ViewPager 中的一个片段不显示

Question

我有一个托管 viewpager 的选项卡式活动（使用 eclipse 向导自动生成）。我只是稍微修改了自动生成的 FragmentPagerAdapter 以便在每个选项卡上实例化一个特定的片段。最初我有 4 个选项卡，第一个选项卡有 3 个片段，最后一个选项卡仍然是自动生成的占位符，它们起作用了。当我用我的片段之一的实例替换最后一个占位符时，我遇到了以下问题：最后两个选项卡之一中的片段保持空白，如下所示：

_____第一个TAB___|____第二个TAB_|___第3个TAB_____|____第4个TAB____|

[MasterFragment][RequestMap][MasterFragment][MasterFragment]

这保持空白_____________________|

此外，如果我进行“随机”操作序列（更改选项卡，单击按钮以执行某些操作，...），则未显示的片段交换，并成为最后一个，如下所示：

_____第一个TAB___|____第二个TAB_|___第3个TAB_____|____第4个TAB____|

[MasterFragment][RequestMap][MasterFragment][MasterFragment]

这保持空白__________________________________|

这是我的 FragmentPagerAdapter 的代码：

public class SectionsPagerAdapter extends FragmentPagerAdapter {

    public SectionsPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        switch (position) {
        case REQUEST_TAB:
            masterFragment = new MasterFragment(MasterFragment.ALL_REQUEST);
            return masterFragment;
        case MAP_TAB:
            requestMap = new RequestMap();
            return requestMap;
        case OWNER_TAB:
            masterFragmentOwner = new MasterFragment(MasterFragment.OWNER_REQUEST);
            System.out.println("I should have created the Owner MasterFragment");
            return masterFragmentOwner;
        case JOINED_TAB:
            masterFragmentJoined = new MasterFragment(MasterFragment.JOINED_REQUEST);
            return masterFragmentJoined;
        }
        return null;
    }

    @Override
    public int getCount() {
        return 4;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        Locale l = Locale.getDefault();
        switch (position) {
        case REQUEST_TAB:
            return getString(R.string.request_tab_title).toUpperCase(l);
        case MAP_TAB:
            return getString(R.string.map_tab_title).toUpperCase(l);
        case OWNER_TAB:
            return getString(R.string.owner_tab_title).toUpperCase(l);
        case JOINED_TAB:
            return getString(R.string.joined_tab_title).toUpperCase(l);
        default:
            return "";
        }
    }
}

我省略了有关 viewPager 设置的代码，因为它与 eclipse 向导自动生成的代码相同。虽然这里是 MasterFragment 类的代码：

package it.polimi.frontend.fragment;

import it.polimi.appengine.entity.manager.model.Request;
import it.polimi.appengine.entity.manager.model.User;
import it.polimi.frontend.activity.R;
import it.polimi.frontend.util.QueryManager;
import it.polimi.frontend.util.QueryManager.OnRequestLoadedListener;

import java.util.ArrayList;
import java.util.List;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.view.InflateException;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class MasterFragment extends Fragment implements OnRequestLoadedListener, RequestList.OnRequestSelectedListener, RequestDetail.OnUserClickedListener{

private boolean twoPane;
private static View view;
public final static int ALL_REQUEST=0;
public final static int OWNER_REQUEST=1;
public final static int JOINED_REQUEST=2;
private int mode;

public MasterFragment(){
    this.mode=0;
}
public MasterFragment(int mode){
    this.mode=mode;
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    QueryManager.getInstance().addListener(this);
    if (view != null) {
        ViewGroup parent = (ViewGroup) view.getParent();
        if (parent != null)
            parent.removeView(view);
    }
    try {
        view = inflater.inflate(R.layout.fragment_master,container, false);
        List<Request> requests = new ArrayList<Request>();
        RequestList requestListFragment = null;
        switch (mode) {
        case OWNER_REQUEST:
            requests = QueryManager.getInstance().getCurrentUser().getRequests();
            System.out.println("Dovrei aver recuperato le richieste dell'owner");
            break;
        case JOINED_REQUEST:
            String mail=null;
            if (QueryManager.getInstance().getCurrentUser()!=null){
                User current =QueryManager.getInstance().getCurrentUser();
                mail = current.getPwAccount() != null ? 
                        current.getPwAccount()
                        : current.getGmailAccount() != null ?
                                current.getGmailAccount() 
                                : current.getFbAccount() != null ?
                                        current.getFbAccount()
                                        : null;
                requests = QueryManager.getInstance().getUserPartecipation(mail);
            }
            else
                requests = new ArrayList<Request>();
            break;
        default: //ALL_REQUEST case and all the other possibilities
            requests = QueryManager.getInstance().getRequests();
            break;
        }
        requestListFragment = new RequestList(requests, mode);
        if (view.findViewById(R.id.detail_container) != null) {//TABLET CASE
            twoPane = true;
            getChildFragmentManager().beginTransaction()
            .replace(R.id.request_list_container,requestListFragment,RequestList.ID)
            .commit();

        } else { //PHONE CASE:
            getChildFragmentManager().beginTransaction()
            .replace(R.id.container,requestListFragment,RequestList.ID)
            .commit();
        }
    } catch (InflateException e) {
        // is already there, just return view as it is
        e.printStackTrace();
    }
    return view;
}

@Override
public void onRequestSelected(int position, Request request) {
    if (twoPane) {
        DetailContainerFragment detailContFrag = new DetailContainerFragment(request,mode);
        getChildFragmentManager().beginTransaction()
        .replace(R.id.detail_container, detailContFrag, DetailContainerFragment.ID).commit();
    } else {
        switch (mode) {//This empty switch if for future changes
        case OWNER_REQUEST:
            break;
        case JOINED_REQUEST:
            break;
        default://ALL_REQUEST               
            break;
        }
        RequestDetail fragment = new RequestDetail(request,mode);
        Fragment reqList=getChildFragmentManager().findFragmentByTag(RequestList.ID);

        getChildFragmentManager().beginTransaction()
        .hide(reqList)
        .addToBackStack(RequestDetail.ID)
        .add(R.id.container,fragment,RequestDetail.ID)
        .commit();
    }
}

@Override
public void onUserClicked(User user,String requestId) {
    if (!twoPane) {
        FeedbackDetail fragment = new FeedbackDetail(user,this.mode,requestId);
        Fragment reqDetail=getChildFragmentManager().findFragmentByTag(RequestDetail.ID);

        getChildFragmentManager().beginTransaction()
        .hide(reqDetail)
        .addToBackStack(FeedbackDetail.ID)
        .add(R.id.container,fragment,FeedbackDetail.ID)
        .commit();

    } else {
        /*DetailContainerFragment should take care of it*/
    }
}
@Override
public void onRequestLoaded(List<Request> requests) {
    System.out.println("Ho caricato: "+requests.size());
    RequestList requestListFragment = (RequestList)getChildFragmentManager().findFragmentByTag(RequestList.ID);
    switch (mode) {//Also this switch is for future changes, but the requests list is anyway fetched and assigned to RequestList above
    case OWNER_REQUEST:
        //TODO
        break;
    case JOINED_REQUEST:
        //TODO
        break;
    default: //ALL_REQUEST
        if (requestListFragment!=null)
            requestListFragment.setRequestAdapter(requests);
        break;
    }
}

}

如果我遗漏了一些重要的东西，请告诉我。 先谢谢大家了

编辑： 我忘了说我放置的 System.out 显示在控制台中，所以应该已经创建了“空白”片段，并且应该通过他的 onCreateView()。

Answer 1

我发现了错误。问题是

private static View view;

因为静态属性。删除“静态”它再次起作用。实际上，即使现在我也无法解释它是如何在第一个和最后一个选项卡上工作一段时间而不是在第三个选项卡上工作的，因为静态属性应该在类的所有实例之间共享。由于 ViewPager 的内部结构，问题似乎只出现在相邻的相同 MasterFragment 上，如果它们与它工作的任何其他片段交错。