在我的应用程序（android 2.1）中，我已成功使用Fragments添加了标签，并使用了Android兼容性库v4。
现在我想在其中一个片段选项卡中添加另一个选项卡，但是tabwidget会抛出NullPointerException，我在这里做错了什么？
logcat的：
05-08 12:58:57.060: W/dalvikvm(1371): threadid=3: thread exiting with uncaught exception (group=0x4001b188)
05-08 12:58:57.060: E/AndroidRuntime(1371): Uncaught handler: thread main exiting due to uncaught exception
05-08 12:58:57.100: E/AndroidRuntime(1371): java.lang.NullPointerException
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.widget.TabWidget.dispatchDraw(TabWidget.java:206)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewGroup.drawChild(ViewGroup.java:1529)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewGroup.drawChild(ViewGroup.java:1529)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewGroup.drawChild(ViewGroup.java:1529)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.View.draw(View.java:6538)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewGroup.drawChild(ViewGroup.java:1531)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewGroup.drawChild(ViewGroup.java:1529)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.View.draw(View.java:6538)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.support.v4.view.ViewPager.draw(ViewPager.java:1574)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewGroup.drawChild(ViewGroup.java:1531)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewGroup.drawChild(ViewGroup.java:1529)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewGroup.drawChild(ViewGroup.java:1529)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewGroup.drawChild(ViewGroup.java:1529)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.View.draw(View.java:6538)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.widget.FrameLayout.draw(FrameLayout.java:352)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewGroup.drawChild(ViewGroup.java:1531)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.View.draw(View.java:6538)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.widget.FrameLayout.draw(FrameLayout.java:352)
05-08 12:58:57.100: E/AndroidRuntime(1371): at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:1830)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewRoot.draw(ViewRoot.java:1349)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewRoot.performTraversals(ViewRoot.java:1114)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.view.ViewRoot.handleMessage(ViewRoot.java:1633)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.os.Handler.dispatchMessage(Handler.java:99)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.os.Looper.loop(Looper.java:123)
05-08 12:58:57.100: E/AndroidRuntime(1371): at android.app.ActivityThread.main(ActivityThread.java:4363)
05-08 12:58:57.100: E/AndroidRuntime(1371): at java.lang.reflect.Method.invokeNative(Native Method)
05-08 12:58:57.100: E/AndroidRuntime(1371): at java.lang.reflect.Method.invoke(Method.java:521)
05-08 12:58:57.100: E/AndroidRuntime(1371): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
05-08 12:58:57.100: E/AndroidRuntime(1371): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
05-08 12:58:57.100: E/AndroidRuntime(1371): at dalvik.system.NativeStart.main(Native Method)
//子标签片段
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
public class Tab3Fragment extends Fragment
{
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
if (container == null) {
// We have different layouts, and in one of them this
// fragment's containing frame doesn't exist. The fragment
// may still be created from its saved state, but there is
// no reason to try to create its view hierarchy because it
// won't be displayed. Note this is not needed -- we could
// just run the code below, where we would create and return
// the view hierarchy; it would just never be used.
return null;
}
return (LinearLayout)inflater.inflate(R.layout.subtab, container, false);
}
}
// subtab.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#4C4C4C" >
<TabHost
android:id="@android:id/tabhost"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:padding="2dp">
<LinearLayout
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:padding="5dp">
<TabWidget
android:id="@android:id/tabs"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
<FrameLayout
android:id="@android:id/tabcontent"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
</FrameLayout>
</LinearLayout>
</TabHost>
</LinearLayout>