android - 维护 fragment 的 View 状态

Question

我看过Link1对于这个问题，但可以正确理解。我有一个加载列表的 fragment 。当我单击列表项时，它会打开另一个 Activity 。但我按下后退按钮，它再次加载列表。我希望它与之前的滚动位置相同。在上面提到的链接中，它指定使用标志，但我没有明白这一点。

public class MainActivity extends Activity { 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_dashboard); 
    android.app.Fragment fragment = new MeFragment();    
    getFragmentManager().beginTransaction().replace(R.id.layout_FragmentsContainer, fragment).addToBackStack(null).commit();
   }
}

public class MeFragment extends Fragment
{
  @Override
  public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)  
  {
    return inflater.inflate(R.layout.fragment_me, container, false);
  }
  @Override
  public void onActivityCreated(Bundle savedInstanceState) {  
    super.onActivityCreated(savedInstanceState);

    meLV = (ListView) getView().findViewById(R.id.lv_Inbox);
    loadingListProgress = (ProgressBar) getView().findViewById(R.id.progress_LoadingList);  
    meList = new ArrayList<Message>();
    meAdapter = new MessagesListAdapter(getActivity(), meList);  
    //addFooter();
    meLV.setAdapter(meAdapter);
    meLV.setOnItemClickListener(this); 
    pageCount = 0;
    loadmoreProgressDialog = new ProgressDialog(getActivity()); 
    loadmoreProgressDialog.setTitle("Please wait ..."); 
    loadmoreProgressDialog.setMessage("Loading more ...");  
    loadmoreProgressDialog.setCancelable(true);
    loadUserMessages(); 
    meLV.setOnScrollListener(new EndlessScrollListener() {
        @Override
        public void onLoadMore(int page, int totalItemsCount) {
            // TODO Auto-generated method stub
            //addFooter();
            loadmoreProgressDialog.show();
            loadUserMessages();
        }
    }); 
  }  
  @Override
  public void onItemClick(AdapterView<?> parent, View view, int position,
        long id) {
    // TODO Auto-generated method stub
    Utils.showToast_msg(getActivity(), "MessageItemClicked"); 
    ReferralDetailFragment fragment = new ReferralDetailFragment();    
    getFragmentManager().beginTransaction().replace(R.id.layout_FragmentsContainer, fragment).addToBackStack(null).commit();

  }
} 

public class ReferralDetailFragment extends Fragment implements OnClickListener {

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)  
{
    View view = inflater.inflate(R.layout.fragment_referraldetail,container, false);
    linkToAcknowledge   = (TextView) view.findViewById(R.id.lbl_Link_to_Acknowledge);
    return view;  
  }
}

Answer 1

我在我的应用程序中为此实现了一个简单的解决方案，基本上当您再次按下返回 fragment 时，将调用 onCreateView()。在 onCreateView() 中你已经完成了所有的初始化，所以我们改变

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)  
{
    View view = inflater.inflate(R.layout.fragment_me, container, false);
    /*
     *Whatever you want to do
     *
     */
    return view;  
}

到:

View view;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)  
{
    if(view==null){

        view = inflater.inflate(R.layout.fragment_me, container, false);
        /*
         *Whatever you want to do
         *
         */
    }
    else{
         ((ViewGroup)view.getParent()).removeView(view);
    }
    return view;  
}

这里，我们把View View 移到外面，让它成为一个类变量。所以如果是第一次调用fragment，则为null，进行初始化，否则进入else black。 Else block 是必需的，因为 onCreateView() 将它返回的任何内容添加为 View 父级的子级，因此由于 View 已经存在，我们将其删除并 onCreateView 自动再次添加它.