FragmentTabHost 设置错误

Question

我正在尝试使用FragmentTabHost 实现嵌套片段，但是我不断收到setup() 函数的错误。代码如下。

这是我的课程文件

public class ForumFragment extends Fragment{
private FragmentTabHost mTabHost;
public ForumFragment() {
    // Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
    View view = inflater.inflate(R.layout.fragment_forum,container,false);


    mTabHost = (FragmentTabHost) view.findViewById(android.R.id.tabhost);
    mTabHost.setup(getActivity(), getChildFragmentManager(),android.R.id.tabcontent);

    mTabHost.addTab(mTabHost.newTabSpec("Tab1").setIndicator("DBoard"), DiscussionBoardFragment.class, null);
    mTabHost.addTab(mTabHost.newTabSpec("Tab2").setIndicator("Events"), EventsFragment.class, null);
    mTabHost.addTab(mTabHost.newTabSpec("Tab3").setIndicator("HW Help"), HWHelpFragment.class, null);
    mTabHost.addTab(mTabHost.newTabSpec("Tab4").setIndicator("Classifieds"), ClassifiedsFragment.class, null);

    return view;

}

这是我的 XML 文件

<TabHost
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/tabhost">


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

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

        </TabWidget>

        <FrameLayout
            android:id="@android:id/tabcontent"
            android:layout_width="match_parent"
            android:layout_height="match_parent">

            <RelativeLayout
                android:id="@+id/DBoard"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:orientation="vertical"></RelativeLayout>

            <RelativeLayout
                android:id="@+id/Events"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:orientation="vertical"></RelativeLayout>

            <RelativeLayout
                android:id="@+id/HWHelp"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:orientation="vertical"></RelativeLayout>
            <RelativeLayout
                android:id="@+id/Classifieds"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:orientation="vertical"></RelativeLayout>

        </FrameLayout>
    </LinearLayout>

这是我收到的错误

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.app.FragmentTabHost.setup(android.content.Context, android.support.v4.app.FragmentManager, int)' on a null object reference
                                                                                     at com.ForumFragment.onCreateView(ForumFragment.java:30)
                                                                                     at android.support.v4.app.Fragment.performCreateView(Fragment.java:1962)
                                                                                     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
                                                                                     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1248)
                                                                                     at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738)
                                                                                     at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1613)
                                                                                     at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:517)
                                                                                     at android.os.Handler.handleCallback(Handler.java:739)
                                                                                     at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                     at android.os.Looper.loop(Looper.java:145)
                                                                                     at android.app.ActivityThread.main(ActivityThread.java:6897)
                                                                                     at java.lang.reflect.Method.invoke(Native Method)
                                                                                     at java.lang.reflect.Method.invoke(Method.java:372)
                                                                                     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1404)
                                                                                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1199)

Answer 1

改变

mTabHost.setup(getActivity(), getChildFragmentManager(),android.R.id.tabcontent);

到

mTabHost.setup(getActivity(), getSupportFragmentManager(),android.R.id.tabcontent);

Answer 2

您必须将您的片段转换为 android.support.v4.app.Fragment 因为您使用的是 android.support.v4.app.FragmentTabHost 并且它是 仅支持 android.support.v4.app.Fragment。

阅读这一行android.support.v4.app.FragmentTabHost.setup(android.content.Context, android.support.v4.app.FragmentManager, int)

Answer 3

问题出在这一行：
mTabHost = (FragmentTabHost) view.findViewById(android.R.id.tabhost);

您需要扩充自己的 R 文件，而不是 android.R。只需将其更改为：

mTabHost = (FragmentTabHost) view.findViewById(R.id.tabhost);

并在 XML 文件中将 <TabHost 更改为 <android.support.v4.app.FragmentTabHost

Answer 4

Android Studio 不提供依赖项，因此您必须手动导入它们。文件 > 项目结构 > 应用程序（在“模块”下）> 依赖项选项卡。点击底部的“+”添加一个库依赖；在本例中为“support-v4”。