Customizing SegmentedControl Divider Colors in Swift

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In this article, we will delve into the world of UISegmentedControl in iOS development. We will explore how to customize the default divider colors and address some potential issues that may arise.

Introduction to UISegmentedControl

UISegmentedControl is a user interface component used to create a control with two or more segments, each representing an option for the user to select. This component provides an easy-to-use alternative to implementing a view hierarchy to achieve similar functionality.

By default, UISegmentedControl features a horizontal divider between its segments, which separates them visually. However, we can customize this divider color and style using various methods.

The Issue: Changing Divider Color

The original poster asked how they could change the default divider color in their UISegmentedControl. They attempted to achieve this by setting the divider image properties directly on the control.

setDividerImage(UIColor.white.image(CGSize(width: 0.1, height: 0.1)),
               forLeftSegmentState: .normal,
               rightSegmentState: .normal,
               barMetrics: .default)

Although this approach works, it has an unexpected side effect. The divider takes the full height of the control regardless of any custom heights set.

Understanding the Divider Image Properties

Before we proceed with a solution, let’s understand what the dividerImage properties do:

forLeftSegmentState:, rightSegmentState: - These specify which state (normal or selected) the divider image should be displayed for each segment.
barMetrics: .default - This sets the overall bar metrics of the control, including the width and height.

By default, the divider takes up the full height of the control. When setting a custom divider image, it’s essential to adjust these properties accordingly.

A Custom Solution

One solution to this issue is to use a different approach: creating an UIImage with a transparent background that fills the specified segment size.

extension UIColor {
    func image(_ size: CGSize = CGSize(width: 1, height: 1)) -> UIImage {
        return UIGraphicsImageRenderer(size: size).image { rendererContext in
            self.setFill()
            rendererContext.fill(CGRect(origin: .zero, size: size))
        }
    }
}

setDividerImage(UIColor.clear.image(CGSize(width: 0.1, height: 20)), // Set the divider image to a transparent bar with a fixed height.
               forLeftSegmentState: .normal,
               rightSegmentState: .normal,
               barMetrics: .default)

In this revised approach, we create an UIImage that fills the specified segment size. We then set this custom image as the divider image using the setDividerImage method.

Additional Issue: Creating a Divider Between Segments

Another potential issue arises when using both approaches (changing the divider color and setting a custom divider height) together.

When you use both methods, a secondary divider is created next to the selected segment. This is not desired behavior in our case, as we want only one divider that spans across all segments, like Apple’s default implementation.

To solve this issue, we can create an UIImageView with a transparent background and position it above the UISegmentedControl. We’ll then set its size to match the segment height and update its contentMode property to adjust to the control’s content.

let dividerView = UIImageView()
dividerView.image = UIImage()
dividerView.contentMode = .scaleAspectFit

segmentedControl.addSubview(dividerView)
segmentedControl.sendSubviewToBack(dividerView) // Send it behind other views in the hierarchy.

// Set its size and update content mode:
segmentedControl.layoutMarginsForVisibleSegments = [.top, .bottom]
let constraint = NSLayoutConstraint(item: dividerView,
                                    attribute: .height,
                                    relatedBy: .equal,
                                    toItem: segmentedControl,
                                    attribute: .height,
                                    multiplier: 1.0,
                                    constant: 5) // Adjust this value as needed.
segmentedControl.addConstraint(constraint)

dividerView.backgroundColor = UIColor.clear

segmentedControl.sendSubviewToBack(dividerView)

By creating an UIImageView with a transparent background, we can position it above the control and set its size to match the segment height. We also send this view behind other views in the hierarchy using the sendSubviewToBack method.

Conclusion

Customizing segmented controls is quite straightforward, but sometimes, the desired behavior may not work out as expected due to unexpected side effects or issues with custom divider images.

In this article, we covered how to change the default divider color of a segmented control by creating a custom image. We also discussed some potential issues when using both approaches together and presented a solution to address these problems.

Additional Tips and Variations

Experiment with different barMetrics values (e.g., .compact, .default) to see how they affect your controls.
Consider adding more advanced effects, such as changing the divider color based on user preferences or customizing other aspects of the control’s behavior.

With these adjustments, you should now be able to create segmented controls that match your desired style and functionality.

Last modified on 2024-03-15