Why do I get a null pointer exception from TabWidget?
I'm writing an android program in which I have an activity that uses tabs.
The Activity
public class UnitActivity extends TabActivity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
TabHost tabHost = getTabHost();
TabSpec spec;
Resources res = getResources();
LayoutInflater.from(this).inflate(R.layout.unit_view, tabHost.getTabContentView(), true);
spec = tabHost.newTabSpec("controls");
spec.setIndicator("Control", res.getDrawable(R.drawable.ic_tab_equalizer));
spec.setContent(R.id.txtview);
tabHost.addTab(spec);
}
}
The XML referenced by R.layout.unit_view
<?xml version="1.0" encoding="utf-8"?>
<TabHost xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@android:id/tabhost"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<LinearLayout
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"
android:padding="5dp">
<TextView android:id="@+id/txtview"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:gravity="bottom"
android:text="nullpointer this!" />
</FrameLayout>
</LinearLayout>
</TabHost>
As far as I can see I'm doing the same thing I see in the tabs1 api sample from the android sdk. I've tried "getLayoutInflator()" instead of "LayoutInflator.from(this)" with the same result.
If I replace the LayoutInflater line with "setContentView(R.layout.unit_view)" my program doesn't crash with a null pointer exception but my content is completely blank and empty. I get the tab and that's it.
I've checked to make sure R.layout.unit_view and tabHost are not null when it runs the LayoutInflater line and they seem to be fine. They're defenitely not null. I've also checked to make sure LayoutInflater.from(this) returns a valid layout inflater object and it does.
The logcat indicating the error says
E/AndroidRuntime( 541): java.lang.NullPointerException E/AndroidRuntime( 541): at android.widget.TabWidget.dispatchDraw(TabWidget.java:206) E/AndroidRuntime( 541): at android.view.ViewGroup.drawChild(ViewGroup.java:1529) E/AndroidRuntime( 541): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258) E/AndroidRuntime( 541): at android.view.ViewGroup.drawChild(ViewGroup.java:1529) E/AndroidRuntime( 541): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258) E/AndroidRuntime( 541): at android.view.ViewGroup.drawChild(ViewGroup.java:1529) E/AndroidRuntime( 541): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258) E/AndroidRuntime( 541): at android.view.ViewGroup.drawChild(ViewGroup.java:1529) E/AndroidRuntime( 541): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258) E/AndroidRuntime( 541): at android.view.ViewGroup.drawChild(ViewGroup.java:1529) E/AndroidRuntime( 541): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258) E/AndroidRuntime( 541): at android.view.ViewGroup.drawChild(ViewGroup.java:1529) E/AndroidRuntime( 541): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258) E/AndroidRuntime( 541): at android.view.View.draw(View.java:6538) E/AndroidRuntime( 541): at android.widget.FrameLayout.draw(FrameLayout.java:352) E/AndroidRuntime( 541): at android.view.ViewGroup.drawChild(ViewGroup.java:1531) E/AndroidRuntime( 541): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258) E/AndroidRuntime( 541): at android.view.ViewGroup.drawChild(ViewGroup.java:1529) E/AndroidRuntime( 541): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258) E/AndroidRuntime( 541): at android.view.View.draw(View.java:6538) E/AndroidRuntime( 541): at android.widget.FrameLayout.draw(FrameLayout.java:352) E/AndroidRuntime( 541): at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:1830) E/AndroidRuntime( 541): at android.view.ViewRoot.draw(ViewRoot.java:1349) E/AndroidRuntime( 541): at android.view.ViewRoot.performTraversals(ViewRoot.java:1114) E/AndroidRuntime( 541): at android.view.ViewRoot.handleMessage(ViewRoot.java:1633) E/AndroidRuntime( 541): at android.os.Handler.dispatchMessage(Handler.java:99) E/AndroidRuntime( 541): at android.os.Looper.loop(Looper.java:123) E/AndroidRuntime( 541): at android.app.ActivityThread.main(ActivityThread.java:4363) E/AndroidRuntime( 541): at java.lang.reflect.Method.invokeNative(Native Method) E/AndroidRuntime( 541): at java.lang.reflect.Method.invoke(Method.java:521) E/AndroidRuntime( 541): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860) E/AndroidRuntime( 541): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) E/AndroidRuntime( 541): at dalvik.system.NativeStart.main(Native Method) I/Process ( 61): Sending signal. PID: 541 SIG: 3 I/dalvikvm( 541): threadid=7: reacting to signal 3 I/dalvikvm( 541): Wrote stack trace to '/data/anr/traces.txt'
Anybody have any idea how I can get this content into a tab without crashing my application? My actual program is more complex and has more than one tab but I simplified it down to this in an attempt to find out why it's crashing but it still crashes and I don't know why.
If I don't use LayoutInflator my program doesn't crash but I don't get any content either, just tabs.
Answer
For those of you who are using a TabHost not inside a TabActivity, then be sure to call TabHost.setup(). Here's the documentation for it: http://developer.android.com/reference/android/widget/TabHost.html#setup() Not doing so will result in a NullPointerException when you try to add tabs to your tabhost.
The tutorial fails to mention that, so I thought I'd bring it to your attention to save you guys the time I spent looking for it.