首先:对于文本/代码墙感到抱歉，但我认为理解问题需要其中大部分内容。
我正在使用 ViewPager 和 TabHost 中的 Fragments 创建一个应用程序。 ViewPager 有一个自定义的 FragmentPagerAdapter，它将提供 ViewPager 中的各种页面。我遇到了自定义 FragmentPagerAdapter 开始将各种 Fragments 添加到 BackStack 的问题，但它在检查时失败了容器 ID(在本例中为 ViewPager 的 ID)与要添加的 Fragments 的 ID。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了最佳实践。以下可能是什么错误？
扩展主要 XML 布局的 Activity 。
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) {}
}
主要 XML 文件 my_activity.xml，包含 ViewPager、TabHost 和 ViewPager 的 fragment :
<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，onCreateView 会为每个自定义 Fragment 调用，它们会被膨胀并返回每个的根 View。下面是一个示例，用于 FilteredRecipesFragment。其他自定义 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;
}
}
最后是自定义的ViewPager和它的自定义的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 被膨胀后，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。这里是该方法的代码:
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，因为它是在 instantiateItem(ViewGroup, int) 调用中传递的 ID。在我的例子中，MyViewPager 实例的 ID 是 2131296319，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？
最佳答案
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;
}
您必须返回您的 Fragment 的新实例，而不是现有的实例，它已经有一个父级，因此，一个容器 assinged。删除您在布局中声明的 Fragment，并更改您的 getItem
@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;
}
关于android - FragmentPagerAdapter : IllegalStateException Can't change container ID of fragment，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/30694156/