TabHost in Android

Some times we want to wrap multiple views in a single window and navigate throught them with a Tab Container. this can be done in Android using TabHost control. There are two ways to use a TabHost application in Android:

1.     Using the TabHost to navigate through multiple views within the same activity.

2.     Using the TabHost to navigate through Actual multiple Activities using intents.

Anatomy of Tabbed Application An activity with a TabHost may look like this:

The Activity consists of:

1.     A TabHost: the root element of the layout.

2.     The TabHost wraps a TabWidget which represents the tab bar.

3.     The TabHost wraps a FrameLayout which wraps the contents of each tab.

There are some rules that we must stick to when using a Tabbed activity:

1.     If the activity is of type TabActivity [optional] then the TabHost must have the id @android:id/tabhost.

2.     The TabWidget must have the id @android:id/tabs.

3.     The FrameLayout must have the id @android:id/tabcontent.

Now let's see an exaple to an activity with multiple tabs:  this is the layout file

<?xml version="1.0" encoding="utf-8"?>

	<TabHost android:layout_width="fill_parent"
	android:layout_height="fill_parent"

	android:id="@+id/tabHost"
	xmlns:android="http://schemas.android.com/apk/res/android"

	>
	<TabWidget

	android:layout_width="fill_parent"
	android:layout_height="wrap_content"

	android:id="@android:id/tabs"
	/>

	<FrameLayout
	android:layout_width="fill_parent"

	android:layout_height="fill_parent"
	android:id="@android:id/tabcontent"

	>
	<LinearLayout

	android:layout_width="fill_parent"
	android:layout_height="wrap_content"

	android:id="@+id/tab1"
	android:orientation="vertical"

	android:paddingTop="60px"
	>

	<TextView
	android:layout_width="fill_parent"

	android:layout_height="100px"
	android:text="This is tab1"

	android:id="@+id/txt1"
	/>

	</LinearLayout>

	<LinearLayout
	android:layout_width="fill_parent"

	android:layout_height="fill_parent"
	android:id="@+id/tab2"

	android:orientation="vertical"
	android:paddingTop="60px"

	>
	<TextView

	android:layout_width="fill_parent"
	android:layout_height="100px"

	android:text="This is tab 2"
	android:id="@+id/txt2"

	/>

	</LinearLayout>

	<LinearLayout
	android:layout_width="fill_parent"

	android:layout_height="fill_parent"
	android:id="@+id/tab3"

	android:orientation="vertical"
	android:paddingTop="60px"

	>
	<TextView

	android:layout_width="fill_parent"
	android:layout_height="100px"

	android:text="This is tab 3"
	android:id="@+id/txt3"

	/>

	</LinearLayout>
	</FrameLayout>

</TabHost>

then in the code of our activity class

	public void onCreate(Bundle savedInstanceState) {
	super.onCreate(savedInstanceState);

	setContentView(R.layout.main);
	TabHost tabHost=(TabHost)findViewById(R.id.tabHost);

	tabHost.setup();

	TabSpec spec1=tabHost.newTabSpec("Tab 1");
	spec1.setContent(R.id.tab1);

	spec1.setIndicator("Tab 1");

	TabSpec spec2=tabHost.newTabSpec("Tab 2");
	spec2.setIndicator("Tab 2");

	spec2.setContent(R.id.tab2);

	TabSpec spec3=tabHost.newTabSpec("Tab 3");
	spec3.setIndicator("Tab 3");

	spec3.setContent(R.id.tab3);

	tabHost.addTab(spec1);
	tabHost.addTab(spec2);

	tabHost.addTab(spec3);

}

Is going to look like this:

1.     We create tabs using TabSpecs class.

2.     We set the title of each tab using TabSpecs.setIndicator() method.

3.     We set the content of each tab using TabSpecs.setContent() method.

4.     if you use TabActivity to as a base class to your activity, you do not need to call TabHost.Setup() method.

We can add an icon to the title of the tab like this:

	TabSpec spec1=tabHost.newTabSpec("Tab 1");
	spec1.setContent(R.id.tab1);

	spec1.setIndicator("Tab1",getResources().getDrawable(R.drawable.flash));

TabSpec spec2=tabHost.newTabSpec("Tab 2");

	spec2.setIndicator("Tab2",getResources().getDrawable(R.drawable.sun));
	spec2.setContent(R.id.tab2);

	TabSpec spec3=tabHost.newTabSpec("Tab 3");

	spec3.setIndicator("Tab3",getResources().getDrawable(R.drawable.chart));
	spec3.setContent(R.id.tab3);

It will look like this:

we can also specify the indicator to be a view:

	TabSpec spec1=tabHost.newTabSpec("Tab 1");
	spec1.setContent(R.id.tab1);

	TextView txt=new TextView(this);
	txt.setText("Tab 1");

	txt.setBackgroundColor(Color.RED);
	spec1.setIndicator(txt);

Setting the content of tabs: we saw how to set the contents of tabs by specifying multiple layout resources to be displayed within the same activity.

what If we have multiple Activities in our application and we want to navigate between them using tabs ?

in this case we will have one activity as the root activity of the application. this activity will have the TabHost and will navigate to other activities using Intents.

Note: the root activity must inherit from TabActivity.

the root activity will have layout file like this:

	<?xml version="1.0" encoding="utf-8"?>
	<TabHost android:layout_width="fill_parent"

	android:layout_height="fill_parent"
	android:id="@android:id/tabhost"

	xmlns:android="http://schemas.android.com/apk/res/android"
	>

	<TabWidget
	android:layout_width="fill_parent"

	android:layout_height="wrap_content"
	android:id="@android:id/tabs"

	/>
	<FrameLayout

	android:layout_width="fill_parent"
	android:layout_height="fill_parent"

	android:id="@android:id/tabcontent"
	>

	</FrameLayout>
	</TabHost>

the other activities will have a simple layout consisting of a TextView. Now to the code of the root activity

	public class TabDemo extends TabActivity {
	/** Called when the activity is first created. */

	@Override
	public void onCreate(Bundle savedInstanceState) {

	super.onCreate(savedInstanceState);
	setContentView(R.layout.main);

TabHost tabHost=getTabHost();

	// no need to call TabHost.Setup()

	//First Tab
	TabSpec spec1=tabHost.newTabSpec("Tab 1");

	spec1.setIndicator("Tab1",getResources().getDrawable(R.drawable.sun));
	Intent in1=new Intent(this, Act1.class);

	spec1.setContent(in1);

	TabSpec spec2=tabHost.newTabSpec("Tab 2");
	spec2.setIndicator("Tab2",getResources().getDrawable(R.drawable.chart));

	Intent in2=new Intent(this,Act2.class);
	spec2.setContent(in2);

tabHost.addTab(spec2);

	tabHost.addTab(spec3);
	}

}

and the activity will look like this

Adding tabs at run-time:  

we can add tabs to TabHost at run-time using TabSpec.setContent(TabContentFactory) method. 

The TabContentFactory is an interface that requires the implementation of a callback method createTabContent(String tag) which returns the view to be added to the content of the tab. So in the last example if we changed code that adds the content of the second tab to this:

	TabSpec spec1=tabHost.newTabSpec("Tab 1");
	spec1.setIndicator("Tab1",getResources().getDrawable(R.drawable.sun));

spec1.setContent(new TabContentFactory() {

@Override

	public View createTabContent(String tag) {
	// TODO Auto-generated method stub

return (new AnalogClock(TabDemo.this));

	}
	});

the activity will look like this