Problem running android HelloTabWidget example - NullPointerException on addTab()

Question

I've tried the Tab Layout example, and I've also fixed the few typos in the example (and added all the activities to the manifest). However, when I run it on the emulator I get a NullPointerException on the first line that says

tabHost.addTab(spec);

So my question, of course, is. What is wrong with the example that would cause this exception? I'm using Eclipse Galileo and set the target package as Android 1.5. So far I've had no other problems with the other examples on the android dev site.

package com.example.hellotabwidget;

import android.app.TabActivity;
import android.content.Intent;
import android.content.res.Resources;
import android.os.Bundle;
import android.widget.TabHost;

public class HelloTabWidget extends TabActivity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) throws RuntimeException {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    Resources res = getResources(); // Resource object to get Drawables
    TabHost tabHost = getTabHost();  // The activity TabHost
    TabHost.TabSpec spec;  // Reusable TabSpec for each tab
    Intent intent;  // Reusable Intent for each tab

    // Create an Intent to launch an Activity for the tab (to be reused)
    //final Context context = getApplicationContext();
    intent = new Intent().setClass(this, ArtistsActivity.class);

    // Initialize a TabSpec for each tab and add it to the TabHost
    spec = tabHost.newTabSpec("artists").setIndicator("Artists",
            res.getDrawable(R.drawable.ic_tab_artists))
            .setContent(intent);
    tabHost.addTab(spec); //******** NullPointerException after running this line

    // Do the same for the other tabs
    intent = new Intent().setClass(this, AlbumsActivity.class);
    spec = tabHost.newTabSpec("albums").setIndicator("Albums",
            res.getDrawable(R.drawable.ic_tab_artists))
            .setContent(intent);
    tabHost.addTab(spec);

    intent = new Intent().setClass(this, SongsActivity.class);
    spec = tabHost.newTabSpec("songs").setIndicator("Songs",
            res.getDrawable(R.drawable.ic_tab_artists))
            .setContent(intent);
    tabHost.addTab(spec);

    tabHost.setCurrentTabByTag("artists");
}
}

main.xml:

<?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: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"
        android:padding="5dp" />
</LinearLayout>
</TabHost>

Answer 1

Try this in your manifest:

<activity android:name=".AlbumsActivity"  android:label="@string/app_name"></activity> 
    <activity android:name=".ArtistsActivity"  android:label="@string/app_name"></activity> 
    <activity android:name=".SongsActivity"  android:label="@string/app_name"></activity> 

Answer 2

Just want to say thanks to all that posted here. Solved my problem (the same as everyone else here). It was very frustrating to get this to work. They should have really simplified the example much better.

To try to sum up the changes needed.

1. add the 3 activity lines Ngetha says.

2. Move all 3 activity classes to separate files. example I ended up using for my SongsActivity.java file (with eclipse error suggestions)

   package com.example.HelloTabWidget;
   import android.app.Activity;
   import android.os.Bundle;
   import android.widget.TextView;
   public class SongsActivity extends Activity {
   public void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       TextView textview = new TextView(this);
       textview.setText("This is the Songs tab");
       setContentView(textview);
   }
   }
   

3. I had to create a res\drawable directory and place all icons there plus I made 3 xml files for the icons such as "ic_tab_songs.xml"