在ViewPager中管理子片段会导致IllegalStateException

Question

我的应用有一个SlidingMenu，菜单中的每个项目都是一个新的SherlockFragment。大多数是简单的单窗格片段，但我遇到的问题应该是双窗格。我决定使用带有ActionBar Tabs的ViewPager来实现它。

ViewPager有两个页面，CustomerFragment（客户列表）和CartFragment（购物车项目网格，顶部有TextView，用于显示所选客户的名称）。当用户单击某人的姓名时，ViewPager将翻页并显示该名称。由于它全部包含在父片段中，因此我决定使用ChildFragmentManager实现ViewPager的最佳方法是：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    mViewPager = new ViewPager(activity);
    mViewPager.setId(1);
    v = mViewPager;
    fm = getChildFragmentManager();

    custFrag = CashRegisterCustomerFragment.newInstance();
    cartFrag = CashRegisterCartFragment.newInstance();

    fm.beginTransaction().add(mViewPager.getId(), custFrag).commitAllowingStateLoss();
    fm.beginTransaction().add(mViewPager.getId(), cartFrag).commitAllowingStateLoss();

    mActionBar = activity.getSupportActionBar();
    mActionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    mTabsAdapter = new CashRegisterTabsAdapter(activity, mViewPager);
    mTabsAdapter.addTab(mActionBar.newTab().setText(activity.getResources().getString(R.string.customer_list)), 
        custFrag);
    mTabsAdapter.addTab(mActionBar.newTab().setText(activity.getResources().getString(R.string.items)), 
        cartFrag);

    if (savedInstanceState != null) {
        mActionBar.setSelectedNavigationItem(savedInstanceState.getInt("tab", 0));
    } else {
        mActionBar.setSelectedNavigationItem(0);
    }

    return v;
}

CashRegisterTabsAdapter的重要部分：

public CashRegisterTabsAdapter(MyActivity act, ViewPager pager) {
    super(act.getSupportFragmentManager());
    activity = act;
    mActionBar = activity.getSupportActionBar();
    mActionBar.setTitle(R.string.cash_register);
    mViewPager = pager;
    mViewPager.setAdapter(this);
    mViewPager.setOnPageChangeListener(this);
}

public void addTab(ActionBar.Tab tab, BaseFragment frag) {
    tab.setTabListener(this);
    mTabs.add(frag);
    mActionBar.addTab(tab);
    notifyDataSetChanged();
}

@Override
public int getCount() {
    return mTabs.size();
}

@Override
public Fragment getItem(int position) {
    return mTabs.get(position);
}

@Override
public void onPageSelected(int position) {
    mActionBar.setSelectedNavigationItem(position);

    if (position == 1)
        activity.getSlidingMenu().setSlidingEnabled(false);
    else
        activity.getSlidingMenu().setSlidingEnabled(true);
}

@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {        
    int pos = tab.getPosition();
    if (mViewPager != null) {
        mViewPager.setCurrentItem(pos);
    }
}

一切都很好。但是，当我通过SlidingMenu切换片段然后点击主页按钮，将应用程序发送到后台时，我遇到了这个：

07-02 18:04:31.170: E/AndroidRuntime(32619): FATAL EXCEPTION: main
07-02 18:04:31.170: E/AndroidRuntime(32619): java.lang.IllegalStateException: Failure saving state: active CashRegisterCustomerFragment{41a8f1a0} has cleared index: -1
07-02 18:04:31.170: E/AndroidRuntime(32619):    at android.support.v4.app.FragmentManagerImpl.saveAllState(FragmentManager.java:1700)
07-02 18:04:31.170: E/AndroidRuntime(32619):    at android.support.v4.app.FragmentActivity.onSaveInstanceState(FragmentActivity.java:527)
07-02 18:04:31.170: E/AndroidRuntime(32619):    at com.actionbarsherlock.app.SherlockFragmentActivity.onSaveInstanceState(SherlockFragmentActivity.java:127)
07-02 18:04:31.170: E/AndroidRuntime(32619):    at com.jeremyfeinstein.slidingmenu.lib.app.SlidingFragmentActivity.onSaveInstanceState(SlidingFragmentActivity.java:50)
07-02 18:04:31.170: E/AndroidRuntime(32619):    at com.mycom.myapp.MyActivity.onSaveInstanceState(MyActivity.java:128)
07-02 18:04:31.170: E/AndroidRuntime(32619):    at com.mycom.myapp.MainFragmentContainer.onSaveInstanceState(MainFragmentContainer.java:124)
07-02 18:04:31.170: E/AndroidRuntime(32619):    at android.app.Activity.performSaveInstanceState(Activity.java:1137)
07-02 18:04:31.170: E/AndroidRuntime(32619):    at android.app.Instrumentation.callActivityOnSaveInstanceState(Instrumentation.java:1215)
07-02 18:04:31.170: E/AndroidRuntime(32619):    at android.app.ActivityThread.performStopActivityInner(ActivityThread.java:3077)
07-02 18:04:31.170: E/AndroidRuntime(32619):    at android.app.ActivityThread.handleStopActivity(ActivityThread.java:3136)
07-02 18:04:31.170: E/AndroidRuntime(32619):    at android.app.ActivityThread.access$900(ActivityThread.java:142)
07-02 18:04:31.170: E/AndroidRuntime(32619):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1235)
07-02 18:04:31.170: E/AndroidRuntime(32619):    at android.os.Handler.dispatchMessage(Handler.java:99)
07-02 18:04:31.170: E/AndroidRuntime(32619):    at android.os.Looper.loop(Looper.java:137)
07-02 18:04:31.170: E/AndroidRuntime(32619):    at android.app.ActivityThread.main(ActivityThread.java:4931)
07-02 18:04:31.170: E/AndroidRuntime(32619):    at java.lang.reflect.Method.invokeNative(Native Method)
07-02 18:04:31.170: E/AndroidRuntime(32619):    at java.lang.reflect.Method.invoke(Method.java:511)
07-02 18:04:31.170: E/AndroidRuntime(32619):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
07-02 18:04:31.170: E/AndroidRuntime(32619):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:558)
07-02 18:04:31.170: E/AndroidRuntime(32619):    at dalvik.system.NativeStart.main(Native Method)

奇怪的是，当我按下CashRegister父片段上的主页按钮时它不会崩溃，它只会在我第一次转到不同的父片段时抛出此异常。

This site表示FragmentManager在不允许的情况下尝试进行交易，但我无法找到可能的位置。当我删除onCreateView（）中的fm.beginTransaction.add（）调用时，它不会给出此错误，但是我无法在片段之间进行通信，因为在接口调用中没有要引用的父片段。 / p>

Answer 1

这不是你应该怎么做的。如果你想使用ViewPager，你需要调用ViewPager＃setPagerAdapter（）;在你的情况下，这个适配器将从FragmentPagerAdapter扩展，它使用getChildFragmentManager（）结果构建。

此代码应该为您完成工作。

// Add this to a files in your res\values folder <item type="id" name="view_pager" />
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    mViewPager = new ViewPager(activity);
    mViewPager.setId(R.id.view_pager);

    v = mViewPager;

    fm = getChildFragmentManager();

    custFrag = fm.findFragmentByTag(makeFragmentName(mViewPager.getId(), 0));
    if(custFrag == null) {
        custFrag = CashRegisterCustomerFragment.newInstance();
    }

    cartFrag = fm.findFragmentByTag(makeFragmentName(mViewPager.getId(), 1));
    if(cartFrag == null) {
        cartFrag = CashRegisterCartFragment.newInstance();
    }

    mViewPager.setPagerAdapter(new FragmentPagerAdapter(fm) {
        @Override
        public Fragment getItem(int position) {
            switch(position) {
                case 0:  return custFrag;
                case 1:  return cartFrag;
                default: return null;
            }
        }
        @Override
        public int getCount() {
            return 2;
        }
    });

    mActionBar = activity.getSupportActionBar();
    mActionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
    mActionBar.removeAllTabs();
    mActionBar.addTab(mActionBar.newTab().setText(getString(
        R.string.customer_list).setTabListener(mTabListener));
    mActionBar.addTab(mActionBar.newTab().setText(getString(
        R.string.items).setTabListener(mTabListener));

    int selectedTab = 0;
    if (savedInstanceState != null) {
        selectedTab = savedInstanceState.getInt("tab", 0);
    }
    mActionBar.setSelectedNavigationItem(selectedTab);

    return v;
}

// Very important.. this matches FragmentPagerAdapter code
private static String makeFragmentName(int viewId, long id) {
    return "android:switcher:" + viewId + ":" + id;
}

private ActionBar.TabListener mTabListener = new ActionBar.TabListener() {
    void onTabSelected(ActionBar.Tab tab, FragmentTransaction ft) {
        mViewPager.setCurrentItem(tab.getPosition());
    }
    void onTabReselected(ActionBar.Tab tab, FragmentTransaction ft) {
    }
    void onTabUnselected(ActionBar.Tab tab, FragmentTransaction ft) {
    }
};