Adding Tabs Dynamically
The TabWidget in Android 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, and this blog post will show you how.
For compile-time-defined tabs, in your Java code, to set up tabs with contents provided in layout XML, you simply create a TabHost.TabSpec object and call setContent() on it, with the widget ID of the tab's contents:
[sourcecode language='java']
TabHost.TabSpec spec=tabs.newTabSpec("buttontab");
spec.setContent(R.id.buttontab);
spec.setIndicator("Button");
tabs.addTab(spec);
[/sourcecode]
Adding tabs dynamically at runtime works much the same way, 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 View that becomes the content of the tab.
Let's take a look at an example.
First, here is some layout XML for an activity that sets up the tabs and defines one tab, containing a single button:
[sourcecode language='xml']
android:layout_width="fill_parent"
android:layout_height="fill_parent">
android:layout_height="fill_parent">
android:layout_height="wrap_content"
/>
android:layout_height="fill_parent"
android:paddingTop="62px">
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:text="A semi-random button"
/>
[/sourcecode]
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:
[sourcecode language='java']
package com.commonsware.android.dynamictab;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.AnalogClock;
import android.widget.Button;
import android.widget.TabHost;
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) {
return(new AnalogClock(DynamicTabDemo.this));
}
});
spec.setIndicator("Clock");
tabs.addTab(spec);
}
});
}
}
[/sourcecode]
In our button's setOnClickListener() callback, we create a TabHost.TabSpec object and give it an anonymous TabHost.TabContentFactory. The factory, in turn, returns the View to be used for the tab -- in this case, just an AnalogClock. The logic for constructing the tab's View could be much more elaborate, such as using ViewInflate to construct a view from layout XML.
Initially, when the activity is launched, we just have the one tab:
But, if we click the button three times, though, we get three new tabs, each containing a clock:
While in this case we added new tabs based on button clicks, you could use any sort of event as the trigger for adding a tab: long-tap on a listbox entry, option menu selection, etc.
Mark Murphy is the founder of CommonsWare and is the author of _The Busy Coder's Guide to Android Development_, _The Busy Coder's Guide to *Advanced* Android Development_, and _Android Programming Tutorials_.