Easily Add Rounded Corners in Interface Builder with @IBInspectable

Simple code approach

For programmatic UI you can set the corner radius directly:

view.layer.cornerRadius = 5

Storyboard method

Typically developers create an IBOutlet and set the radius in awakeFromNib or viewDidLoad:

@IBOutlet weak var customView: UIView!
override func viewDidLoad() {
    super.viewDidLoad()
    customView.layer.cornerRadius = 5
}

Runtime attributes

Using Interface Builder's Runtime Attributes you can set layer.cornerRadius without code, but key‑path typos and poor readability are common issues.

Best practice with @IBInspectable

Since Xcode 6 you can expose custom properties to Interface Builder with @IBInspectable. Adding an inspectable property to any UIView lets you edit the corner radius directly in the Attributes Inspector. @IBInspectable var customNumber: Int? After adding the property, the inspector shows a field where you can enter the value:

@IBInspectable supports the following types: Boolean Number String Point Size Rect Range Color Image nil

Swift extension implementation

Create a file UIView+O2CornerRadius.swift with the following extension:

import UIKit
extension UIView {
    @IBInspectable var cornerRadius: CGFloat {
        get { return layer.cornerRadius }
        set { layer.cornerRadius = newValue }
    }
}

This lets you set the corner radius for any view directly in Interface Builder, achieving low coupling and high cohesion.

Objective‑C category implementation

For Objective‑C you can add a category with a property backed by the layer’s corner radius:

// UIView+O2CornerRadius.h
@interface UIView (O2CornerRadius)
@property (nonatomic, assign) IBInspectable CGFloat cornerRadius;
@end

// UIView+O2CornerRadius.m
@implementation UIView (O2CornerRadius)
- (void)setCornerRadius:(CGFloat)cornerRadius {
    self.layer.cornerRadius = cornerRadius;
}
- (CGFloat)cornerRadius {
    return self.layer.cornerRadius;
}
@end

Both Swift and Objective‑C solutions allow you to configure rounded corners without extra code in view controllers.