Objective: To create a mobile game: CannonGame App
1. Create a
new Android Project called CannonGame with package mdad.game and the
activity name as CannonController.
2. Open the
strings.xml file and add the following strings: (DO NOT modify the ones in italics)
<r<resources> <string name="app_name">CannonGame</string> <string name="hello_world">Hello world!</string> <string name="action_settings">Settings</string> <string name="results_format">Shots fired: %1$d\nTotal time: %2$.1f</string> <string name="reset_game">Reset Game</string> <string name="win">You win!</string> <string name="lose">You lose!</string> <string name="time_remaining_format">Time remaining: %.1f seconds</string> </resources>
3. Add the highlighted codes in the layout activity_cannon_controller.xml
<?xml version="1.0" encoding="utf-8"?> <android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent"> <mdad.game.CannonView android:background="@android:color/transparent" android:id="@+id/cannonView" android:layout_height="match_parent" android:layout_width="match_parent" xmlns:android="http://schemas.android.com/apk/res/android"/> </android.support.constraint.ConstraintLayout>
4. Create new folder raw in res folder and drag the 3 sound (.wav) files into it.
The sound files can be downloaded here
5. Create a
new Java class CannonModel, in the same package, as shown: (this is the class
to create lines and other shapes). Fill in the missing codes (non-italics portion)
papackage mdad.game; import android.graphics.Point; public class CannonModel { public Point start; // starting Point public Point end; // ending Point // default constructor initializes Points to (0, 0) public CannonModel() { start = new Point(0, 0); // start Point end = new Point(0, 0); // end Point } // end constructor }// end class
6. Create a new class called CannonView (same package name).
papackage mdad.game; import java.util.HashMap; import java.util.Map; import android.app.Activity; import android.app.AlertDialog; import android.content.Context; import android.content.DialogInterface; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import android.graphics.Point; import android.graphics.Rect; import android.media.AudioManager; import android.media.SoundPool; import android.util.AttributeSet; import android.view.MotionEvent; import android.view.Surface; import android.view.SurfaceHolder; import android.view.SurfaceView; public class CannonView extends SurfaceView implements SurfaceHolder.Callback { private CannonThread cannonThread; // controls the game loop private Activity activity; // to display Game Over dialog in GUI thread private boolean dialogIsDisplayed = false; // constants for game play public static final int TARGET_PIECES = 7; // sections in the target public static final int MISS_PENALTY = 2; // seconds deducted on a miss public static final int HIT_REWARD = 3; // seconds added on a hit // variables for the game loop and tracking statistics private boolean gameOver; // is the game over? private double timeLeft; // the amount of time left in seconds private int shotsFired; // the number of shots the user has fired private double totalElapsedTime; // the number of seconds elapsed // variables for the blocker and target private CannonModel blocker; // start and end points of the blocker private int blockerDistance; // blocker distance from left private int blockerBeginning; // blocker distance from top private int blockerEnd; // blocker bottom edge distance from top private int initialBlockerVelocity; // initial blocker speed multiplier private float blockerVelocity; // blocker speed multiplier during game private CannonModel target; // start and end points of the target private int targetDistance; // target distance from left private int targetBeginning; // target distance from top private double pieceLength; // length of a target piece private int targetEnd; // target bottom's distance from top private int initialTargetVelocity; // initial target speed multiplier private float targetVelocity; // target speed multiplier during game private int lineWidth; // width of the target and blocker private boolean[] hitStates; // is each target piece hit? private int targetPiecesHit; // number of target pieces hit (out of 7) // variables for the cannon and cannonball private Point cannonball; // cannonball image's upper-left corner private int cannonballVelocityX; // cannonball's x velocity private int cannonballVelocityY; // cannonball's y velocity private boolean cannonballOnScreen; // is the cannonball on the screen private int cannonballRadius; // cannonball radius private int cannonballSpeed; // cannonball speed private int cannonBaseRadius; // cannon base radius private int cannonLength; // cannon barrel length private Point barrelEnd; // the endpoint of the cannon's barrel private int screenWidth; // width of the screen private int screenHeight; // height of the screen // constants and variables for managing sounds private static final int TARGET_SOUND_ID = 0; private static final int CANNON_SOUND_ID = 1; private static final int BLOCKER_SOUND_ID = 2; private SoundPool soundPool; // plays sound effects private Map<Integer, Integer> soundMap; // maps IDs to SoundPool // Paint variables used when drawing each item on the screen private Paint textPaint; // Paint used to draw text private Paint cannonballPaint; // Paint used to draw the cannonball private Paint cannonPaint; // Paint used to draw the cannon private Paint blockerPaint; // Paint used to draw the blocker private Paint targetPaint; // Paint used to draw the target private Paint backgroundPaint; // Paint used to clear the drawing area // public constructor public CannonView(Context context, AttributeSet attrs) { super(context, attrs); // call super's constructor activity = (Activity) context; // register SurfaceHolder.Callback listener getHolder().addCallback(this); // initialize Lines and points representing game items blocker = new CannonModel(); // create the blocker as a Line target = new CannonModel(); // create the target as a Line cannonball = new Point(); // create the cannonball as a point // initialize hitStates as a boolean array hitStates = new boolean[TARGET_PIECES]; // initialize SoundPool to play the app's three sound effects soundPool = new SoundPool(1, AudioManager.STREAM_MUSIC, 0); // create Map of sounds and pre-load sounds soundMap = new HashMap<Integer, Integer>(); // create new HashMap soundMap.put(TARGET_SOUND_ID, soundPool.load(context, R.raw.target_hit, 1)); soundMap.put(CANNON_SOUND_ID, soundPool.load(context, R.raw.cannon_fire, 1)); soundMap.put(BLOCKER_SOUND_ID, soundPool.load(context, R.raw.blocker_hit, 1)); // construct Paints for drawing text, cannonball, cannon, // blocker and target; these are configured in method onSizeChanged textPaint = new Paint(); // Paint for drawing text cannonPaint = new Paint(); // Paint for drawing the cannon cannonballPaint = new Paint(); // Paint for drawing a cannonball blockerPaint = new Paint(); // Paint for drawing the blocker targetPaint = new Paint(); // Paint for drawing the target backgroundPaint = new Paint(); // Paint for drawing the target } // end CannonView constructor // called by surfaceChanged when the size of the SurfaceView changes, // such as when it's first added to the View hierarchy @Override protected void onSizeChanged(int w, int h, int oldw, int oldh) { super.onSizeChanged(w, h, oldw, oldh); screenWidth = w; // store the width screenHeight = h; // store the height cannonBaseRadius = h / 18; // cannon base radius 1/18 screen height cannonLength = w / 8; // cannon length 1/8 screen width cannonballRadius = w / 36; // cannonball radius 1/36 screen width cannonballSpeed = w * 3 / 2; // cannonball speed multiplier lineWidth = w / 24; // target and blocker 1/24 screen width // configure instance variables related to the blocker blockerDistance = w * 5 / 8; // blocker 5/8 screen width from left blockerBeginning = h / 8; // distance from top 1/8 screen height blockerEnd = h * 3 / 8; // distance from top 3/8 screen height initialBlockerVelocity = h / 2; // initial blocker speed multiplier blocker.start = new Point(blockerDistance, blockerBeginning); blocker.end = new Point(blockerDistance, blockerEnd); // configure instance variables related to the target targetDistance = w * 7 / 8; // target 7/8 screen width from left targetBeginning = h / 8; // distance from top 1/8 screen height targetEnd = h * 7 / 8; // distance from top 7/8 screen height pieceLength = (targetEnd - targetBeginning) / TARGET_PIECES; initialTargetVelocity = -h / 4; // initial target speed multiplier target.start = new Point(targetDistance, targetBeginning); target.end = new Point(targetDistance, targetEnd); // endpoint of the cannon's barrel initially points horizontally barrelEnd = new Point(cannonLength, h / 2); // configure Paint objects for drawing game elements textPaint.setTextSize(w / 20); // text size 1/20 of screen width textPaint.setAntiAlias(true); // smoothes the text cannonPaint.setStrokeWidth(lineWidth * 1.5f); // set line thickness blockerPaint.setStrokeWidth(lineWidth); // set line thickness targetPaint.setStrokeWidth(lineWidth); // set line thickness backgroundPaint.setColor(Color.WHITE); // set background color newGame(); // set up and start a new game } // end method onSizeChanged // reset all the screen elements and start a new game public void newGame() { // set every element of hitStates to false--restores target pieces for (int i = 0; i < TARGET_PIECES; ++i) hitStates[i] = false; targetPiecesHit = 0; // no target pieces have been hit blockerVelocity = initialBlockerVelocity; // set initial velocity targetVelocity = initialTargetVelocity; // set initial velocity timeLeft = 10; // start the countdown at 10 seconds cannonballOnScreen = false; // the cannonball is not on the screen shotsFired = 0; // set the initial number of shots fired totalElapsedTime = 0.0; // set the time elapsed to zero blocker.start.set(blockerDistance, blockerBeginning); blocker.end.set(blockerDistance, blockerEnd); target.start.set(targetDistance, targetBeginning); target.end.set(targetDistance, targetEnd); if (gameOver) { gameOver = false; // the game is not over cannonThread = new CannonThread(getHolder()); cannonThread.start(); } // end if } // end method newGame // called repeatedly by the CannonThread to update game elements private void updatePositions(double elapsedTimeMS) { double interval = elapsedTimeMS / 1000.0; // convert to seconds if (cannonballOnScreen) // if there is currently a shot fired { // update cannonball position cannonball.x += interval * cannonballVelocityX; cannonball.y += interval * cannonballVelocityY; // check for collision with blocker if (cannonball.x + cannonballRadius > blockerDistance && cannonball.x - cannonballRadius < blockerDistance && cannonball.y + cannonballRadius > blocker.start.y && cannonball.y - cannonballRadius < blocker.end.y) { cannonballVelocityX *= -1; // reverse cannonball's direction timeLeft -= MISS_PENALTY; // penalize the user // play blocker sound soundPool.play(soundMap.get(BLOCKER_SOUND_ID), 1, 1, 1, 0, 1f); } // end if // check for collisions with left and right walls else if (cannonball.x + cannonballRadius > screenWidth || cannonball.x - cannonballRadius < 0) cannonballOnScreen = false; // remove cannonball from screen // check for collisions with top and bottom walls else if (cannonball.y + cannonballRadius > screenHeight || cannonball.y - cannonballRadius < 0) cannonballOnScreen = false; // make the cannonball disappear // check for cannonball collision with target else if (cannonball.x + cannonballRadius > targetDistance && cannonball.x - cannonballRadius < targetDistance && cannonball.y + cannonballRadius > target.start.y && cannonball.y - cannonballRadius < target.end.y) { // determine target section number (0 is the top) int section = (int) ((cannonball.y - target.start.y) / pieceLength); // check if the piece hasn't been hit yet if ((section >= 0 && section < TARGET_PIECES) && !hitStates[section]) { hitStates[section] = true; // section was hit cannonballOnScreen = false; // remove cannonball timeLeft += HIT_REWARD; // add reward to remaining time // play target hit sound soundPool.play(soundMap.get(TARGET_SOUND_ID), 1, 1, 1, 0, 1f); // if all pieces have been hit if (++targetPiecesHit == TARGET_PIECES) { cannonThread.setRunning(false); showGameOverDialog(R.string.win); // show winning dialog gameOver = true; // the game is over } // end if } // end if } // end else if } // end if // update the blocker's position double blockerUpdate = interval * blockerVelocity; blocker.start.y += blockerUpdate; blocker.end.y += blockerUpdate; // update the target's position double targetUpdate = interval * targetVelocity; target.start.y += targetUpdate; target.end.y += targetUpdate; // if the blocker hit the top or bottom, reverse direction if (blocker.start.y < 0 || blocker.end.y > screenHeight) blockerVelocity *= -1; // if the target hit the top or bottom, reverse direction if (target.start.y < 0 || target.end.y > screenHeight) targetVelocity *= -1; timeLeft -= interval; // subtract from time left // if the timer reached zero if (timeLeft <= 0.0) { timeLeft = 0.0; gameOver = true; // the game is over cannonThread.setRunning(false); showGameOverDialog(R.string.lose); // show the losing dialog } // end if } // end method updatePositions // fires a cannonball public void fireCannonball(MotionEvent event) { if (cannonballOnScreen) // if a cannonball is already on the screen return; // do nothing double angle = alignCannon(event); // get the cannon barrel's angle // move the cannonball to be inside the cannon cannonball.x = cannonballRadius; // align x-coordinate with cannon cannonball.y = screenHeight / 2; // centers ball vertically // get the x component of the total velocity cannonballVelocityX = (int) (cannonballSpeed * Math.sin(angle)); // get the y component of the total velocity cannonballVelocityY = (int) (-cannonballSpeed * Math.cos(angle)); cannonballOnScreen = true; // the cannonball is on the screen ++shotsFired; // increment shotsFired // play cannon fired sound soundPool.play(soundMap.get(CANNON_SOUND_ID), 1, 1, 1, 0, 1f); } // end method fireCannonball // aligns the cannon in response to a user touch public double alignCannon(MotionEvent event) { // get the location of the touch in this view Point touchPoint = new Point((int) event.getX(), (int) event.getY()); // compute the touch's distance from center of the screen // on the y-axis double centerMinusY = (screenHeight / 2 - touchPoint.y); double angle = 0; // initialize angle to 0 // calculate the angle the barrel makes with the horizontal if (centerMinusY != 0) // prevent division by 0 angle = Math.atan((double) touchPoint.x / centerMinusY); // if the touch is on the lower half of the screen if (touchPoint.y > screenHeight / 2) angle += Math.PI; // adjust the angle // calculate the endpoint of the cannon barrel barrelEnd.x = (int) (cannonLength * Math.sin(angle)); barrelEnd.y = (int) (-cannonLength * Math.cos(angle) + screenHeight / 2); return angle; // return the computed angle } // end method alignCannon // draws the game to the given Canvas public void drawGameElements(Canvas canvas) { // clear the background canvas.drawRect(0, 0, canvas.getWidth(), canvas.getHeight(), backgroundPaint); // display time remaining canvas.drawText(getResources().getString( R.string.time_remaining_format, timeLeft), 30, 50, textPaint); // if a cannonball is currently on the screen, draw it if (cannonballOnScreen) canvas.drawCircle(cannonball.x, cannonball.y, cannonballRadius, cannonballPaint); // draw the cannon barrel canvas.drawLine(0, screenHeight / 2, barrelEnd.x, barrelEnd.y, cannonPaint); // draw the cannon base canvas.drawCircle(0, (int) screenHeight / 2, (int) cannonBaseRadius, cannonPaint); // draw the blocker canvas.drawLine(blocker.start.x, blocker.start.y, blocker.end.x, blocker.end.y, blockerPaint); Point currentPoint = new Point(); // start of current target section // initialize curPoint to the starting point of the target currentPoint.x = target.start.x; currentPoint.y = target.start.y; // draw the target for (int i = 1; i <= TARGET_PIECES; ++i) { // if this target piece is not hit, draw it if (!hitStates[i - 1]) { // alternate coloring the pieces yellow and blue if (i % 2 == 0) targetPaint.setColor(Color.YELLOW); else targetPaint.setColor(Color.BLUE); canvas.drawLine(currentPoint.x, currentPoint.y, target.end.x, (int) (currentPoint.y + pieceLength), targetPaint); } // end if // move curPoint to the start of the next piece currentPoint.y += pieceLength; } // end for } // end method drawGameElements // display an AlertDialog when the game ends private void showGameOverDialog(int messageId) { // create a dialog displaying the given String final AlertDialog.Builder dialogBuilder = new AlertDialog.Builder(getContext()); dialogBuilder.setTitle(getResources().getString(messageId)); dialogBuilder.setCancelable(false); // display number of shots fired and total time elapsed // add the additional targetPiecesHit variable dialogBuilder.setMessage(getResources().getString( R.string.results_format, shotsFired, totalElapsedTime)); dialogBuilder.setPositiveButton( R.string.reset_game, new DialogInterface.OnClickListener() { // called when "Reset Game" Button is pressed @Override public void onClick(DialogInterface dialog, int which) { dialogIsDisplayed = false; newGame(); // set up and start a new game } // end method onClick } // end anonymous inner class ); // end call to setPositiveButton activity.runOnUiThread( new Runnable() { public void run() { dialogIsDisplayed = true; dialogBuilder.show(); // display the dialog } // end method run } // end Runnable ); // end call to runOnUiThread } // end method showGameOverDialog // stops the game public void stopGame() { if (cannonThread != null) cannonThread.setRunning(false); } // end method stopGame // releases resources; called by CannonGame's onDestroy method public void releaseResources() { soundPool.release(); // release all resources used by the SoundPool soundPool = null; } // end method releaseResources // called when surface changes size @Override public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) { } // end method surfaceChanged // called when surface is first created @Override public void surfaceCreated(SurfaceHolder holder) { if (!dialogIsDisplayed) { cannonThread = new CannonThread(holder); cannonThread.setRunning(true); cannonThread.start(); // start the game loop thread } // end if } // end method surfaceCreated // called when the surface is destroyed @Override public void surfaceDestroyed(SurfaceHolder holder) { // ensure that thread terminates properly boolean retry = true; cannonThread.setRunning(false); while (retry) { try { cannonThread.join(); retry = false; } // end try catch (InterruptedException e) { } // end catch } // end while } // end method surfaceDestroyed // Thread subclass to control the game loop private class CannonThread extends Thread { private SurfaceHolder surfaceHolder; // for manipulating canvas private boolean threadIsRunning = true; // running by default // initializes the surface holder public CannonThread(SurfaceHolder holder) { surfaceHolder = holder; setName("CannonThread"); } // end constructor // changes running state public void setRunning(boolean running) { threadIsRunning = running; } // end method setRunning // controls the game loop @Override public void run() { Canvas canvas = null; // used for drawing long previousFrameTime = System.currentTimeMillis(); while (threadIsRunning) { try { canvas = surfaceHolder.lockCanvas(null); // lock the surfaceHolder for drawing synchronized(surfaceHolder) { long currentTime = System.currentTimeMillis(); double elapsedTimeMS = currentTime - previousFrameTime; totalElapsedTime += elapsedTimeMS / 1000.00; updatePositions(elapsedTimeMS); // update game state drawGameElements(canvas); // draw previousFrameTime = currentTime; // update previous time } // end synchronized block } // end try finally { if (canvas != null) surfaceHolder.unlockCanvasAndPost(canvas); } // end finally } // end while } // end method run } // end nested class CannonThread } // end class CannonView
7.1. In the CannonController class, add the following statements and methods in the appropriate places.
papackage mdad.game; import android.app.Activity; import android.media.AudioManager; import android.os.Bundle; import android.view.GestureDetector; import android.view.GestureDetector.SimpleOnGestureListener; import android.view.MotionEvent; public class CannonController extends Activity { private GestureDetector gestureDetector; // listens for double taps private CannonView cannonView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_cannon_controller); cannonView = (CannonView) findViewById(R.id.cannonView); // get the CannonView gestureDetector = new GestureDetector(this, gestureListener); setVolumeControlStream(AudioManager.STREAM_MUSIC); } SimpleOnGestureListener gestureListener = new SimpleOnGestureListener() { // called when the user double taps the screen public boolean onDoubleTap(MotionEvent e) { cannonView.fireCannonball(e); return true; } // }; // end gestureListener public void onPause() { super.onPause(); cannonView.stopGame(); }
protected void onDestroy() { super.onDestroy(); cannonView.releaseResources(); }
public boolean onTouchEvent(MotionEvent event) { int action = event.getAction(); // the user user touched the screen or dragged along the screen if (action == MotionEvent.ACTION_DOWN ||action == MotionEvent.ACTION_MOVE) { cannonView.alignCannon(event); } return gestureDetector.onTouchEvent(event); } }
