无法保存片段的实例屏幕旋转后不重新启动

Question

我的片段的代码如下所示：

public class AllIssuesFragment extends Fragment { 

@Bind(R.id.list_all_issues) ListView mListAllIssues; 
IssuesGetter ai; 
ArrayAdapter<IssuesResponse.Issue> adapter; 

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
         Bundle savedInstanceState) { 
    View view = inflater.inflate(R.layout.fragment_all_issues, container, false); 
    return view; 
} 

@Override 
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) { 
    super.onViewCreated(view, savedInstanceState); 
    ButterKnife.bind(this, view); 
    setRetainInstance(true); 

    SharedPreferences user_data = this.getActivity().getSharedPreferences("user_data", Context.MODE_PRIVATE); 
    UserManager.getInstance().setUsername(user_data.getString("username", null)); 
    UserManager.getInstance().setPassword(user_data.getString("password", null)); 

    if(UserManager.getInstance().getUsername() == null || UserManager.getInstance().getPassword() == null) { 
     Intent intent = new Intent(getActivity(), ChangeUserActivity.class); 
     startActivity(intent); 
    } 
    else { 
     adapter = new ArrayAdapter<>(getActivity(), android.R.layout.simple_list_item_1); 
     if(savedInstanceState == null) { 
      getIssues(Constants.URI + Constants.ISSUES + Constants.OFFSET + 0); 
     } 
     mListAllIssues.setOnScrollListener(new AbsListView.OnScrollListener() { 
      @Override 
      public void onScrollStateChanged(AbsListView absListView, int i) { 

      } 

      @Override 
      public void onScroll(AbsListView absListView, int firstVisible, int visibleCount, int totalCount) { 
       boolean loadMore = firstVisible + visibleCount >= totalCount; 

       if (loadMore && ai.getStatus() == AsyncTask.Status.FINISHED) { 
        getIssues(Constants.URI + Constants.ISSUES + Constants.OFFSET + totalCount); 
        mListAllIssues.setSelection(totalCount); 
       } 
      } 
     }); 
    } 
} 

private void getIssues(String url) { 
    ai = new IssuesGetter(new AsyncCallback<IssuesResponse>() { 
     @Override 
     public void onSuccess(IssuesResponse response) { 
      int index = mListAllIssues.getFirstVisiblePosition(); 
      View v = mListAllIssues.getChildAt(0); 
      int top = (v == null)? 0 : v.getTop(); 

      adapter.addAll(response.getIssues()); 
      adapter.notifyDataSetChanged(); 
      mListAllIssues.setAdapter(adapter); 
      mListAllIssues.setSelectionFromTop(index, top); 
     } 

     @Override 
     public void onError() { 
      Intent intent = new Intent(getActivity(), ChangeUserActivity.class); 
      startActivity(intent); 
     } 
    }); 
    ai.execute(url); 
} 
} 

MainActivity.java：

public class MainActivity extends AppCompatActivity { 


@Bind(R.id.viewpager) ViewPager viewPager; 
@Bind(R.id.tabs) PagerSlidingTabStrip tabStrip; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    ButterKnife.bind(this); 
    viewPager.setAdapter(new MainActivityPagerAdapter(getSupportFragmentManager())); 
    tabStrip.setViewPager(viewPager); 
} 

@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.menu_main, menu); 
    return true; 
} 

@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    // Handle action bar item clicks here. The action bar will 
    // automatically handle clicks on the Home/Up button, so long 
    // as you specify a parent activity in AndroidManifest.xml. 
    int id = item.getItemId(); 

    //noinspection SimplifiableIfStatement 
    if (id == R.id.action_change_user) { 
     Intent intent = new Intent(this, ChangeUserActivity.class); 
     this.startActivity(intent); 
     return true; 
    } 

    return super.onOptionsItemSelected(item); 
} 
} 

我试着使用setRetainInstance（true）并检查savedInstanceState是否为空，但它没有解决我的问题EM。我坚持:(

我的AsyncTask返回结果使用回拨

Answer 1

我看到这里的问题：。

public void onCreate() { 
    //.. 
    viewPager.setAdapter(new MainActivityPagerAdapter(getSupportFragmentManager())); 
    tabStrip.setViewPager(viewPager); 
} 

这种方法被称为每次活动重新创建它的作用是产生这是一个问题，因为你的活动不控制片段的创建，这是保留片段所必需的。

我建议你在onSaveInstanceState（）中保存片段的状态，回调和在onCreateView（）中恢复它。请注意，您不需要保存UI元素的状态只是片段类的变量。如果UI元素具有唯一的ID，则会自动保存其状态。

编辑：

我的建议：

public class AllIssuesFragment extends Fragment { 
    private List<String> issues; 
    // .. 

    @Nullable 
    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
     // .. 
     if (null != savedInstanceState) { 
      issues = savedInstanceState.getStringArray("issues"); 
     } else { 
      issues = new List<>(); 
     } 
     adapter = new ArrayAdapter<>(getActivity(), android.R.layout.simple_list_item_1, issues); 
     // .. 
    } 

    @Override 
    public void onSaveInstanceState(Bundle outState) { 
     super.onSaveInstanceState(outState); 
     outState.putStringArray("issues", issues); 
    } 

    private void getIssues(String url) { 
     // .. 
     ai = new IssuesGetter(new AsyncCallback<IssuesResponse>() { 
      @Override 
      public void onSuccess(IssuesResponse response) { 
       // .. 
       //adapter.addAll(response.getIssues()); 
       issues.addAll(response.getIssues()); 
       adapter.notifyDataSetChanged(); 
       // .. 
      } 
     }; 
     // .. 
    } 
}