我不止一次看到这个问题在这里被问到，但我不知道如何解决我的问题。

我有一个用户执行此操作的应用:

1 - 打开 navigationDrawer 并选择一个选项(创建了一个 fragment )(我在这里选择第二个选项)；

public void selectItem(int position) {
        Fragment fragment = null;
        switch (position) {
            case FRAGMENT_OPTION1:
                ...
                break;
            case FRAGMENT_OPTION2:
                fragment = ControlPanelFragment.newInstance();
                break;
            ...
            case FRAGMENT_OPTIONN:
                ...
                return;
            default:
                break;
        }
        if (fragment != null) {
            FragmentManager fragmentManager = getSupportFragmentManager();
            fragmentManager.beginTransaction().replace(R.id.fragment_container, fragment).commitAllowingStateLoss();
        }
}

2 - 加载选定的选项 (ControlPanelFragment): 2.1 - 控制面板有选项卡和 iconpager。对于每个寻呼机页面和每个选项卡，都会创建一个新 fragment 。我有 3 个选项卡和 3 个页面，因此创建了 9 个 fragment ；

@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    if (savedInstanceState != null) {
        currentControlPanelOption = savedInstanceState.getInt("currentControlPanelOption", currentControlPanelOption);
        currentControlPanelTab = savedInstanceState.getInt("currentControlPanelTab", currentControlPanelTab);
    }
    setControlPanelTabs();
    setIconPager();
}

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putInt("currentControlPanelOption", pager.getCurrentItem());
    outState.putInt("currentControlPanelTab", mTabHost.getCurrentTab());
}

3 - 在 setIconPager(); 我有这段代码:

pager = (ViewPager) view.findViewById(R.id.pager);
cPanelPagerAdapter = new ControlPanelPagerAdapter(getChildFragmentManager());
pager.setOffscreenPageLimit(2);
pager.setAdapter(cPanelPagerAdapter);

ControlPanelPagerAdapter 有这段代码:

public Fragment getItem(int index) {
    Fragment fragment;
    switch (index) {
        case 1:
            fragment = FragmentA.newInstance();
            break;
        case 2:
            fragment = FragmentB.newInstance();
            break;
        case 3:
            fragment = FragmentC.newInstance();
            break;
        default:
            fragment = null;
            break;
    }
    ...
    return fragment;
}

4 - FragmentA、FragmentB 和FragmentC 的代码几乎相同:

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

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    if (savedInstanceState == null) {
        fragmentA_Data = new FragmentADetail[3];
        createTabInstance(0);
    } else {
        fragmentA_Data = (FragmentADetail[]) savedInstanceState.getSerializable("Data");
        return;
    }
}
private void createTabInstance(int tab) {
    new FragmentADetail();
    fragment = FragmentADetail.newInstance(tab);

    Bundle args = new Bundle();
    args.putInt("tab", tab);
    fragment.setArguments(args);

    fragmentA_Data[tab] = fragment;
    FragmentTransaction fragmentTransaction = getChildFragmentManager().beginTransaction();
    fragmentTransaction.replace(R.id.fragment_placeholder, fragmentA_Data[tab]);
    fragmentTransaction.commitAllowingStateLoss();
}
public void getTabData(int tab) {
    if (fragmentA_Data[tab] == null) {
        createStoreTimePeriodInstance(tab);
    } else {
        if (fragmentA_Data[tab].getArguments() == null) {
            Bundle args = new Bundle();
            args.putInt("tab", tab);
            fragmentA_Data[tab].setArguments(args);
        }
        FragmentTransaction fragmentTransaction = getChildFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.fragment_placeholder, fragmentA_Data[tab]);
        fragmentTransaction.commitAllowingStateLoss();
    }
}
@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putSerializable("data", fragmentA_Data);
}

5 - 最后，FragmentADetail 有这段代码:

public static FragmentADetail newInstance(int tab) {
    selectedTab = tab;
    return new FragmentADetail();
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    view = inflater.inflate(R.layout.details_fragment, container, false);
    ...
    if (savedInstanceState != null) {
        selectedTab = savedInstanceState.getInt("selectedTab");
    }
    ...
}

public void getTabData(int tab) {
    //This is where I'm getting the data that populates the layout
}

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

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    Bundle args = getArguments();
    if (args != null) {
       getTabData(args.getInt("tab"));
    }
}

现在，假设我在 FragmentA 上并选择了第三个选项卡。如果我旋转屏幕，我会得到以下事件序列:

1. ControlPanelFragment onSaveInstanceState 保存当前选项卡和当前 fragment
2. FragmentA onSaveInstanceState 为寻呼机保存选项卡 fragment
3. navigationDrawer 第二个选项再次调用 fragment = ControlPanelFragment.newInstance();
4. ControlPanelFragment onViewCreated 被调用，我可以获得保存的数据信息并创建一个新的分页器和标签
5. FragmentA onViewCreated 被调用，我可以提取保存的数据
6. FragmentADetail onActivityCreated 获取保存的数据并正确加载数据(至少我认为) 从现在开始，第二组方法被第二次调用，之前保存的数据被重置，所以现在显示错误的数据
7. ControlPanelFragment onSaveInstanceState 但现在 savedInstanceState 为空
8. ControlPanelPagerAdapter getItem 调用实例化 3 个 fragment
9. FragmentA onSaveInstanceState 现在已调用但 savedInstanceState 为空
10. FragmentADetail onActivityCreated 已调用，但现在选项卡 = 0

谁能解释一下我怎样才能阻止第 7 步到第 10 步的发生？

最佳答案

我弄清楚我的问题是什么。

当我在做的时候:

case FRAGMENT_OPTION2:
    fragment = ControlPanelFragment.newInstance();
break;

我正在创建一个 fragment ，当我旋转屏幕时 selectItem(int position) 再次被调用，因此创建了同一对象的新实例因此步骤 7和以下。解决方案是检查 fragment 是否已经创建并使用他而不是创建新 fragment 。 我保存了带有标签的初始 fragment ，他们正在寻找该标签。如果标签存在，则使用该 fragment ，否则创建一个新 fragment 。

public void selectItem(int position) {
        Fragment fragment = null;
        switch (position) {
            case FRAGMENT_OPTION1:
                ...
                break;
            case FRAGMENT_OPTION2:
                fragment = getSupportFragmentManager().findFragmentByTag(String.valueOf(position));
                if (fragment == null) {
                    fragment = ControlPanelFragment.newInstance();
                }
                break;
            ...
            case FRAGMENT_OPTIONN:
                ...
                return;
            default:
                break;
        }
        if (fragment != null) {
            FragmentManager fragmentManager = getSupportFragmentManager();
            fragmentManager.beginTransaction().replace(R.id.fragment_container, fragment, 
                    String.valueOf(position)).commitAllowingStateLoss();
        }
}

关于Android oncreateview 调用了两次，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/27723968/