1. Cannon Game App Android How to Program
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Test drive the game

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5. 1$ indicates first arg, 2$ indicates second arg
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1$ indicates first arg, 2$ indicates second arg
d indicates we are formatting a decimal integer
f a floating point value
.1f floating point value with one digit after decimal

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7. Adding a custom component to a layout’s XML file
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Adding a custom component to a layout’s XML file
Must fully qualify the class name in the XML element.

8. Technologies Overview
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String formatting
Used with drawText and getString
Attaching a Custom View to a Layout
Extend class SurfaceView to create CannonView
Using the Resource Folder raw
Media files placed in res/raw
More Activity lifecycle methods
onPause called for current activity when another activity receives focus (used to suspend game)
onDestroy will release the app’s sound resources

9. Technologies Overview
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Overriding Activity method onTouchEvent
For testing which gesture was performed and processing it
Using GestureDetector and SimpleOnGestureListener
Recognize user actions that represent a series of MotionEvents (flings, double-taps, long presses, scrolls…)
Adding Sound with SoundPool and AudioManager
SoundPool loads, plays and unloads sounds.
Played with an audio stream
Uses setVolumeControlStream method

10. Technologies Overview
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Using Threads, SurfaceView and SurfaceHolder for frame-by-frame animation
This app performs its animations manually by updating game elements from separate thread of execution
Uses subclass Thread with a run method to update positions of game elements, then draw them
Use class SurfaceView – a subclass of View to which any thread can draw
Games often require complex logic
Should be performed in separate threads
Those threads need to draw to the screen
Manipulated via SurfaceHolder object, which gets a Canvas to draw on

11. Technologies Overview
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Simple Collision Detection
Used to determine if cannonball has collided with blocker or with section of target
Other more sophisticated frameworks
Drawing Graphics using Paint and Canvas
Canvas methods : Draw text, lines and circles
Canvas draws on View’s Bitmap
Paint object specifies drawing characteristics (color, thickness, etc.)

12. Building the App
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As mentioned sound files are stored in the app’s res/raw folder. To add them to an app
Right click the res folder, select New > Folder
Specify folder name raw and click Finish
Drag sound files to folder
Need to edit the AVDs and add the sound feature
May need to first find the .img files for the AVDs in .android/avd folder or just turn off Snapshot enabled
In lab, you may actually need to create a temp AVD
These app consists of 3 classes
Line
CannonGame (the activity subclass)
CannonView

13. NOTE: Made public so they can be changed, without methods..
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NOTE: Made public so they can be changed, without
methods..

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18. SimpleGestureListener is for GestureDetector objects.
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SimpleGestureListener is for GestureDetector
objects.

19. UML Diagram View SurfaceView SurfaceHolder.Callback Activity
CannonView
CannonView(Context, AttributeSet
onSizeChange(…)
+newGame()
+updatePositions(double)
+fireCannonball(MotionEvent)
+alignCannon(MotionEvent)
+drawGameElements(Canvas)
+showGameOverDialog(int)
+stopGame
surfaceChanged(SurfaceHolder,…)
surfaceCreated(SurfaceHolder)
surfaceDestroyed(SurfaceHolder)
CannonGame
onCreate(Bundle)
onPause()
onDestroy()
onTouchEvent(MotionEvent)
Thread
SimpleGestureListener
onDoubleTap(MotionEvent)
CannonThread
CannonThread(SurfaceHolder)
+setRunning
run()
Line
Line()
Activity
SoundPool
AlertDialog
Canvas
SurfaceHolder

20. Creating a new class in a new file
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Expand the project’s src node in Package Explorer
Right click the package (com.deitel.cannongame) and select New > Class to display New Java Class dialog
In the Name field, enter CannonView
In the Superclass field, enter android.view.View
Click Finish
Enter java code in the file

21. Packages for sound and drawing
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Packages for sound and drawing

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25. Stores reference to parent Activity, so we can display
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In this case, context is the Activity (CannonGame) to which CannonView is attached and attrs contain values set in the layout’s XML document
Stores reference to parent
Activity, so we can display
An AlertDialog in it’s GUI
thread

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The SurfaceHolder method - getHolder() returns the corresponding SurfaceHolder object for managing the SurfaceView
SurfaceHolder’s method addCallback stores the object (this) that implements SurfaceHolder.Callback
In other words, line 96 registers this (CannonView) as the object that implements SurfaceHolder.Callback to receive method calls that indicate when the SurfaceView is created, updated and destroyed.

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28. Only called once, since this app displays only in portrait mode
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Only called once, since this app
displays only in portrait mode
Sizes of all game elements
dependent on screen size

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31. The first game completes
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This is true only after
The first game completes
Start a new game

32. Called by CannonThread’s run method
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Called by CannonThread’s run method
New locations calculated
based on elapsed time
between previous and
current frames
Simple collision
detection, using
bounding box

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37. Event has the the double-tap position
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Event has the the double-tap position

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39. Very simple physics, no gravity
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Very simple physics,
no gravity

40. Draws on the SurfaceView using the Canvas that the
CannonThread obtains from the SurfaceView’s SurfaceHolder
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44. A dialog must be displayed from the GUI thread,
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A dialog must be displayed from the GUI thread,
so Activity’s method runOnUiThread is called and
passed an object of an anonymous inner class that
Implements Runnable.

45. Called by CannonGame’s onPause method
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Called by CannonGame’s onPause method
Called by CannonGame’s onDestroy method

46. Required to implement Interface SurfaceHolder.Callback
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Required to implement Interface SurfaceHolder.Callback
Empty, because
app always in portrait mode
or resumed

47. Wait until thread has stopped
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Request to stop thread
Wait until thread has stopped

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49. The Game Loop Only one thread at a time can draw to
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Only one thread at a time can draw to
A SurfaceView, so we must lock it
Ensures game operates at same speed
regardless of how fast device is (if device is faster, game elements will move less and vice versa)

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