setCurrentItem嵌套viewpager

Question

我有嵌套在一個片段ViewPager，當設備改變方向，我想保存和恢復ViewPager是在哪一頁。目前，我正在這樣做：

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
    mViewPager = (ViewPager) inflater.inflate(R.layout.activity_albumpicker, container, false); 

    // Create the adapter that will return a fragment for each of the three 
    // primary sections of the activity. 
    mSectionsPagerAdapter = new SectionsPagerAdapter(getChildFragmentManager()); 

    setRetainInstance(true); 

    // Set up the ViewPager with the sections adapter. 
    mViewPager.setAdapter(mSectionsPagerAdapter); 

    if(savedInstanceState != null) { 
     mViewPager.setCurrentItem(savedInstanceState.getInt("pagerState"), false); 
    } 
    return mViewPager; 
} 

@Override 
public void onSaveInstanceState(Bundle outState) { 
    super.onSaveInstanceState(outState); 
    outState.putInt("pagerState", mViewPager.getCurrentItem()); 
} 

期間onSaveInstanceState值被保存是正確的，在onCreateView旋轉savedInstanceState.getInt("pagerState")值後也是正確的。但沒有任何反應，ViewPager停留在它的默認頁面上，logcat中沒有任何內容。我很難過。

Answer 1

經過幾個小時的審查一些特定的東西，我想出了以下解決方案（這是一種通常的做法，我想）。我包括您已完成的兩個步驟以及其他必要步驟。

• 1. 呼叫setRetainInstance(true);（你這樣做）
• 設置片段的節能狀態。 （你已經這樣做了）
• 在主機活動，請撥打以下，以確保您的片段已經保存在活動的狀態：

Here is a snippet:

... (other stuffs) 

Fragment mainFragment; // define a local member 

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

    // After you rotate your screen, by default your Activity will be recreated  
    // with a bundle of saved states, i.e at this point, savedInstanceState is  
    // not null in general. If you debug it, you could see how it saved your 
    // latest FragmentTransactionState, which hold your Fragment's instance 

    // For safety, we check it here, and retrieve the fragment instance. 
    mainFragment = getSupportFragmentManager().findFragmentById(android.R.id.content); 
    if (mainFragment == null) { 

    // in very first creation, your fragment is null obviously, so we need to 
    // create it and add it to the transaction. But after the rotation, its 
    // instance is nicely saved by host Activity, so you don't need to do 
    // anything. 

    mainFragment = new MainFragment(); 
    getSupportFragmentManager().beginTransaction() 
     .replace(android.R.id.content, mainFragment) 
     .commit(); 
    } 
} 

這就是我做的，使它的工作原理。希望這可以幫助。