PAPB 04A EventHandling

Event Handling
Pemrograman Aplikasi Perangkat Bergerak
 Muhammad Aminul Akbar

Team Teaching PAPB
Contents
 Events
 Widgets and Event Handling
 Anonymous Event Listener
 Setting Activity as Event Listener
Events
Events
 Event: Action that occurs when user interacts with
widgets. An external stimulus your program can respond
to.
 e.g. clicks, typing, scrolling, etc.
 Common kinds of events include: Mouse motion /

tapping, Keys pressed, Timers expiring, Network data
available
 Event-driven programming: Overall execution of your
program is largely dictated by user events. - Commonly
used in graphical interface programs.
Click Event Scenario
event
public void doSomething() {

...
}
Responding Events
1. Write methods to handle each kind of event
("listener" methods).
2. Attach those listener methods to a particular
GUI widgets.
Note:
One listener is not limited to be attached to one widget. It can
be attached to any widgets for the same events.
Widgets and
Event Handling
Widgets: Views That Have
Events
 For a list of the widgets provided by Android, see the
android.widget package.
 Some Examples
 Button
 CheckBox
 DatePicker
 EditText
 ImageView
 Spinner (ComboBox)
 Or even ViewGroups may also have events
Adding Widget Objects to
Activity
 Before widgets and views are manipulatable
through Activity, widgets and views have to be
loaded into Activity using:
View v = findViewById(WIDGET_RESOURCE_ID);
 WIDGET_RESOURCE_ID is defined in layout XML

file, called after calling the setContentView()
method.
Adding Widget Objects to
Activity (2)
 In Layout XML file, give an unique ID to widgets:
<TextView android:id="@+id/textViewName" />
 In Activity onCreate() method, obtain the widgets using

findViewById() and cast the result to their appropriate type:
TextView nameView =
(TextView) findViewById(R.id.textViewName);
Event Handling
 Widgets (or Views) may have events associated on it
and developer may decide what events are going to be
handled and process.
 An event is handled by event listener object.
 Event listener object is ANY objects or even anonymous
objects that implements the event listener interface
 The listener object therefore can be registered to a
specific widgets to do something for a specified events
http://developer.android.com/guide/topics/ui/ui-events.html
Events listener Interface
 Several event listener Interface that handle specific
events are:
 View.OnClickListener (for handling "clicks" on a View),
 View.OnTouchListener (for handling screen touch events),
 View.OnKeyListener (for handling device key presses)
 A listener has an action method that being

executed when an event occurred to the attached
widget
http://developer.android.com/guide/topics/ui/ui-events.html
Event Handling
User Click
Event
 Event Handler is a listener object
which handle an event and do
some action based on what it
listen to. View Widget
 A listener is any objects that Button
implements the listener interface. onClick()
setOnClickListener()
 An Activity could act as an event
listener by implementing the interface
 A listener need to be set to a view Event Handler Object
or widget so that it would be able

to listen to an event occurred to
the view or widget it is assigned to View.OnClickListener
Setup a Button Click Event
Handling
 Step 1: Add View (Button) to Activity, cast it to their appropriate
type
 Button button = (Button) findViewById( buttonViewID )
 Step 2: Implement Event Handler…

 For button's click event means the event handler object should
implements the View.OnClickListener interface
 TWO OPTIONS – using a separate (specific) object to handle event(s)
that implements the interface, OR
 have the Activity containing the button do the event handling and
letting the Activity implements the interface
 Step 3: Register Event Handler to the button
 button.setOnClickListener( clickEventHandlerObject )
Event handling class
diagram
FIRST METHOD
SECOND METHOD (Preferred Way)
1: Handling Event in a Listener Object
 EVENT HANDLING CODE in separate object named myClickListener
// Create an anonymous implementation of OnClickListener STEP 2

private OnClickListener myClickListener = new OnClickListener() {
public void onClick(View v) {
// do something when the button is clicked
}
};
//Now inside your Activity class onCreate event method
protected void onCreate(Bundle savedValues) {
...
// STEP 1: Capture our button from layout
Button button = (Button)findViewById(R.id.corky);
// STEP 3: Register the onClick listener

// with the implementation above
button.setOnClickListener(myClickListener);
...
}
2: Let Activity Handle the
Event
 Here's the code to handle Button's click event
using the Activity itself
public class ExampleActivity extends Activity implements OnClickListener {
protected void onCreate(Bundle savedValues) {
...
Button button = (Button)findViewById(R.id.corky); // STEP 1
button.setOnClickListener(this); //STEP 2 – registration
}
// Implement the OnClickListener callback method

// STEP 3 – event handler
public void onClick(View v) {
// do something when the button is clicked
}
...
}
Questions?
Let's Code!
Hello
Mr. Head
 Buatlah aplikasi Android
Mr.Head, dimana
"komponen" Head dapat
ditampilkan/dihilangkan
melalui komponen Checkbox
 Clue:
 Use ImageViews in
ConstraintLayout
 Ubah property visibility dari
View.

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Event Handling

Pemrograman Aplikasi Perangkat Bergerak

 Muhammad Aminul Akbar

 Common kinds of events include: Mouse motion /

public void doSomething() {

 WIDGET_RESOURCE_ID is defined in layout XML

<TextView android:id="@+id/textViewName" />

 In Activity onCreate() method, obtain the widgets using

 A listener has an action method that being

or widget so that it would be able

 Step 2: Implement Event Handler…

// Create an anonymous implementation of OnClickListener STEP 2

// STEP 3: Register the onClick listener

// Implement the OnClickListener callback method

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