How can I add a button in my iOS app that generates a countdown timer?

To add a button in your iOS app that generates a countdown timer, you can leverage the new controls introduced in iOS 18, which are built using WidgetKit. Here's a step-by-step guide based on the session "Extend your app’s controls across the system" from WWDC 2024:

1. Create a Control Widget:

   • Start by defining a control widget in your widget extension. This control will be a button that starts and stops the countdown timer.
   • Use the ControlWidget protocol to define your control. Provide the necessary information such as the title, symbol, and action to perform.

2. Define the Timer Toggle Control:

   • Create a type conforming to ControlWidget and define the control's configuration.
   • Provide a unique identifier, title, and state for the control.
   • Define the action to perform when the control is interacted with, such as starting or stopping the timer.

3. Customize the Control's Appearance:

   • Use the isOn argument to display different symbols when the timer is running or stopped.
   • Customize the value text to reflect the timer's state (e.g., "Running" or "Stopped").

4. Make the Control Configurable:

   • If you want to have multiple timers (e.g., for work and personal use), make the control user-configurable.
   • Use the AppIntentControlValueProvider protocol to allow users to select which timer the control should interact with.

5. Sync Across Devices:

   • Use the push notification API to handle state changes from different devices, ensuring the timer's state is consistent across all devices.

Here is a simplified example of how you might define such a control in Swift:

import WidgetKit
import SwiftUI

struct TimerControl: ControlWidget {
    var body: some View {
        ControlConfiguration {
            ControlContent {
                Label("Start Timer", systemImage: "timer")
            }
            .onTap {
                // Action to start the timer
                startTimer()
            }
        }
    }
    
    func startTimer() {
        // Implement your timer logic here
    }
}

For more detailed steps and code examples, you can refer to the session Extend your app’s controls across the system (03:11).

Relevant Sessions

• Extend your app’s controls across the system
• What’s new in SwiftUI

These sessions provide comprehensive guidance on building and customizing controls, including buttons and toggles, for your iOS app.