避免在片段旋轉過程中耗時加載數據

Question

我想避免在Fragment旋轉過程中耗時的數據加載。

public class WatchlistFragment extends SherlockListFragment { 
    @Override 
    public void onActivityCreated(Bundle savedInstanceState) { 
     super.onActivityCreated(savedInstanceState); 

     if (savedInstanceState == null) { 
      data = getTimeConsumingData();   
     } else { 
      Log.i(TAG, "savedInstanceState is not null!"); 
      // Avoid performing time consuming data operation during rotation changes. 
      // But I never have chance to reach here !?!? 
      data = savedInstanceState.getStringArray("data"); 
     } 
     setListAdapter(new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, data)); 
    } 

    public String[] getTimeConsumingData() { 
     Log.i(TAG, "WatchlistFragment getTimeConsumingData"); 
     return new String[] { "A", "B", "C"}; 
    } 

    @Override 
    public void onSaveInstanceState(Bundle outState) { 
     Log.i(TAG, "WatchlistFragment onSaveInstanceState"); 
     super.onSaveInstanceState(outState); 
     outState.putStringArray("data", data); 
    } 

    private String[] data = null; 
    private static final String TAG = WatchlistFragment.class.getSimpleName(); 
} 

奇怪的是，在savedInstanceState是onActivityCreated總是空連我執行幾個旋轉。

請注意，我不喜歡使用setRetainInstance(true)描述Android Fragments Retaining Data作者正在使用onSaveInstanceState。只是我不知道爲什麼我的不工作。

Answer 1

另一種方法是使用新的，超級聰明，裝載模式，可以很容易地實現並讓系統爲您處理所有這些問題：

http://developer.android.com/guide/components/loaders.html

Answer 2

只是在你的片段使用setRetainInstance(true)和檢查savedInstanceState==null和不覆蓋onSaveInstanceState

UPDATE

private ArrayAdapter<String> adapter = null; 
public void onActivityCreated(Bundle savedInstanceState) { 
    super.onActivityCreated(savedInstanceState); 
    setReatainInstance(true); 
    if(adapter==null){ 
     adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1,getTimeConsumingData()); 
    } 
    setListAdapter(adapter); 
} 

Answer 3

如果您使用的是加載器，請在加載數據後使用loadermanager.destory（loader_id）。它將不會再次加載配置更改。