CGContextMoveToPoint moves to wrong position - ios

Question

I'm new to core graphics and I'm struggling with a simple task of putting a sweeping circle inside a square. The outcome I got looks like this:
The circle won't appear at the center of the square, and the size of the circle appears much smaller than I specified.
Below is my drawRect method for drawing the circle. I have put the printed-out variable values while debugging in the comments for your convenience. I also printed out the value passed to initWithFrame: frame=(0 0; 256 256). The frame is the orange square you see in the picture.
- (void)drawRect:(CGRect)rect {
CGContextRef context = UIGraphicsGetCurrentContext();
CGFloat midX = CGRectGetMidX(self.bounds); // bounds = (0 0; 256 256); midX = 128
CGFloat midY = CGRectGetMidY(self.bounds); // midY = 128
CGFloat radius = midY - 4; // radius = 124
// Outer grey pie
[endColor setFill];
CGContextMoveToPoint(context, midX, midY); // move to center
CGContextAddEllipseInRect(context, CGRectMake(midX - radius, midY - radius, radius * 2, radius * 2)); // adds a circle of radius = square_side_length - 4
CGContextFillPath(context); // fill the circle above with grey
// Show the clock
NSTimeInterval seconds = [[NSDate date] timeIntervalSince1970];
CGFloat mod = fmod(seconds, self.period);
CGFloat percent = mod / self.period;
[fillColor setFill];
CGFloat start = -M_PI_2;
CGFloat end = 2 * M_PI;
CGFloat sweep = end * percent + start;
CGContextMoveToPoint(context, midX, midY);
CGContextAddArc(context, midX, midY, radius, start, sweep, 0); // radius = square_side_length - 24
CGContextFillPath(context);
// Innermost white pie
radius -= 50; // radius = square_side_length - 54
[bgColor setFill]; // white
CGContextMoveToPoint(context, midX, midY);
CGContextAddEllipseInRect(context, CGRectMake(midX - radius, midY - radius, radius * 2, radius * 2));
CGContextFillPath(context);
}
And below is the code that adds the clock to its superview:
clock = [[ProgressClock alloc] initWithFrame:self.clockHolder.bounds // bounds=[0 0; 256 256]
period:[TOTPGenerator defaultPeriod]
bgColor:[UIColor whiteColor]
strokeColor:[UIColor colorWithWhite:0 alpha:0.2]
fillColor:[UIColor blueColor]
endColor:[UIColor grayColor]
shade:NO];
[self.clockHolder addSubview:clock];
Can anyone spot the mistake I made? Thanks in advance.

Answer 1

Thanks a lot to #originaluser2's comment, I have fixed this issue simply by moving the clock presenting logic from viewDidLoad to viewDidAppear and the clock showed up perfectly. There was nothing wrong with the drawing code I posted; however the auto-layout initialization and the animation of my clock happened in a sequence that gave my drawing canvas a wrong frame. By putting the drawing logic in viewDidAppear, we are guaranteed that all the auto-layout setup has been completed, thus frames are fixed, before continue onto drawing the circle.