Android : How to show Application Launcher Dialog when do tap on button

I am getting app launcher dialog when i do tap on Home button with two options to set as home app - first, default phone app and second mine app, using this:

Activity:

public class DefaultLaunchActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_launcher);
    }   
}

manifest.xml

    <activity
        android:name="com.def.launc.DefaultLaunchActivity"
        android:theme="@android:style/Theme.Wallpaper.NoTitleBar.Fullscreen"
        android:launchMode="singleTask"
        android:stateNotNeeded="true"
        >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.HOME" />
            <category android:name="android.intent.category.DEFAULT" />
        </intent-filter>         
    </activity>

But what, if i have to show Application Launcher Dialog whenever user do tap on button

btn.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // what to put here to show app launcher dialog         
            }
        });