Amazing corner radius outside color issue

Question

This is code that I added to new view controller:

- (void)viewDidLoad
{
    [super viewDidLoad];

    UIView *contentView = [[UIView alloc] initWithFrame:CGRectMake(50, 50, 200, 100)];
    [contentView setClipsToBounds:YES];
    [contentView setBackgroundColor:[UIColor blueColor]];
    [self.view addSubview:contentView];

    [[contentView layer] setBorderColor:[[UIColor lightGrayColor] CGColor]];
    [[contentView layer] setBorderWidth:1.0f];
    [[contentView layer] setCornerRadius:5.0f];
    [[contentView layer] setMasksToBounds:YES];
} 

The result:

If look at the corners we can see outside blue pixels:

Answer 1

You could use a CAShapeLayer :

- (void)viewDidLoad
{
    [super viewDidLoad];

    UIView *contentView = [[UIView alloc] initWithFrame:CGRectMake(50, 50, 200, 100)];
    [self.view addSubview:contentView];

    CAShapeLayer *subLayer = [[CAShapeLayer alloc] init];
    [subLayer setFillColor:[UIColor blueColor].CGColor];
    [subLayer setStrokeColor:[UIColor grayColor].CGColor];
    [subLayer setLineWidth:6.0];
    [subLayer setPath:[UIBezierPath bezierPathWithRoundedRect:contentView.bounds cornerRadius:5.0].CGPath];

    [contentView.layer addSublayer:subLayer];
}