FragmentPagerAdapter：IllegalStateException 无法更改片段的容器 ID

Question

首先：抱歉翻墙了text/code，不过我觉得大部分都需要看懂问题了

我正在 ViewPager 和 TabHost 中使用 Fragments 创建一个应用程序。 ViewPager 有一个自定义 FragmentPagerAdapter，它将提供 ViewPager 中的各个页面。我运行遇到一个问题，自定义 FragmentPagerAdapter 开始将各种 Fragments 添加到 BackStack，但它在检查容器 ID（在在本例中，ViewPager) 的 ID 与要添加的 Fragments 的 ID 相对应。这些是不同的，因此程序失败。我对使用 Fragments 还很陌生，所以我不确定我的代码是否遵循最佳实践。以下可能是什么错误？

Activity，使主要 XML 布局膨胀。

public class MyActivity extends FragmentActivity implements TabHost.OnTabChangeListener, ViewPager.OnPageChangeListener{
    private MyViewPager                 mViewPager;
    private FragmentTabHost             mFragmentTabHost;

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.my_activity);
        setupViewPager();
        setupFragmentTabHost();
    }

    private void setupViewPager()
    {
        mViewPager = (MyViewPager) findViewById(R.id.my_pager);
    }

    private void setupFragmentTabHost()
    {
        mFragmentTabHost = (FragmentTabHost) findViewById(android.R.id.tabhost);
        mFragmentTabHost.setOnTabChangedListener(this);
        mFragmentTabHost.setup(this, getSupportFragmentManager(), android.R.id.tabcontent);

        mFragmentTabHost.addTab(mFragmentTabHost.newTabSpec("tab1").setIndicator("Tab 1", null), TabFragment.class, null);
        mFragmentTabHost.addTab(mFragmentTabHost.newTabSpec("tab2").setIndicator("Tab 2", null), TabFragment.class, null);
        mFragmentTabHost.addTab(mFragmentTabHost.newTabSpec("tab3").setIndicator("Tab 3", null), TabFragment.class, null);
    }

    @Override
    protected void onDestroy()
    {
    }

    public MyViewPager getMyPager()
    {
        return mViewPager;
    }

    @Override
    public void onTabChanged(String tabId) {
        int position = mFragmentTabHost.getCurrentTab();
        mViewPager.setCurrentItem(position);
    }

    @Override
    public void onPageSelected(int position)
    {
        mFragmentTabHost.setCurrentTab(position);
    }

    @Override
    public void onPageScrollStateChanged(int arg0) {}

    @Override
    public void onPageScrolled(int arg0, float arg1, int arg2) {}
}

主 XML 文件，my_activity.xml，包含 ViewPager、TabHost 和 ViewPager 的片段：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <android.support.v4.app.FragmentTabHost
        android:id="@android:id/tabhost"
        android:layout_width="match_parent"
        android:layout_height="match_parent" >

        <LinearLayout
            android:orientation="vertical"
            android:layout_width="match_parent"
            android:layout_height="match_parent" >

            <FrameLayout
                android:id="@android:id/tabcontent"
                android:layout_width="0dp"
                android:layout_height="0dp"
                android:layout_weight="0" />

            <com.mycompany.myapp.gui.mypager.MyViewPager
                android:id="@+id/my_pager"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:layout_weight="1" />

            <TabWidget 
                android:id="@android:id/tabs"
                android:orientation="horizontal"
                android:layout_width="match_parent"
                android:layout_height="wrap_content" />

        </LinearLayout>
    </android.support.v4.app.FragmentTabHost>

    <fragment
        android:name="com.mycompany.myapp.gui.mypager.FilteredRecipesFragment"
        android:id="@+id/filtered_recipes_fragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:focusable="true" />

    <fragment
        android:name="com.mycompany.myapp.gui.mypager.SelectedRecipesFragment"
        android:id="@+id/selected_recipes_fragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:focusable="true" />

    <fragment
        android:name="com.mycompany.myapp.gui.mypager.ShoppingListFragment"
        android:id="@+id/shopping_list_fragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:focusable="true" />

</LinearLayout>

请注意，为每个自定义 Fragment 调用 onCreateView，它们被膨胀并返回每个自定义的根 View。这是一个例子，FilteredRecipesFragment。其他习俗Fragments类似。

public class FilteredRecipesFragment extends Fragment {

    private FilteredRecipesListFragment mFilteredRecipesListFragment;
    private Button showRecipeFilterButton;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.filtered_recipes_fragment, container, false);
        mFilteredRecipesListFragment = (FilteredRecipesListFragment)
                getFragmentManager().findFragmentById(R.id.filtered_recipes_list_fragment);
        showRecipeFilterButton = (Button) rootView.findViewById(R.id.show_recipe_filter_dialog_button);
        showRecipeFilterButton.setOnClickListener(new RecipeFilterButtonListener());
        return rootView;
    }
}

最后，自定义 ViewPager 及其自定义 FragmentPagerAdapter，程序失败的地方。

public class MyViewPager extends ViewPager{

    private MyActivity mMyActivity;
    private MyPagerAdapter mMyPagerAdapter;

    public MyViewPager(Context context, AttributeSet attrs)
    {
        super(context, attrs);
        mMyActivity = (MyActivity) context;
        mMyPagerAdapter = new MyPagerAdapter(mMyActivity.getSupportFragmentManager(), mMyActivity);
        this.setAdapter(mMyPagerAdapter);
        this.setOnPageChangeListener(mMyActivity);
        this.setCurrentItem(PagerConstants.PAGE_SHOPPING_LIST); // Page 0
    }
}

MyPagerAdapter.java:

public class MyPagerAdapter extends FragmentPagerAdapter{

    private MyActivity mMyActivity;

    public MyPagerAdapter(FragmentManager fragmentManager, MyActivity myActivity)
    {
        super(fragmentManager);
        mMyActivity = myActivity;
    }

    @Override
    public Fragment getItem(int position)
    {
        switch (position) {
        case PagerConstants.PAGE_FILTER_RECIPES: // 0
            return mMyActivity.getSupportFragmentManager().findFragmentById(R.id.filtered_recipes_fragment);

        case PagerConstants.PAGE_SELECTED_RECIPES: // 1
            return mMyActivity.getSupportFragmentManager().findFragmentById(R.id.selected_recipes_fragment);

        case PagerConstants.PAGE_SHOPPING_LIST: // 2
            return mMyActivity.getSupportFragmentManager().findFragmentById(R.id.shopping_list_fragment);

        default:
            return null;
        }
    }

    @Override
    public int getCount()
    {
        return PagerConstants.NUMBER_OF_PAGES; // 3
    }

    @Override
    public CharSequence getPageTitle(int position)
    {
        return PagerConstants.PAGE_TITLES(position);
    }

}

一切似乎工作正常，但在每个自定义 Fragment 膨胀后，自定义 ViewPager 也开始添加它们。这是 Eclipse:

的堆栈输出

06-07 15:37:49.815: E/AndroidRuntime(793): java.lang.IllegalStateException: Can't change container ID of fragment FilteredRecipesFragment{4605b0e0 #0 id=0x7f09003f android:switcher:2131296318:0}: was 2131296319 now 2131296318
BackStackRecord.doAddOp(int, Fragment, String, int) line: 407   
BackStackRecord.add(int, Fragment, String) line: 389    
MyPagerAdapter(FragmentPagerAdapter).instantiateItem(ViewGroup, int) line: 99   
MyViewPager(ViewPager).addNewItem(int, int) line: 832   
MyViewPager(ViewPager).populate(int) line: 982  
MyViewPager(ViewPager).populate() line: 914 
MyViewPager(ViewPager).onMeasure(int, int) line: 1436   
MyViewPager(View).measure(int, int) line: 8171  
LinearLayout(ViewGroup).measureChildWithMargins(View, int, int, int, int) line: 3132
... More calls <snipped>

在 BackStackRecord.doAppOp 中失败，因为容器 ID（即 MyViewPager 的 ID 与 Fragment ID 不同。这是该方法的代码：

private void doAddOp(int containerViewId, Fragment fragment, String tag, int opcmd) {
    fragment.mFragmentManager = mManager;

    if (tag != null) {
        if (fragment.mTag != null && !tag.equals(fragment.mTag)) {
            throw new IllegalStateException("Can't change tag of fragment "
                    + fragment + ": was " + fragment.mTag
                    + " now " + tag);
        }
        fragment.mTag = tag;
    }

    if (containerViewId != 0) {
        if (fragment.mFragmentId != 0 && fragment.mFragmentId != containerViewId) {
            // IT FAILS HERE!
            throw new IllegalStateException("Can't change container ID of fragment "
                    + fragment + ": was " + fragment.mFragmentId
                    + " now " + containerViewId);
        }
        fragment.mContainerId = fragment.mFragmentId = containerViewId;
    }

    Op op = new Op();
    op.cmd = opcmd;
    op.fragment = fragment;
    addOp(op);
}

我知道容器 ID 是自定义 ViewPager 的 ID，因为在 instantiateItem(ViewGroup, int) 调用中传递的是它的 ID。在我的例子中，MyViewPager 实例的 ID 是 2131296319 而 Fragment 的 ID 是 2131296318 , 因此它失败了。

我这里哪里走错了？我对整个 ViewPager/FragmentPagerAdapter/Fragment 概念有什么误解？

Answer 1

问题在这里：

@Override
public Fragment getItem(int position)
{
     switch (position) {
     case PagerConstants.PAGE_FILTER_RECIPES: // 0
        return mMyActivity.getSupportFragmentManager().findFragmentById(R.id.filtered_recipes_fragment);

        case PagerConstants.PAGE_SELECTED_RECIPES: // 1
            return mMyActivity.getSupportFragmentManager().findFragmentById(R.id.selected_recipes_fragment);

        case PagerConstants.PAGE_SHOPPING_LIST: // 2
            return mMyActivity.getSupportFragmentManager().findFragmentById(R.id.shopping_list_fragment);

        default:
            return null;
}

您必须 return 您的 Fragment 的新实例，而不是现有实例，它已经有一个父实例，因此，一个容器被分配。删除您在布局中声明的 Fragments，并将您的 getItem 更改为

@Override
public Fragment getItem(int position)
{
    switch (position) {
    case PagerConstants.PAGE_FILTER_RECIPES: // 0
        return new FilteredRecipesFragment();

    case PagerConstants.PAGE_SELECTED_RECIPES: // 1
        return new SelectedRecipesFragment();

    case PagerConstants.PAGE_SHOPPING_LIST: // 2
        return new ShoppingListFragment()

    default:
        return null;
}

Answer 2

出现此问题的一个可能原因是您尝试将同一片段添加两次。下图

public void populateFragments() {
        Fragment fragment = new Fragment();
        //fragment is added for the first time
        addFragment(fragment);

        // fragment is added for the second time
        // This call will be responsible for the issue. The 
        addFragment(fragment);
    }

    public void addFragment(Fragment fragment) {
        FrameLayout frameLayout = AppView.createFrameLayout(context);
        view.addView(frameLayout);
        getSupportFragmentManager().beginTransaction().add(frameLayout.getId(), fragment).commit();
    }

FragmentPagerAdapter：IllegalStateException 无法更改片段的容器 ID

FragmentPagerAdapter: IllegalStateException Can't change container ID of fragment

android

android-fragments

android-viewpager