motionBegan, setStroke and drawRect correct usage - ios

Question

I'm working through a challenge in Big Nerd Ranch's iOS Programming guide in a chapter on UIView subclassing.
I have some code below that draws concentric circles in random colors. And, upon a shake, it should change them all to red. It doesn't because after red is set, drawRect is called again and the random color loop is redone.
Would the correct way to implement this be to move the random color loop somewhere out of drawRect? Do I set a semaphore (messy) to make sure the loop only runs once?
Thanks for your advice.
- (void)setCircleColor:(UIColor *)clr
{
circleColor = clr;
[self setNeedsDisplay];
}
- (BOOL) canBecomeFirstResponder
{
return YES;
}
- (void)motionBegan:(UIEventSubtype)motion withEvent:(UIEvent *)event
{
if (motion == UIEventSubtypeMotionShake) {
[self setCircleColor:[UIColor redColor]];
}
}
-(void)drawRect:(CGRect)dirtyRect
{
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGRect bounds = [self bounds];
// Figure out the center of the bounds rectangle
CGPoint center;
center.x = bounds.origin.x + bounds.size.width / 2.0;
center.y = bounds.origin.y + bounds.size.height / 2.0;
float maxRadius = hypot(bounds.size.width, bounds.size.height) / 2.0;
CGContextSetLineWidth(ctx, 10);
// Set up an array of colors
UIColor *red = [UIColor redColor];
UIColor *green = [UIColor greenColor];
UIColor *yellow = [UIColor yellowColor];
NSArray *colors = [[NSArray alloc]initWithObjects:red, green, yellow, nil];
// Draw concentric circles from the outside in
for (float currentRadius = maxRadius; currentRadius > 0; currentRadius -= 20) {
CGContextAddArc(ctx, center.x, center.y, currentRadius, 0.0, M_PI * 2, YES);
// Random index for colors array
NSUInteger randomIndex = arc4random() % [colors count];
[self setCircleColor:[colors objectAtIndex:randomIndex]];
[[self circleColor] setStroke];
// Perform drawing; remove path
CGContextStrokePath(ctx);
}
NSString *text = #"You are getting sleepy.";
UIFont *font = [UIFont boldSystemFontOfSize:28];
CGRect textRect;
textRect.size = [text sizeWithFont:font];
// Let's put that string in the center of the view
textRect.origin.x = center.x - textRect.size.width / 2.0;
textRect.origin.y = center.y - textRect.size.height / 2.0;
[[UIColor blackColor] setFill];
// Draw a shadow
CGSize offset = CGSizeMake(4, 3);
CGColorRef color = [[UIColor darkGrayColor] CGColor];
CGContextSetShadowWithColor(ctx, offset, 2.0, color);
[text drawInRect:textRect withFont:font];
}
-(id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
[self setBackgroundColor:[UIColor clearColor]];
[self setCircleColor:[UIColor lightGrayColor]];
}
return self;
}
#end

Answer 1

Make a BOOL isSHake and cancel the random colors after you shake the device, the circles will remain red and you can reset that upon another action.