UIView with rounded corner and border has wrong ed

Question

I have a UIView and two subviews in it. The subviews have rounded corners and a border value. The issue I have is that the outer edges of the rounded border contain a thin line of the subview background color. I must be missing something??

UIView *outerView = [[UIView alloc] initWithFrame:CGRectMake(0, 50, 320, 320)];
[self.view addSubview:outerView];
outerView.backgroundColor = [UIColor whiteColor];

UIView *innerView1 = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 160, 320)];
[outerView addSubview:innerView1];
innerView1.backgroundColor = [UIColor blackColor];
innerView1.layer.borderWidth = 20;
innerView1.layer.borderColor = [UIColor whiteColor].CGColor;
innerView1.layer.cornerRadius = 20;
//innerView1.layer.masksToBounds = YES;

UIView *innerView2 = [[UIView alloc] initWithFrame:CGRectMake(160, 0, 160, 320)];
[outerView addSubview:innerView2];
innerView2.backgroundColor = [UIColor blackColor];
innerView2.layer.borderWidth = 20;
innerView2.layer.borderColor = [UIColor whiteColor].CGColor;
innerView2.layer.cornerRadius = 20;
//innerView2.layer.masksToBounds = NO;
//innerView2.clipsToBounds = YES;
//innerView2.layer.shouldRasterize = YES;

Answer 1

To work around the problem, set the background color of the subviews to clearColor and then draw the background color using the drawRect method of a custom view class. Here's the code for the view class.

@interface WorkAroundView : UIView
@end

@implementation WorkAroundView
- (void)drawRect:(CGRect)rect
{
    CGFloat margin = self.layer.borderWidth;
    CGRect  background;
    background.origin.x = margin;
    background.origin.y = margin;
    background.size.width  = self.bounds.size.width  - 2 * margin;
    background.size.height = self.bounds.size.height - 2 * margin;

    CGContextRef context = UIGraphicsGetCurrentContext();
    [[UIColor blackColor] set];
    CGContextFillRect( context, background );
}
@end

And here's how you would use the custom view class. The only real change here from what you posted is that the background color for the subviews is set to clearColor.

UIView *outerView = [[UIView alloc] initWithFrame:CGRectMake(360, 200, 320, 320)];
[self.view addSubview:outerView];
outerView.backgroundColor = [UIColor whiteColor];

WorkAroundView *innerView1 = [[WorkAroundView alloc] initWithFrame:CGRectMake(0, 0, 160, 320)];
innerView1.backgroundColor = [UIColor clearColor];
innerView1.layer.borderWidth = 20;
innerView1.layer.borderColor = [UIColor whiteColor].CGColor;
innerView1.layer.cornerRadius = 20;
[outerView addSubview:innerView1];

WorkAroundView *innerView2 = [[WorkAroundView alloc] initWithFrame:CGRectMake(160, 0, 160, 320)];
innerView2.backgroundColor = [UIColor clearColor];
innerView2.layer.borderWidth = 20;
innerView2.layer.borderColor = [UIColor whiteColor].CGColor;
innerView2.layer.cornerRadius = 20;
[outerView addSubview:innerView2];

Answer 2

add a bezier path around the corner

CAShapeLayer *subLayer = [[CAShapeLayer alloc] init];
[subLayer setFillColor:[UIColor clearColor].CGColor];
[subLayer setStrokeColor:[UIColor whiteColor].CGColor];
[subLayer setLineWidth:1.0];
[subLayer setPath:[UIBezierPath bezierPathWithRoundedRect:imageView.bounds cornerRadius:imageView.layer.cornerRadius].CGPath];
[imageView.layer addSublayer:subLayer];