The app has four types of event handlers. The first is the ClockFrame timer, which controls the animation. It is used in both interactive and non-interactive mode. In interactive mode it handles one click on a ball and in non-interactive mode it handles one flash of a ball.

Note that it uses procedures to handle the action that takes place during each of the modes. This is a good example of abstraction and modularity.

The handler for the play button starts a new round of the game. It increases the round number, generates a random sequence, displays the first frame in the sequence of flashes, and starts the ClockFrame timer. It uses the PlayOneFrame procedure to handle the details of what happens during one frame of the animation. Note that this is the same procedure that is called by the ClockFrame handler.

There are four handlers for ball touches but they all do the same exact thing. They set the CurBallTouched variable to their unique number, they toggle the frameToggle and they call ProcessBallTouched to handle the details of the action that occurs when a ball is clicked. Note that this is the same procedure that is called by the ClockFrame timer.

As you can see, both the play button and ball touched events use the same design pattern to control the animation -- the flashing of the balls. Then perform one frame of action and they start the ClockFrame timer, which controls the remaining frames.

The handler for the reset button simply reinitializes the state of the game.

Among other tasks this requires:

• Resetting the round to 0.
• Clearing the sequence
• Updating the labels and buttons.

The of MakeTheSeuqence procedure uses a simple while looop to create a random sequence of ball numbers, 1 through 4. The length of the sequence is controlled by the theRound argument.

The theRound argument will always be equal to the Round global variable. But using the argument here is an example of good procedure design. Well designed procedures should be modular and self-contained. Ideally, you shouldn't have to look outside the procedure block to understand what it does. By using the local argument here, we can see clearly that it is used to control the loop and the length of the sequence.

The of HighlightOneBall procedure simply turns the selected ball, indicated by the BallIndex argument, to black. It uses a standard if...elseif control structure.

The of PlayOneFrame procedure controls one frame of the animation in non-interactive mode, highlighting one ball every other time it is called, depending on the frameToggle variable. Note how the frameToggle's value is toggled (set from false to true or vice versa) at the end of the procedure.

The ball to be highlighted is selected from the Sequence as indicated by the SequenceIndex.

Note that it performs the highlighting only when frameToggle is false. When frameToggle is true, it unhighlights all the balls.

In addition to being called when the play button is clicked, this procedure is called repeatedly by the ClockFrame timer. Thus, every half second, it either highlight or unhighlights a ball, thereby controlling the animation.

When the SequenceIndex exceeds the length of the Sequence, this means the entire sequence has been displayed. In that case the timer is disabled and the game is put in interactive mode -- it is now the user's turn to match the sequence.

The ProcessBallClick procedure has the same basic structure as the PlayOneFrame procedure. When the frameToggle is true, it unhighlights the balls and disables the ClockFrame timer, thereby waiting for the user to click another ball, which will enable the timer.

When the frameToggle is false -- thus every other time the method is called -- it will hightlight the ball that was clicked and enable the timer. The ball will remain highlighted for as long as the next timer interval.

If the user clicked on the ball that matches the current ball in the Sequence, as determined by SequenceIndex, then the game continues. If the user's click does not match the sequence, the game is over.

The ProcessGameOver procedure resets the app to enable the user to try again. This means enabling and relabeling some of the buttons.