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1. Android Bootcamp
SESSION 9 – TOUCH EVENTS

2. Agenda
 Event Handlers & Event Listeners
 Building Menus
 Fling Gestures
 Multi Touch events
 Animation
 Styles
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3. Event Handlers and Event Listeners
 Most user interaction with an Android device is captured
by the system and sent to a corresponding callback
method.
 These events can be handled by extending the class
and overriding the methods, called event handlers.
 User interaction with View or ViewGroup objects can
also support event listeners.
 For example, the setOnClickListener() event listener can
be registered for a button and when it is pressed, the
onClick() method is called.
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4. Intercepting a Physical Key Press 4
Source: Android Cookbook Text Book (Refer Handout)

5. Intercepting a Physical Key Press
 The system first sends any KeyEvent to the appropriate callback method
in the in-focus activity or view.
 These callback methods are :
 onKeyUp(), onKeyDown(), onKeyLongPress()—Physical key press
callbacks.
 onTrackballEvent(), onTouchEvent()—Trackball and touchscreen press
callbacks
 onFocusChanged()—Called when the view gains or loses focus
 These can be overridden by the application to customize with different
actions.
 For example, to turn off the camera button (to avoid accidental
presses), just consume the event in the onKeyDown() callback method
for the Activity.
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6. Intercepting a Physical Key Press
 This is done by intercepting the method for the event
KeyEvent.KEYCODE_CAMERA and returning true:
 public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_CAMERA) {
return true; // consume event, hence do nothing on camera button
}
return super.onKeyDown(keyCode, event);
}
 By consuming the event, it does not get passed on to other Android
components.
 There are a few exceptions to this:
 The Power button and HOME key are intercepted by the system and do not reach the application for
customization.
 The BACK, MENU, HOME, and SEARCH keys should not intercept the KeyDown but instead the KeyUp.
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7. Building Menus
 A developer can implement three types of menus in Android
 Options menu—The main menu for an Activity that displays when the
MENU key is pressed.
 Context Menu—A floating list of menu items that displays when a view is
long pressed.
 Submenu—A floating list of menu items that displays when a menu item
is pressed.
 The Options menu is created the first time the MENU key is pressed in an
activity.
 This launches the onCreateOptionsMenu() method that usually contains
Menu methods, such as:
 menu.add(GROUP_DEFAULT, MENU_ADD, 0, "Add")
.setIcon(R.drawable.icon);
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8. Building Menus
 the onPrepareOptionsMenu() can be used if any of the menu options
need to change during run-time
 When an item from the options menu is clicked, the
onOptionsItemSelected() method is called.
 This passes the selected item ID, and a switch statement can be used to
determine which option was selected.
Utilizing Search KEY
 If an activity in the in-focus application is defined to be searchable, the
SEARCH key invokes it.
 The menu choice simply needs a call to onSearchRequested().
 The searchable activity ideally should be declared as singleTop launch
mode.
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9. Listening for Fling Gestures
 The possible gestures in the OnGestureListener interface are
 onDown()—Notifies when a tap down event occurs
 onFling()—Notifies when a tap down, movement, and matching up event occurs
 onLongPress()—Notifies when a long press occurs
 onScroll()—Notifies when a scroll occurs
 onShowPress()—Notifies when a tap down occurs before any movement or release
 onSingleTapUp()—Notifies when a tap up event occurs
 When only a subset of gestures are needed, the SimpleOnGestureListener class
can be extended instead.
 It returns false for any of the previous methods not explicitly implemented.
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10. Listening for Fling Gestures
 A fling consists of two events: a touch down (the first MotionEvent)
and a release (the second MotionEvent).
 Each motion event has a specified location on the screen given by
an (x,y) coordinate pair, where x is the horizontal axis and y is the
vertical axis.
 The (x,y) velocity of the event is also provided.
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11. Using Multi touch
 A multi touch event is when more than one pointer (such as a
finger) touches the screen at the same time.
 This is identified by using a touch listener OnTouchListener, which
receives multiple types of motion events:
 ACTION_DOWN—A press gesture has started with a primary pointer
(finger).
 ACTION_POINTER_DOWN—A secondary pointer (finger) has gone down.
 ACTION_MOVE—A change in press location has changed during a press
gesture.
 ACTION_POINTER_UP—A secondary pointer was released.
 ACTION_UP—A primary pointer was released, and the press gesture has
completed.
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12. Style Resource
 A style resource defines the format and look for a UI.
 A style can be applied to an individual View (from within a layout file) or to an entire Activity or
application (from within the manifest file).
 file location : res/values/filename.xml
The filename is arbitrary. The element's name will be used as the resource ID.
 resource reference: In XML: @[package:]style/style_name
 syntax:
<?xml version="1.0" encoding="utf-8"?>
<resources>
<style
name="style_name"
parent="@[package:]style/style_to_inherit">
<item
name="[package:]style_property_name"
>style_value</item>
</style>
</resources>
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13. Style Resource
 EXAMPLE:
XML file for the style (saved in res/values/):
<?xml version="1.0" encoding="utf-8"?>
<resources>
<style name="CustomText" parent="@style/Text">
<item name="android:textSize">20sp</item>
<item name="android:textColor">#008</item>
</style>
</resources>
XML file that applies the style to a TextView (saved in res/layout/):
<?xml version="1.0" encoding="utf-8"?>
<EditText
style="@style/CustomText"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Hello, World!" />
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14. Apply a theme to an Activity or application
 To set a theme for all the activities of your application, open the AndroidManifest.xml file and edit
the <application> tag to include the android:theme attribute with the style name. For example:
 <application android:theme="@style/CustomTheme">
 If you want a theme applied to just one Activity in your application, then add
the android:theme attribute to the <activity> tag instead.
 <activity android:theme="@style/CustomTheme">
 Just as Android provides other built-in resources, there are many pre-defined themes that you can
use, to avoid writing them yourself.
 For example, you can use the Dialog theme and make your Activity appear like a dialog box:
 <activity android:theme="@android:style/Theme.Dialog">
 if you want the background to be transparent, use the Translucent theme:
 <activity android:theme="@android:style/Theme.Translucent">
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15. Android Animation
 Android provides two types of animation: frame-by-frame and Tween animation.
 Frame by frame animation shows a sequence of pictures in order.
 It enables developers to define the pictures to display, and then show them like a slideshow
 Frame-by-frame animation first needs an animation-list element in the layout file
containing a list of item elements specifying an ordered list of the different pictures to
display.
 <?xml version="1.0" encoding="utf-8"?>
<animation-list xmlns:android="http://schemas.android.com/apk/res/android"
android:oneshot="false">
<item android:drawable="@drawable/anddev1" android:duration="200" />
<item android:drawable="@drawable/anddev2" android:duration="200" />
<item android:drawable="@drawable/anddev3" android:duration="200" />
</animation-list>
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16. Android Animation
 To display the frame-by-frame animation, set the animation to a
view’s background:
 ImageView im = (ImageView) this.findViewById(R.id.myanimated);
im.setBackgroundResource(R.anim.animated);
AnimationDrawable ad = (AnimationDrawable)im.getBackground();
ad.start();
 After the view background is set, a drawable can be retrieved by
calling getBackground() and casting it to
AnimationDrawable.Then, calling the start() method starts the
animation.
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17. Android Animation
 Tween animation uses a different approach that creates an animation
by performing a series of transformations on a single image.
 In Android, it provides access to the following classes that are the basis
for all the animations:
 AlphaAnimation—Controls transparency changes
 RotateAnimation—Controls rotations
 ScaleAnimation—Controls growing or shrinking
 TranslateAnimation—Controls position changes
 These four Animation classes can be used for transitions between
activities, layouts, views and so on.
 All these can be defined in the layout XML file as
<alpha>, <rotate>, <scale>,and <translate>.
 They all have to be contained within an AnimationSet <set>
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