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

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

TRANSCRIPT

Page 1: Activities, Fragments, and Events

Activities, Fragments, and Events

CPTR322: Mobile Application Development

Henry Osborne

Page 2: Activities, Fragments, and Events

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

Page 3: Activities, Fragments, and Events

Understanding Activities

Page 4: Activities, Fragments, and Events

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.

Page 5: Activities, Fragments, and Events

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.

Page 6: Activities, Fragments, and Events

Declaring Activities

• Each activity in the application, must be declared in the AndroidManifest.xml file.

<activityandroid:label=“@string/app_name”android:name=“.Activity101Activity”><intent-filter></intent-filter>

</activity>

Page 7: Activities, Fragments, and Events

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

Page 8: Activities, Fragments, and Events

Figure 1: Activity Life cycle

Page 9: Activities, Fragments, and Events

Applying Styles and Themes

Page 10: Activities, Fragments, and Events

Applying Dialog Theme

<applicationandroid: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>

Page 11: Activities, Fragments, and Events

Hiding Activity Title

import android.view.Window;

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

requestWindowFeature(Window.FEATURE_NO_TITLE);

setContentView(R.layout.main);

}

Page 12: Activities, Fragments, and Events

Linking Activities Using Intents

Page 13: Activities, Fragments, and Events

Fragments

Page 14: Activities, Fragments, and Events

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().

Page 15: Activities, Fragments, and Events

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.

Page 16: Activities, Fragments, and Events

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.

Page 17: Activities, Fragments, and Events

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.

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

Page 19: Activities, Fragments, and Events

Displaying Notifications

Page 20: Activities, Fragments, and Events

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)

Page 21: Activities, Fragments, and Events

Activities, Fragments, and Events