MBRoundProgressView.m

#import "MBRoundProgressView.h"
#define forcolor(x) x/255.0f

@interface MBRoundProgressView()  {
@private
    float _progress;
}
@end

@implementation MBRoundProgressView

#pragma mark -
#pragma mark Accessors

- (float)progress {
    return _progress;
}

- (void)setProgress:(float)progress {
    _progress = progress;
    [self setNeedsDisplay];
}

#pragma mark -
#pragma mark Lifecycle

- (id)init {
    return [self initWithFrame:CGRectMake(0.0f, 0.0f, 37.0f, 37.0f)];
}

- (id)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        self.backgroundColor = [UIColor clearColor];
		self.opaque = NO;
    }
    return self;
}

#pragma mark -
#pragma mark Drawing

- (void)drawRect:(CGRect)rect {
    
    CGRect allRect = self.bounds;
    CGRect circleRect = CGRectInset(allRect, 2.0f, 2.0f);
    
    CGContextRef context = UIGraphicsGetCurrentContext();
    
    // Draw background
    CGContextSetRGBStrokeColor(context, forcolor(150.0f), forcolor(150.0f), forcolor(150.0f), 1.0f); // white
    CGContextSetRGBFillColor(context, 1.0f, 1.0f, 1.0f, 0.1f); // translucent white
    CGContextSetLineWidth(context, 2.0f);
    CGContextFillEllipseInRect(context, circleRect);
    CGContextStrokeEllipseInRect(context, circleRect);
    
    // Draw progress
    CGPoint center = CGPointMake(allRect.size.width / 2, allRect.size.height / 2);
    CGFloat radius = (allRect.size.width - 4) / 2;
    CGFloat startAngle = - ((float)M_PI / 2); // 90 degrees
    CGFloat endAngle = (self.progress * 2 * (float)M_PI) + startAngle;
    CGContextSetRGBFillColor(context, forcolor(150.0f), forcolor(150.0f), forcolor(150.0f), 1.0f); // white
    CGContextMoveToPoint(context, center.x, center.y);
    CGContextAddArc(context, center.x, center.y, radius, startAngle, endAngle, 0);
    CGContextClosePath(context);
    CGContextFillPath(context);
}

@end