag); 
     } else { 
      // If it exists, simply attach it in order to show it 
      ft.attach(mFragment); 
     } 
    } 

Answer 2

由於我使用的是android.support.v4.view.ViewPager覆蓋onTabSelected不會幫助。但你仍然暗示我指出了正確的方向。

android.support.v4.app.FragmentManager將所有片段保存在android.support.v4.app.FragmentActivity的onSaveInstanceState中。 忽略setRetainInstance - 根據您的設計，這可能會導致重複的碎片。

最簡單的解決方法是刪除保存的片段在活動的orCreate：

@Override 
    public void onCreate (final android.os.Bundle savedInstanceState) 
    { 
     if (savedInstanceState != null) 
     { 
     savedInstanceState.remove ("android:support:fragments"); 
     } // if 

     super.onCreate (savedInstanceState); 
… 
     return; 
    } // onCreate 

Answer 3

該解決方案實際上並不需要一大堆的工作，下面的步驟確保，即旋轉屏幕時，選項卡選擇被保留。我遇到了重疊片段，因爲在屏幕旋轉時我的第一個選項卡被選中，而不是在旋轉屏幕之前選擇的第二個選項卡，因此第一個選項卡與第二個選項卡的內容重疊。

這是你的活動應該是什麼樣子（我用ActionBarSherlock但調整應該是很容易的）：

public class TabHostActivity extends SherlockFragmentActivity { 

    private static final String SELETED_TAB_INDEX = "tabIndex"; 


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

    // Setup the action bar 
    ActionBar actionBar = getSupportActionBar(); 
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS); 

    // Create the Tabs you need and add them to the actionBar... 

    if (savedInstanceState != null) { 
     // Select the tab that was selected before orientation change 
     int index = savedInstanceState.getInt(SELETED_TAB_INDEX); 
     actionBar.setSelectedNavigationItem(index); 
    } 
    } 

    @Override 
    protected void onSaveInstanceState(Bundle outState) { 
    super.onSaveInstanceState(outState); 
    // Save the index of the currently selected tab 
    outState.putInt(SELETED_TAB_INDEX, getSupportActionBar().getSelectedTab().getPosition()); 
    } 
} 

而這正是我的ActionBar.TabListener樣子（它在上面的私有類活動）：

private class MyTabsListener<T extends Fragment> implements ActionBar.TabListener { 
    private Fragment fragment; 
    private final SherlockFragmentActivity host; 
    private final Class<Fragment> type; 
    private String tag; 

    public MyTabsListener(SherlockFragmentActivity parent, String tag, Class type) { 
     this.host = parent; 
     this.tag = tag; 
     this.type = type; 
    } 

    @Override 
    public void onTabSelected(Tab tab, FragmentTransaction transaction) { 
     /* 
     * The fragment which has been added to this listener may have been 
     * replaced (can be the case for lists when drilling down), but if the 
     * tag has been retained, we should find the actual fragment that was 
     * showing in this tab before the user switched to another. 
     */ 
     Fragment currentlyShowing = host.getSupportFragmentManager().findFragmentByTag(tag); 

     // Check if the fragment is already initialised 
     if (currentlyShowing == null) { 
      // If not, instantiate and add it to the activity 
      fragment = SherlockFragment.instantiate(host, type.getName()); 
      transaction.add(android.R.id.content, fragment, tag); 
     } else { 
      // If it exists, simply attach it in order to show it 
      transaction.attach(currentlyShowing); 
     } 
    } 

    public void onTabUnselected(Tab tab, FragmentTransaction fragmentTransaction) { 
     /* 
     * The fragment which has been added to this listener may have been 
     * replaced (can be the case for lists when drilling down), but if the 
     * tag has been retained, we should find the actual fragment that's 
     * currently active. 
     */ 
     Fragment currentlyShowing = host.getSupportFragmentManager().findFragmentByTag(tag); 
     if (currentlyShowing != null) { 
      // Detach the fragment, another tab has been selected 
      fragmentTransaction.detach(currentlyShowing); 
     } else if (this.fragment != null) { 
      fragmentTransaction.detach(fragment); 
     } 
    } 

    public void onTabReselected(Tab tab, FragmentTransaction fragmentTransaction) { 
     // This tab is already selected 
    } 

上述實施方式還允許基於其標籤替換選項卡內的片段。爲此，當在同一個選項卡中切換片段時，我使用相同的標籤名稱，用於已添加到選項卡的初始框架。

Answer 4

感謝Martin和asclepix提供他們的解決方案。我有3個選項卡和第一選項卡包含2個片段，像這樣：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 
    android:layout_width="fill_parent" 
    android:layout_height="fill_parent" 
    tools:context=".MainActivity" > 

    <FrameLayout 
     android:id="@+id/frActiveTask" 
     android:layout_width="fill_parent" 
     android:layout_height="50dp" 
     android:layout_alignParentBottom="true" 
     /> 

    <FrameLayout 
     android:id="@+id/frTaskList" 
     android:layout_width="fill_parent" 
     android:layout_height="match_parent" 
     android:layout_alignParentTop="true" 
     android:layout_above="@id/frActiveTask" 
     /> 

</RelativeLayout> 

使用onRestoreInstanceState，onSaveInstanceState和savedInstanceState.remove("android:support:fragments");方法和聲明的工作，除非你主動標籤是不是第一個，幾乎罰款，旋轉和點擊第一，一個清晰的顯示出現，只有第一個標籤上的第二次點擊纔出現右側的片段顯示。 調試代碼後我認識到，第一addTab總是調用中的標籤聽者的onTabSelected事件，具有片段add方法，然後，當setSelectedNavigationItem從onRestoreInstanceState一個detach第一個選項卡上執行稱爲和add爲另一個。 這個不必要的add呼叫在我的解決方案中已修復。

我的活動

protected void onCreate(Bundle savedInstanceState) { 
    boolean firstTabIsNotAdded = false; 
    if (savedInstanceState != null) { 
     savedInstanceState.remove("android:support:fragments"); 
     firstTabIsNotAdded = savedInstanceState.getInt(SELETED_TAB_INDEX) != 0; 
    } 
    super.onCreate(savedInstanceState); 

    setContentView(R.layout.activity_main); 

// codes before adding tabs 

    actionBar = getSupportActionBar(); 
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS); 


    tabStartAndStop = actionBar.newTab().setText(getString(R.string.tab_title_start_and_stop)) 
      .setTabListener(
        new FragmentTabListener<StartStopFragment>(this, 
          getString(R.string.tab_title_start_and_stop_id), 
          StartStopFragment.class, 
          firstTabIsNotAdded)); 
    tabHistory = actionBar.newTab().setText(getString(R.string.tab_title_history)) 
      .setTabListener(
        new FragmentTabListener<HistoryFragment>(this, 
          getString(R.string.tab_title_history_id), 
          HistoryFragment.class, 
          false)); 
    tabRiporting = actionBar.newTab().setText(getString(R.string.tab_title_reporting)) 
      .setTabListener(
        new FragmentTabListener<ReportingFragment>(this, 
          getString(R.string.tab_title_reporting_id), 
          ReportingFragment.class, 
          false)); 

    actionBar.addTab(tabStartAndStop); 

     actionBar.addTab(tabHistory); 
     actionBar.addTab(tabRiporting); 

    } 

    @Override 
    protected void onRestoreInstanceState(Bundle savedInstanceState) { 
     if (savedInstanceState != null) { 
      int index = savedInstanceState.getInt(SELETED_TAB_INDEX); 
      actionBar.setSelectedNavigationItem(index); 
     } 
     super.onRestoreInstanceState(savedInstanceState); 
    } 

    @Override 
    protected void onSaveInstanceState(Bundle outState) { 
     super.onSaveInstanceState(outState); 
     // Save the index of the currently selected tab 
     outState.putInt(SELETED_TAB_INDEX, getSupportActionBar().getSelectedTab().getPosition()); 
    } 

而修改的選項卡監聽器

public class FragmentTabListener<T extends SherlockFragment> implements com.actionbarsherlock.app.ActionBar.TabListener { 
    private Fragment mFragment; 
    private final Activity mFragmentActivity; 
    private final String mTag; 
    private final Class<T> mClass; 
    private boolean doNotAdd; 

    /** Constructor used each time a new tab is created. 
     * @param activity The host Activity, used to instantiate the fragment 
     * @param tag The identifier tag for the fragment 
     * @param clz The fragment's Class, used to instantiate the fragment 
     */ 
    public FragmentTabListener(Activity activity, String tag, Class<T> clz, boolean doNotAdd) { 
     mFragmentActivity = activity; 
     mTag = tag; 
     mClass = clz; 
     this.doNotAdd = doNotAdd; 
    } 

    /* The following are each of the ActionBar.TabListener callbacks */ 
    public void onTabSelected(Tab tab, FragmentTransaction ft) { 

     // Check if the fragment is already initialized 
     if (mFragment == null) { 
      // If not, instantiate and add it to the activity 
      if(doNotAdd){ 
       doNotAdd = false; 
      }else{ 
       mFragment = Fragment.instantiate(mFragmentActivity, mClass.getName()); 
       ft.add(android.R.id.content, mFragment, mTag); 
      } 
     } else { 
      // If it exists, simply attach it in order to show it 
      ft.attach(mFragment); 
     } 
    } 

    public void onTabUnselected(Tab tab, FragmentTransaction ft) { 
     if (mFragment != null) { 
      // Detach the fragment, because another one is being attached 
      ft.detach(mFragment); 
     } 
    } 

    public void onTabReselected(Tab tab, FragmentTransaction ft) { 
     // User selected the already selected tab. Usually do nothing. 
    } 
}