在方向改变时处理 Fragment 的万无一失的方法 [英] Fool-proof way to handle Fragment on orientation change

问题描述

public class MainActivity extends Activity implements MainMenuFragment.OnMainMenuItemSelectedListener {

 @Override
 public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    FragmentManager fragmentManager = getFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager
            .beginTransaction();

    // add menu fragment
    MainMenuFragment myFragment = new MainMenuFragment();
    fragmentTransaction.add(R.id.menu_fragment, myFragment);

    //add content
    DetailPart1 content1= new DetailPart1 ();
    fragmentTransaction.add(R.id.content_fragment, content1);
    fragmentTransaction.commit();

}
public void onMainMenuSelected(String tag) {
  //next menu is selected replace existing fragment
}

我需要并排显示两个列表视图，左侧的菜单和右侧的内容.默认情况下，第一个菜单被选中，其内容显示在右侧.显示内容的Fragment如下:

I have a need to display two list views side by side, menu on left and its content on right side. By default, the first menu is selected and its content is displayed on right side. The Fragment that displays content is as below:

public class DetailPart1 extends Fragment {
  ArrayList<HashMap<String, String>> myList = new ArrayList<HashMap<String, String>>();
  ListAdapter adap;
  ListView listview;

  @Override
  public void onActivityCreated(Bundle savedInstanceState) {
      super.onActivityCreated(savedInstanceState);

       if(savedInstanceState!=null){
        myList = (ArrayList)savedInstanceState.getSerializable("MYLIST_obj");
        adap = new LoadImageFromArrayListAdapter(getActivity(),myList );
        listview.setAdapter(adap);
       }else{
        //get list and load in list view
        getlistTask = new GetALLListTasks().execute();
    }


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


     @Override
      public void onSaveInstanceState(Bundle outState) {
         super.onSaveInstanceState(outState);
          outState.putSerializable("MYLIST_obj", myList );
        }
    }

onActivityCreated 和 onCreateView 被调用两次.有很多使用片段的例子.由于我是这个主题的初学者，我无法将示例与我的问题联系起来.我需要一种万无一失的方法来处理方向变化.我没有在清单文件中声明 android:configChanges.我需要活动销毁和重新创建，以便我可以在横向模式下使用不同的布局.

The onActivityCreated and onCreateView are called twice. There are many examples out there using fragments. Since I am beginner in this subject, I am unable relate the example with my problem. I need a fool proof way to handle orientation change. I have NOT declared android:configChanges in manifest file. I need the activity destroy and recreate so that I can use different layout in landscape mode.

推荐答案

你在你的 Activity 中每次转动屏幕时都在创建一个新的片段 onCreate(); 但是你也在维护旧的带有 super.onCreate(savedInstanceState); 的.所以也许可以设置标签并找到存在的片段，或者将空包传递给超级.

You are creating a new fragment every time you turn the screen in your activity onCreate(); But you are also maintaining the old ones with super.onCreate(savedInstanceState);. So maybe set tag and find the fragment if it exists, or pass null bundle to super.

这花了我一段时间来学习，当你使用 viewpager 之类的东西时真的很痛苦.

This took me a while to learn and it can really be a pain when you are working with stuff like viewpager.

我建议您多花些时间阅读fragments涵盖了这个确切的主题.

I'd recommend you to read about fragments an extra time as this exact topic is covered.

以下是如何在常规方向更改时处理片段的示例:

Here is an example of how to handle fragments on a regular orientation change:

活动:

public class MainActivity extends FragmentActivity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        if (savedInstanceState == null) {
            TestFragment test = new TestFragment();
            test.setArguments(getIntent().getExtras());
            getSupportFragmentManager().beginTransaction().replace(android.R.id.content, test, "your_fragment_tag").commit();
        } else {
            TestFragment test = (TestFragment) getSupportFragmentManager().findFragmentByTag("your_fragment_tag");
        }
    }
}

片段:

public class TestFragment extends Fragment {

    public static final String KEY_ITEM = "unique_key";
    public static final String KEY_INDEX = "index_key";
    private String mTime;
    
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_layout, container, false);
        
        if (savedInstanceState != null) {
            // Restore last state
            mTime = savedInstanceState.getString("time_key");
        } else {
            mTime = "" + Calendar.getInstance().getTimeInMillis();
        }
        
        TextView title = (TextView) view.findViewById(R.id.fragment_test);
        title.setText(mTime);
        
        return view;
    }
    
    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putString("time_key", mTime);
    }
}

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