Question

I am trying to make vertical tabs using this code
in oncreate i try to add tabs
and in tabHandler its an button onclick to set which tab to view

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
     tabHost = (TabHost)findViewById(android.R.id.tabhost);



     TabSpec firstTabSpec = tabHost.newTabSpec("tid1");
     TabSpec secondTabSpec = tabHost.newTabSpec("tid2");
    firstTabSpec.setIndicator("First Tab Name").setContent(new         Intent(this,PageOne.class));
     secondTabSpec.setIndicator("Second Tab Name").setContent(new Intent(this,PageTwo.class));
    tabHost.addTab(firstTabSpec);
    tabHost.addTab(secondTabSpec);
}
public void tabHandler(View target){
    //artistButton.setSelected(false);
   // albumButton.setSelected(false);
    //songButton.setSelected(false);
    if(target.getId() == R.id.artist_id){
        tabHost.setCurrentTab(0);

       // artistButton.setSelected(true);
    } else if(target.getId() == R.id.album_id){
       tabHost.setCurrentTab(1);
       // albumButton.setSelected(true);
    } else if(target.getId() == R.id.song_id){
      tabHost.setCurrentTab(2);
       // songButton.setSelected(true);
    }
}

and this is the main.xml

<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:orientation="horizontal" 
    android:layout_width="fill_parent" android:layout_height="fill_parent">
    <FrameLayout android:layout_width="0dip" 
        android:layout_height="fill_parent" android:layout_weight="0.2">
    <TabWidget android:id="@android:id/tabs" 
            android:layout_width="fill_parent" 
            android:layout_height="wrap_content"
            android:visibility="gone"/>
        <LinearLayout android:layout_width="fill_parent"  
            android:layout_height="fill_parent"
            android:orientation="vertical">
            <Button android:layout_height="0dip" 
                android:layout_width="fill_parent" 
                android:layout_weight="1.0"

                android:id="@+id/artist_id" 
                android:onClick="tabHandler"/>
            <Button android:layout_height="0dip" 
                android:layout_width="fill_parent" 
                android:layout_weight="1.0"

                android:id="@+id/album_id" 
                android:onClick="tabHandler"/>
            <Button android:layout_height="0dip" 
                android:layout_width="fill_parent" 
                android:layout_weight="1.0"

                android:id="@+id/song_id" 
                android:onClick="tabHandler"/>
    </LinearLayout> 
</FrameLayout>       
<FrameLayout android:id="@android:id/tabcontent" 
    android:layout_width="0dip" 
    android:layout_height="fill_parent" android:layout_weight="0.8"/>

but it throw this exception on run

01-21 19:01:03.655: E/AndroidRuntime(1101): FATAL EXCEPTION: main
01-21 19:01:03.655: E/AndroidRuntime(1101): java.lang.RuntimeException: Unable to start activity      ComponentInfo{com.exampleexample.   .MainActivity}: java.lang.NullPointerException

when these two lines added:
tabHost.addTab(firstTabSpec);
tabHost.addTab(secondTabSpec);

but i dont know why

Answer 1

the problem was extending activity instead of extend TabActivity