Recently, I have been playing around with Android. Unit-testing your application on Android is slightly cumbersome: the class that you test cannot use any class from AndroidSDK, e.g. View or Activity.
As we will see in the example below, in many cases you can achieve a reasonable testability of your code.
We wish to create a simple game. The view should show playground in which there is several balls. For now we are interested in a snippet that would allow us moving those balls freely around playground.
To that end we create classes Playground and Ball. Playground serves as a facade for accessing Balls. Ball is an object that knows it's position, size and identity.
A naive implementation would look like this:
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| public class PlaygroundView extends View { | |
| private PlaygroundModel model; | |
| public MovingObjectsView(Context context, AttributeSet attrs) { | |
| super(context, attrs); | |
| } | |
| public void setModel(PlaygroundModel model) { | |
| this.model = model; | |
| } | |
| @Override | |
| protected void onDraw(Canvas canvas) { | |
| (...) | |
| } | |
| @Override | |
| public boolean onTouchEvent(MotionEvent event) { | |
| Position position = position(event); | |
| if (event.getAction() == MotionEvent.ACTION_DOWN) { | |
| Ball grabbedBall = model.ballGrabbed(position); | |
| moveStartPosition = position; | |
| } else if (event.getAction() == MotionEvent.ACTION_UP) { | |
| grabbedBall = null; | |
| } else { | |
| model.move(grabbedBall, vector(moveStartPosition, moveEndPostion)); | |
| moveStartPosition = moveEndPostion; | |
| } | |
| invalidate(); | |
| return true; | |
| } | |
| private Position position(MotionEvent event) { | |
| return new Position(event.getX(), event.getY()); | |
| } | |
| } |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| public class PlaygroundView extends View { | |
| private Hand hand = new NotGrabbingHand() | |
| public MovingObjectsView(Context context, AttributeSet attrs) { | |
| super(context, attrs); | |
| } | |
| public void setHand(Hand hand) { | |
| this.hand = hand; | |
| } | |
| @Override | |
| protected void onDraw(Canvas canvas) { | |
| (...) | |
| } | |
| @Override | |
| public boolean onTouchEvent(MotionEvent event) { | |
| Position position = position(event); | |
| if (event.getAction() == MotionEvent.ACTION_DOWN) { | |
| hand.dropAt(position); | |
| } else if (event.getAction() == MotionEvent.ACTION_UP) { | |
| hand.grabAt(position); | |
| } else { | |
| hand.moveTo(position); | |
| } | |
| invalidate(); | |
| return true; | |
| } | |
| private Position position(MotionEvent event) { | |
| return new Position(event.getX(), event.getY()); | |
| } | |
| } | |
| public class NormalHand implements Hand { | |
| private PlaygroundModel model; | |
| private Position moveStartPosition; | |
| private Ball ball; | |
| public NormalHand(PlaygroundModel model) { | |
| this.model = model; | |
| } | |
| @Override | |
| public void grabAt(Position position) { | |
| Ball grabbedBall = model.ballGrabbed(position); | |
| moveStartPosition = position; | |
| }; | |
| @Override | |
| public void dropAt(Position position) { | |
| grabbedBall = null; | |
| }; | |
| @Override | |
| public void moveTo(Position moveEndPosition) { | |
| model.move(grabbedBall, vector(moveStartPosition, moveEndPostion)); | |
| moveStartPosition = moveEndPostion; | |
| }; | |
| } | |
| public class NotGrabingHand implements Hand { | |
| @Override | |
| public void grabAt(Position position) { }; | |
| @Override | |
| public void dropAt(Position position) { }; | |
| @Override | |
| public void moveTo(Position position) { }; | |
| } |
