Question

I have to add a small red dot to a UIButton. I set the color of custom UIButton using this method:

+ (UIImage *) imageFromColor:(UIColor *)color {
    CGRect rect = CGRectMake(0, 0, 1, 1);
    UIGraphicsBeginImageContext(rect.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetFillColorWithColor(context, [color CGColor]);
    //  [[UIColor colorWithRed:222./255 green:227./255 blue: 229./255 alpha:1] CGColor]) ;
    CGContextFillRect(context, rect);
    UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return img;
}

Then I have just to add a simple red dot to this button which is assumably done like this:

+ (UIImage *) addRedDot 
{
    CGRect rect = CGRectMake(0, 0, 1, 1);
    UIGraphicsBeginImageContext(rect.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetFillColorWithColor(context, [[UIColor redColor] CGColor]);
    //  [[UIColor colorWithRed:222./255 green:227./255 blue: 229./255 alpha:1] CGColor]) ;
    CGContextSetRGBStrokeColor(context, 1.0f, 0.0f, 0.0f, 1.0f);

    CGContextSetLineWidth(context, 2.0);
    CGContextStrokeEllipseInRect(context, CGRectMake(10, 11, 21, 21));

 //   CGContextFillRect(context, rect);
    UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return img;
}

But it just returns a white image..
this client code is:

   if ([dateStringToAssign isEqualToString:[self dateToString:[NSDate date]]]) 
            {

                [buttonToLay setBackgroundImage:[CommonUIUtility imageFromColor:[UIColor cyanColor]] 
                                  forState:UIControlStateNormal];


            }
            if([dbm hasEventsForDate:buttonToLay.ownedDate])
            {
                NSLog(@"Has events");
                [buttonToLay setBackgroundImage:[CommonUIUtility addRedDot] forState:UIControlStateNormal];

            }

What’s the right way to add a small red dot to existing CGContext?

Answer 1

You’re stroking an ellipse beyonds the bounds of the context you set up in this line:

CGContextStrokeEllipseInRect(context, CGRectMake(10, 11, 21, 21));

In order to have the ellipse show up, it needs to be within the bounds of your context, which appears to have size 1×1.