Displaying Alerts

Alerts in UIKit are implemented using UIAlertController with the .alert style to present critical information, prompt user input, or confirm actions. This document covers displaying alerts, adding text fields, and managing alert severity, including the severity property introduced in iOS 18 for Mac Catalyst.

Displaying Alerts to the User

Alerts are modal dialogs that interrupt the user flow to communicate important information or request a decision. They are created using UIAlertController with the preferredStyle set to .alert.

Key Components

UIAlertController: Manages the alert’s presentation and content.
UIAlertAction: Defines buttons (actions) with titles, styles, and handlers.
Presentation: Displayed modally, centered on iPhone and iPad (no popover required for .alert style).

Basic Example

swift

import UIKit

class ViewController: UIViewController {
    @IBAction func showAlert(_ sender: UIButton) {
        let alert = UIAlertController(title: "Warning", message: "Your session is about to expire.", preferredStyle: .alert)
        
        let okAction = UIAlertAction(title: "OK", style: .default) { _ in
            print("OK tapped")
        }
        let cancelAction = UIAlertAction(title: "Cancel", style: .cancel) { _ in
            print("Cancel tapped")
        }
        
        alert.addAction(okAction)
        alert.addAction(cancelAction)
        
        present(alert, animated: true, completion: nil)
    }
}

Key Points

Title and Message: Use title for a brief headline and message for details. Both are optional but recommended for clarity.
Actions: Add at least one UIAlertAction to dismiss the alert. The .cancel style is typically used for dismissal.
Presentation: Use present(_:animated:completion:) to show the alert modally.
iPad: Alerts are centered and do not require popover configuration.

Adding Text Fields to an Alert

Text fields can be added to alerts to collect user input, such as a name or password.

Implementation

Use addTextField(configurationHandler:) to add and configure text fields.

Example

swift

@IBAction func showTextFieldAlert(_ sender: UIButton) {
    let alert = UIAlertController(title: "Enter Name", message: "Please provide your name.", preferredStyle: .alert)
    
    alert.addTextField { textField in
        textField.placeholder = "Your name"
        textField.keyboardType = .default
        textField.autocapitalizationType = .words
    }
    
    let submitAction = UIAlertAction(title: "Submit", style: .default) { _ in
        if let text = alert.textFields?.first?.text {
            print("Entered: \(text)")
        }
    }
    let cancelAction = UIAlertAction(title: "Cancel", style: .cancel)
    
    alert.addAction(submitAction)
    alert.addAction(cancelAction)
    
    present(alert, animated: true, completion: nil)
}

Key Points

Accessing Input: Retrieve input via alert.textFields in the action handler.
Multiple Text Fields: Add multiple text fields by calling addTextField multiple times.
Configuration: Customize with properties like placeholder, isSecureTextEntry, or keyboardType.
Validation: Validate input in the handler or disable actions using isEnabled.

Dynamic Action Enabling

Disable the submit action until valid input is provided:

swift

alert.addTextField { textField in
    textField.placeholder = "Your name"
    NotificationCenter.default.addObserver(forName: UITextField.textDidChangeNotification, object: textField, queue: .main) { _ in
        submitAction.isEnabled = !(textField.text?.isEmpty ?? true)
    }
}
submitAction.isEnabled = false // Initially disabled

Changing the Severity of an Alert

In iOS 18, UIAlertController includes a severity property for Mac Catalyst apps, allowing developers to specify the alert’s severity using the UIAlertControllerSeverity enum (.default or .critical). For standard iOS apps on iPhone/iPad, severity is conveyed through action styles, language, and visual customizations, as no severity property exists.

Severity Property (Mac Catalyst, iOS 18+)

For Mac Catalyst apps, set the severity property to indicate the alert’s importance:

swift

@IBAction func showCriticalAlert(_ sender: UIButton) {
    let alert = UIAlertController(title: "Critical Error", message: "Data could not be saved.", preferredStyle: .alert)
    
    #if targetEnvironment(macCatalyst)
    alert.severity = .critical // Set severity for Mac Catalyst
    #endif
    
    let retryAction = UIAlertAction(title: "Retry", style: .default) { _ in
        print("Retry tapped")
    }
    let cancelAction = UIAlertAction(title: "Cancel", style: .cancel)
    
    alert.addAction(retryAction)
    alert.addAction(cancelAction)
    
    // Emphasize severity with tint (all platforms)
    alert.view.tintColor = .systemRed
    
    present(alert, animated: true, completion: nil)
}

Conveying Severity on iOS (iPhone/iPad)

For standard iOS apps, use these techniques:

Action Styles: Use .destructive for high-severity actions (e.g., delete), .default for neutral actions, and .cancel for dismissal.
Title and Message: Use urgent language for critical alerts (e.g., “Error” or “Warning”).
Tint Color: Adjust view.tintColor to emphasize severity (e.g., red for errors).

Example (iOS)

swift

@IBAction func showHighSeverityAlert(_ sender: UIButton) {
    let alert = UIAlertController(title: "Error", message: "Failed to save data. Retry?", preferredStyle: .alert)
    
    let retryAction = UIAlertAction(title: "Retry", style: .default) { _ in
        print("Retry tapped")
    }
    let deleteAction = UIAlertAction(title: "Delete", style: .destructive) { _ in
        print("Delete tapped")
    }
    let cancelAction = UIAlertAction(title: "Cancel", style: .cancel)
    
    alert.addAction(retryAction)
    alert.addAction(deleteAction)
    alert.addAction(cancelAction)
    
    alert.view.tintColor = .systemRed // Visual cue for severity
    
    present(alert, animated: true, completion: nil)
}

Key Points

Mac Catalyst Severity: Use alert.severity = .critical or .default for Mac Catalyst apps to indicate importance.
iOS Severity: Rely on .destructive actions, urgent language, and tintColor for iPhone/iPad apps.
Conditional Compilation: Use #if targetEnvironment(macCatalyst) to safely access severity only for Mac Catalyst.
Consistency: Follow iOS conventions (e.g., red for destructive actions) for user familiarity.

Best Practices

Clarity: Use concise titles and messages to communicate intent.
Minimal Actions: Limit to 2–3 actions to avoid overwhelming users.
Cancel Action: Include a .cancel action for dismissal, typically placed last.
Accessibility: Ensure text fields and actions are VoiceOver-compatible with descriptive labels.
Testing: Test on iPhone, iPad, and Mac Catalyst (if applicable) to verify behavior.
Severity: Use the severity property for Mac Catalyst or design cues for iOS to match the alert’s purpose.
Text Fields: Validate input and provide clear placeholders.

Limitations

Severity Availability: The severity property is exclusive to Mac Catalyst in iOS 18 and not available for standard iOS apps.
Customization: Alerts have limited visual customization to maintain system consistency.
Modal Nature: Alerts interrupt the user flow, so use sparingly for critical messages.
Single Cancel: Only one .cancel action is supported.

Summary

Alerts in UIKit, created with UIAlertController in .alert style, are used to display critical information or collect input via text fields. The severity property, available in iOS 18 for Mac Catalyst, allows setting .critical or .default severity, but standard iOS apps rely on action styles, language, and tint colors to convey severity. By following best practices, developers can create effective and accessible alerts for both iOS and Mac Catalyst environments.

Displaying Alerts ​