Can't Set Calayer's Border Color

Can't set CALayer's border color

The problem is that you are running this code too soon (in viewDidLoad). Your cornerRadius calculation depends upon calculateButton.frame, but its value is not known at this time. Move your code into viewDidLayoutSubviews and I think you will find that it works as you expect.

CALayer: add a border only at one side

I made a right border using this:

leftScrollView.clipsToBounds = YES;

CALayer *rightBorder = [CALayer layer];
rightBorder.borderColor = [UIColor darkGrayColor].CGColor;
rightBorder.borderWidth = 1;
rightBorder.frame = CGRectMake(-1, -1, CGRectGetWidth(leftScrollView.frame), CGRectGetHeight(leftScrollView.frame)+2);

[leftScrollView.layer addSublayer:rightBorder];

How to make CALayer border alpha value different with the bgcolor

Can I make the alpha of the border different with the bgcolor?

Yes. You could do something like this:

CALayer * firstLayer = [[CALayer alloc] init];

[firstLayer setFrame:CGRectMake(100, 100, 100, 100)];

firstLayer.borderColor = [UIColor colorWithRed:1.0 green:1.0 blue:1.0 alpha:1.0].CGColor;
firstLayer.borderWidth = 3.0f;
firstLayer.backgroundColor = [UIColor colorWithRed:1.0 green:1.0 blue:1.0 alpha:0.5].CGColor;

Another approach would be to have a layer inside another layer of the same size. Give the outer layer the border thickness you want and make sure it's opacity is 100%. The second layer should have the fractional opacity:

CALayer * firstLayer = [[CALayer alloc] init];
CALayer * secondLayer = [[CALayer alloc] init];

[firstLayer setFrame:CGRectMake(100, 100, 100, 100)];
[secondLayer setFrame:CGRectMake(0, 0, 100, 100)];
[firstLayer addSublayer:secondLayer];

firstLayer.borderColor = [UIColor redColor].CGColor;
firstLayer.borderWidth = 1.0f;

secondLayer.backgroundColor = [UIColor redColor].CGColor;
secondLayer.opacity = 0.8f;

[self.view.layer addSublayer:firstLayer];

UIView's border color in Interface builder doesn't work?

It's possible to do this, but it's not a built-in feature. This is because the Color type in the User Defined Runtime Attributes panel creates a UIColor, but layer.borderColor holds a CGColorRef type. Unfortunately, there's no way to assign a CGColorRef type in Interface Builder.

However, this is possible through a proxy property. See Peter DeWeese's answer to a different question for a possible solution to this problem. His answer defines a category that allows a proxy color to be set through Interface Builder.

How to add a border just on the top side of a UIView

I consider subclassing UIView and overriding drawRect overkill here. Why not add an extension on UIView and add border subviews?

@discardableResult
func addBorders(edges: UIRectEdge,
                color: UIColor,
                inset: CGFloat = 0.0,
                thickness: CGFloat = 1.0) -> [UIView] {

    var borders = [UIView]()

    @discardableResult
    func addBorder(formats: String...) -> UIView {
        let border = UIView(frame: .zero)
        border.backgroundColor = color
        border.translatesAutoresizingMaskIntoConstraints = false
        addSubview(border)
        addConstraints(formats.flatMap {
            NSLayoutConstraint.constraints(withVisualFormat: $0,
                                           options: [],
                                           metrics: ["inset": inset, "thickness": thickness],
                                           views: ["border": border]) })
        borders.append(border)
        return border
    }

    if edges.contains(.top) || edges.contains(.all) {
        addBorder(formats: "V:|-0-[border(==thickness)]", "H:|-inset-[border]-inset-|")
    }

    if edges.contains(.bottom) || edges.contains(.all) {
        addBorder(formats: "V:[border(==thickness)]-0-|", "H:|-inset-[border]-inset-|")
    }

    if edges.contains(.left) || edges.contains(.all) {
        addBorder(formats: "V:|-inset-[border]-inset-|", "H:|-0-[border(==thickness)]")
    }

    if edges.contains(.right) || edges.contains(.all) {
        addBorder(formats: "V:|-inset-[border]-inset-|", "H:[border(==thickness)]-0-|")
    }

    return borders
}

    // Usage:         
    view.addBorder(edges: [.all]) // All with default arguments 
    view.addBorder(edges: [.top], color: .green) // Just Top, green, default thickness
    view.addBorder(edges: [.left, .right, .bottom], color: .red, thickness: 3) // All except Top, red, thickness 3

With this code you're not tied to your subclass too, you can apply it to anything and everything that inherits from UIView - reusable in your project, and any others. Pass in other arguments to your methods to define other colours and widths. Many options.

Add a border outside of a UIView (instead of inside)

Unfortunately, there isn't simply a little property you can set to align the border to the outside. It draws aligned to the inside because the UIViews default drawing operations draw within its bounds.

The simplest solution that comes to mind would be to expand the UIView by the size of the border width when applying the border:

CGFloat borderWidth = 2.0f;

self.frame = CGRectInset(self.frame, -borderWidth, -borderWidth);
self.layer.borderColor = [UIColor yellowColor].CGColor;
self.layer.borderWidth = borderWidth;

Runtime attributes border color

Actually, you are using wrong attribute.The, correct attribute is layer.borderColor.
But again it will not work because it is type of CGColor and from IB we can only assign UIColor, we can't assign CGColor.

Eihter you can simply do it programaticlly.

Or

You can create extension with type CGColor.

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