Implementing a clock face in UIView - objective-c

Question

I'm trying to implement a clock face in UIView - without much luck. The problem is that the hands on the clock face end up in totally the wrong position (i.e. pointing to the wrong time). I'm pretty sure that the logic of my code is correct - but clearly there's something significantly wrong.
My test app is an iOS Single View Application. ViewController.h looks like this:
#import <UIKit/UIKit.h>
#interface Clock : UIView {
UIColor* strokeColour;
UIColor* fillColour;
float strokeWidth;
NSDate* clockTime;
CGPoint clockCentre;
float clockRadius;
}
- (id)initWithCentre:(CGPoint)centre
radius:(float)radius
borderWidth:(float)width
facecolour:(UIColor*)fill
handcolour:(UIColor*)handFill
time:(NSDate*)time;
#end
#interface ViewController : UIViewController
#end
and ViewController.m looks like this:
#import "ViewController.h"
#implementation Clock
- (id)initWithCentre:(CGPoint)centre
radius:(float)radius
borderWidth:(float)width
facecolour:(UIColor*)fill
handcolour:(UIColor*)handFill
time:(NSDate*)time {
CGRect frame = CGRectMake(centre.x-radius,
centre.y-radius,
radius*2,
radius*2);
if (self = [super initWithFrame:frame]) {
// Initialization code
strokeColour = fill;
fillColour = handFill;
strokeWidth = width;
clockRadius = radius;
clockTime = time;
clockCentre.x = frame.size.width/2;
clockCentre.y = frame.size.height/2;
}
return self;
}
- (void)drawRect:(CGRect)rect {
double red, green, blue, alpha;
CGRect circleRect;
circleRect.origin.x = rect.origin.x+strokeWidth;
circleRect.origin.y = rect.origin.y+strokeWidth;
circleRect.size.width = rect.size.width - (strokeWidth*2);
circleRect.size.height = rect.size.height - (strokeWidth*2);
CGContextRef contextRef = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(contextRef, strokeWidth);
[fillColour getRed:&red green:&green blue:&blue alpha:&alpha];
CGContextSetRGBFillColor(contextRef, red, green, blue, alpha);
[strokeColour getRed:&red green:&green blue:&blue alpha:&alpha];
CGContextSetRGBStrokeColor(contextRef, red, green, blue, alpha);
CGContextFillEllipseInRect(contextRef, circleRect);
CGContextStrokeEllipseInRect(contextRef, circleRect);
CGContextSetLineWidth(contextRef, strokeWidth);
[strokeColour getRed:&red green:&green blue:&blue alpha:&alpha];
CGContextSetRGBStrokeColor(contextRef, red, green, blue, alpha);
float hourAngle, minuteAngle, secondAngle, angle;
double endX, endY;
NSCalendar *cal = [[NSCalendar alloc]initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
NSUInteger units = NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
NSDateComponents *components = [cal components:units fromDate:clockTime];
hourAngle = (components.hour /12.0) * M_PI * 2.0;
minuteAngle = (components.minute / 60.0) * M_PI * 2.0;
secondAngle = (components.second / 60.0) * M_PI * 2.0;
//minute hand
angle = minuteAngle;
endX = cos(angle) * (clockRadius*0.85) + clockCentre.x;
endY = sin(angle) * (clockRadius*0.85) + clockCentre.y;
CGContextMoveToPoint(contextRef,clockCentre.x,clockCentre.y);
CGContextAddLineToPoint(contextRef,endX,endY);
CGContextStrokePath(contextRef);
//hour hand
angle = hourAngle;
endX = cos(angle) * (clockRadius*0.65) + clockCentre.x;
endY = sin(angle) * (clockRadius*0.65) + clockCentre.y;
CGContextSetLineWidth(contextRef, strokeWidth*1.5);
CGContextMoveToPoint(contextRef,clockCentre.x,clockCentre.y);
CGContextAddLineToPoint(contextRef,endX,endY);
CGContextStrokePath(contextRef);
}
#end
#interface ViewController ()
#end
#implementation ViewController
- (UIView*)drawClockFaceWithCentre:(CGPoint)centre
radius:(float)radius
time:(NSDate*)time
colour:(UIColor*)colour
backgroundColour:(UIColor*)bgcolour {
UIView* clock = [[Clock alloc]initWithCentre:centre
radius:radius
borderWidth:6.0
facecolour:bgcolour
handcolour:colour
time:time];
clock.backgroundColor = [UIColor clearColor];
return clock;
}
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
CGPoint centre;
centre.x=200;
centre.y=200;
[self.view addSubview:[self drawClockFaceWithCentre:centre
radius:100
time:[NSDate date]
colour:[UIColor blackColor]
backgroundColour:[UIColor whiteColor]]];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
#end
I'm sure it's something very simple that I've done wrong - a mistake in my maths. Can anyone see the bug (and any other suggestions for improvements that could be made would be welcome, bearing in mind (of course) that this is just a simple test harness).

Answer 1

As I wrote in the comment, consider dropping doing everything in drawRect and use layers. Also, instead of calculating trigonometry to draw correct path, consider just drawing hands at 12:00 and transform rotate them with correct angle. You could do it like this in init...
CAShapeLayer *faceLayer = [CAShapeLayer layer];
faceLayer.frame = self.bounds;
faceLayer.fillColor = [UIColor whiteColor].CGColor;
faceLayer.strokeColor = [UIColor blackColor].CGColor;
faceLayer.path = [UIBezierPath bezierPathWithOvalInRect:faceLayer.bounds].CGPath;
faceLayer.lineWidth = 3.0;
[self.layer addSublayer:faceLayer];
CGPoint middle = CGPointMake(CGRectGetMidX(self.bounds), CGRectGetMidY(self.bounds));
NSCalendar *cal = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
NSUInteger units = NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
NSDateComponents *components = [cal components:units fromDate:time];
UIBezierPath *path = [UIBezierPath bezierPath];
[path moveToPoint:middle];
[path addLineToPoint:CGPointMake(middle.x, middle.y-radius*0.5)];
CGFloat hourAreaAngle = (2*M_PI)/12.0;
CAShapeLayer *hourLayer = [CAShapeLayer layer];
hourLayer.frame = self.bounds;
hourLayer.strokeColor = [UIColor redColor].CGColor;
hourLayer.lineWidth = 3.0;
hourLayer.path = path.CGPath;
[self.layer addSublayer:hourLayer];
hourLayer.transform = CATransform3DMakeRotation((components.hour/12.0*(M_PI*2.0))+(hourAreaAngle*(components.minute/60.0)), 0.0, 0.0, 1.0);
[path removeAllPoints];
[path moveToPoint:middle];
[path addLineToPoint:CGPointMake(middle.x, middle.y-radius*0.8)];
CAShapeLayer *minuteLayer = [CAShapeLayer layer];
minuteLayer.frame = self.bounds;
minuteLayer.strokeColor = [UIColor blueColor].CGColor;
minuteLayer.lineWidth = 2.0;
minuteLayer.path = path.CGPath;
[self.layer addSublayer:minuteLayer];
minuteLayer.transform = CATransform3DMakeRotation(components.minute/60.0*(M_PI*2.0), 0.0, 0.0, 1.0);
[path removeAllPoints];
[path moveToPoint:middle];
[path addLineToPoint:CGPointMake(middle.x, middle.y-radius)];
CAShapeLayer *secondsLayer = [CAShapeLayer layer];
secondsLayer.frame = self.bounds;
secondsLayer.strokeColor = [UIColor greenColor].CGColor;
secondsLayer.lineWidth = 1.0;
secondsLayer.path = path.CGPath;
[self.layer addSublayer:secondsLayer];
secondsLayer.transform = CATransform3DMakeRotation(components.second/60.0*(M_PI*2.0), 0.0, 0.0, 1.0);
Note I put my colours and line widths because I'm lazy and didn't want to check your code :P.
If you want to update hands later, just store hands layers as variables and transform rotate them again (just remember to first transform to identity!).