Beginning Android

  spec.setContent(R.id.tab1);
  spec.setIndicator(Clock);
  tabs.addTab(spec);
  spec = tabs.newTabSpec(tag2);
  spec.setContent(R.id.tab2);
  spec.setIndicator(Button);
  tabs.addTab(spec);
  tabs.setCurrentTab(0);
 }
}

We find our TabHost via the familiar findViewById() method, then have it call setup(). After that, we get a TabSpec via newTabSpec(), supplying a tag whose purpose is unknown at this time. Given the spec, you call setContent() and setIndicator(), then call addTab() back on the TabHost to register the tab as available for use. Finally, you can choose which tab is the one to show via setCurrentTab(), providing the 0-based index of the tab.

The results can be seen in Figures 10-5 and 10-6.

Figure 10-5. The TabDemo sample application, showing the first tab

Figure 10-6. The same application, showing the second tab

Adding Them Up

TabWidget is set up to allow you to easily define tabs at compile time. However, sometimes, you want to add tabs to your activity during runtime. For example, imagine an email client where individual emails get opened in their own tab for easy toggling between messages. In this case, you don’t know how many tabs or what their contents will be until runtime, when the user chooses to open a message.

Fortunately, Android also supports adding tabs dynamically at runtime.

Adding tabs dynamically at runtime works much like the compile-time tabs previously shown, except you use a different flavor of setContent(), one that takes a TabHost.TabContentFactory instance. This is just a callback that will be invoked — you provide an implementation of createTabContent() and use it to build and return the Let’s take a look at an example (Fancy/DynamicTab).

First, here is some layout XML for an activity that sets up the tabs and defines one tab, containing a single button:

<?xml version='1.0' encoding='utf-8'?>
<LinearLayout xmlns:android='http://schemas.android.com/apk/res/android'
 android:orientation='vertical'
 android:layout_width='fill_parent'
 android:layout_height='fill_parent'>
 <TabHost android:id='@+id/tabhost'
  android:layout_width='fill_parent'
  android:layout_height='fill_parent'>
  <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:paddingTop='62px'>
   <Button android:id='@+id/buttontab'
    android:layout_width='fill_parent'
    android:layout_height='fill_parent'
    android:text='A semi-random button'
   />
  </FrameLayout>
 </TabHost>
</LinearLayout>

What we want to do is add new tabs whenever the button is clicked. That can be accomplished in just a few lines of code:

public class DynamicTabDemo extends Activity {
 @Override
 public void onCreate (Bundle icicle) {
  super.onCreate(icicle);
  setContentView(R.layout.main);
  final TabHost tabs = (TabHost)findViewById (R.id.tabhost);
  tabs.setup();
  TabHost.TabSpec spec = tabs.newTabSpec(buttontab);
  spec.setContent(R.id.buttontab);
  spec.setIndicator(Button);
  tabs.addTab(spec);
  tabs.setCurrentTab(0);
  Button btn = (Button)tabs.getCurrentView ().findViewById(R.id.buttontab);
  btn.setOnClickListener(new View.OnClickListener() {
   public void onClick(View view) {
    TabHost.TabSpec spec = tabs.newTabSpec(tag1);
    spec.setContent(new TabHost.TabContentFactory() {
     public View createTabContent(String tag) {