[!TIP] Did you know Apple introduced UIButton.Configuration in iOS 15?

Using the new Configuration API you can create a button like this library achieves. Simply set showsActivityIndicator to show the indicator. You can do this and more in the configurationUpdateHandler:

let button = UIButton(configuration: .filled())

button.configurationUpdateHandler = { button in
    var currentConfig = button.configuration
    
    if isLoading {
        currentConfig?.baseBackgroundColor = .systemOrange
        currentConfig?.title = nil
    } else {
        currentConfig?.baseBackgroundColor = .systemGreen
        currentConfig?.title = "Click me!"
    }
    currentConfig?.buttonSize = .medium
    currentConfig?.showsActivityIndicator = isLoading
    
    button.configuration = currentConfig
}

UIButton Extension – UIActivityIndicatorView

A very simple library that provides a UIButton extension that enables use of UIActivityIndicatorView that replaces the title when enabled.

To enable the activity indicator it is as simple as the following

let button = UIButton()

button.activityIndicatorEnabled = true

You may also access the UIActivityIndicatorView to customise it under the read-only activityIndicatorView property.

Default configuration

For iOS 12 and below the activity indicator will be initialized with the UIActivityIndicatorView.Style.white style. For iOS 13 and higher it will be initialized with the UIActivityIndicatorView.Style.medium style.

Any time that activityIndicatorEnabled is set to true prior to display the activity indicator's color will be set to activityIndicatorColor – or titleColor(for: .normal) if that property is nil.