An overview of the role activities, fragments and intents play in Android app development.

1. Activities, Fragments,
and Events
CPTR322: Mobile Application Development
Henry Osborne

2. Topics Covered
•
•
•
•
•
•
•
The life cycle of an activity
Customizing the UI using fragments
Applying styles and themes to activities
Displaying activities as dialog windows
Understanding the concept of intents
Linking activities using intent objects
Displaying alerts using notifications

3. Understanding Activities

4. What are activities?
• A window that contains the UI of an application
• An application can have zero or more activities
• Main purpose is to interact with the user
• Life Cycle: the stages an activitiy goes through from the
moment it appears on the screen to the moment it’s
hidden.

5. Creating Activities
• To create an activity, a Java class that extends the Activity base class
is created.
import android.app.Activity;
…
public class Activity101Activity extends Activity {
…
}
• The activity class loads it UI component using the XML file defined in the
res/layout folder.

6. Declaring Activities
• Each activity in the application, must be declared in the
AndroidManifest.xml file.
<activity
android:label=“@string/app_name”
android:name=“.Activity101Activity”>
<intent-filter></intent-filter>
</activity>

7. Activity Base Class
onCreate() – Called when the activity is first created
onStart() – Called when the activity becomes visible to the user
onResume() – Called when the activity starts interacting with the user
onPause() – Called when the current activity is being paused and the
previous activity is being resumed
• onStop() – Called when the activity is no longer visible
• onDestroy() – Called before the activity is destroyed by the system
• onRestart() – Called when the activity has been stopped and is
restarting
•
•
•
•

8. Figure 1: Activity Life cycle

9. Applying Styles and Themes

10. Applying Dialog Theme
<application
android:icon=“@drawable/ic_launcher”
android:theme=“@android:style/Theme.Dialog”>
<activity
android:label=“@string/app_name”
android:name=“.Activity101Activity”>
<intent-filter></intent-filter>
</activity>
</application>

11. Hiding Activity Title
import android.view.Window;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.main);
}

12. Linking Activities Using Intents

13. Fragments

14. What is a Fragment?
A Fragment is a piece of an application's user interface or
behavior that can be placed in an Activity. Interaction with
fragments is done through FragmentManager, which can be
obtained via Activity.getFragmentManager() and
Fragment.getFragmentManager().

15. Figure 2: An example of how two UI modules defined by fragments can be combined into one
activity for a tablet design, but separated for a handset design.

16. Adding Fragments Dynamically
• It is more useful if fragments are created and added to activites
during runtime.
• Allows for a customizable UI
• E.g. If the application is running on a smartphone, you might fill
the activity with a single fragment; if the activity is running on a
tablet, you might then fill the activity with two or more
fragments.

17. Fragment Life Cycle
A fragment must always be embedded in an activity and
the fragment's lifecycle is directly affected by the host
activity's lifecycle. For example, when the activity is
paused, so are all fragments in it, and when the activity is
destroyed, so are all fragments.

18. Figure 3. The lifecycle of a fragment (while its activity is running).

19. Displaying Notifications

20. For important messages the
NotificationManager is used to display a
persistent message at the top of the device
(commonly known as the status bar,
sometimes referred to as the notification
bar)

21. Activities, Fragments,
and Events