An easier way to manage alerts in SwiftUI

Jun 7, 2020 swiftui swiftui-presentation

In this post, we’ll look at an easier way to manage alerts in SwiftUI, in a way that lets us reuse functionality, reduce state management and present many different alerts with the same modifier.

TLDR;

If you find this post too long, I have added this to my SwiftUIKit library. You can find the source code here. Feel free to try it out and let me know what you think.

The basics

To present alerts in SwiftUI, you use the alert modifier that takes an isPresented binding and a content function (since this was written, more options have been added):

struct MyView: View {
    
    @State private var isAlertActive = false
    
    var body: some View {
        Button("Show alert", action: showAlert)
            .alert(isPresented: $isAlertActive, content: alert)
    }

    func alert() -> Alert {
        Alert(title: Text("Hello, world!"))
    }

    func showAlert() {
        isAlertActive = true
    }
}

This can become tricky when you have to present multiple alerts from the same screen or reuse alerts across an app. You may end up duplicating code, state, view builders etc.

I have therefore tried to find a way to handle alerts in a more reusable way, that requires less code and less state, while still being flexible to support both global and screen-specific alerts.

It all begins with a very simple state manager that I call AlertContext.

Alert context

Instead of managing state in every view that should present alerts, I use an AlertContext:

public class AlertContext: PresentationContext<Alert> {
    
    public override func content() -> Alert {
        contentView ?? Alert(title: Text(""))
    }
    
    public func present(_ provider: AlertProvider) {
        contentView = provider.alert
    }
}

As you can see, it contains code for presenting an Alert (which is just a view) or an AlertProvider. We’ll come back to the provider shortly.

You may also notice that it inherits something called PresentationContext. Let’s take a closer look at this base class.

Presentation context

Since I find that this problem is also true for sheets etc. I have a PresentationContext, which is a small ObservableObject base class with an isActive binding and a generic content view:

public class PresentationContext<Content>: ObservableObject {
    
    public init() {}
    
    @Published public var isActive = false
    
    public var isActiveBinding: Binding<Bool> {
        .init(get: { self.isActive },
              set: { self.isActive = $0 }
        )
    }
    
    open func content() -> Content { contentView! }
    
    public internal(set) var contentView: Content? {
        didSet { isActive = contentView != nil }
    }
    
    public func dismiss() {
        isActive = false
    }
    
    public func present(_ content: Content) {
        contentView = content
    }
}

By calling the alert-specific functions in AlertContext, the context state is properly updated.

Alert provider

As we saw earlier, AlertContext can present Alerts and AlertProviders. Alert is just a SwiftUI alert, while AlertProvider is a protocol for anything that can provide alerts:

public protocol AlertProvider {
    
    var alert: Alert { get }
}

For instance, you can have an enum that represents various alerts that your app supports:

enum AppAlert: AlertProvider {
    
    case test
    case warning(message: String)
    
    var alert: Alert {
        Alert(title: Text(message))
    }
}

private extension AppAlert {

    var message: String {
        switch self {
        case .test: return "This is a test alert"
        case .warning(let message): return message
        }
    }
}

Then present these alerts like this:

context.present(AppAlert.warning(message: "Something went wrong!"))

This makes it possible to create plain alerts or app- and view-specific enums and present all of them in the same way, using the same context.

New alert modifier

To present alert, your context must be added to a view. We can do this by wrapping the native alert modifier in a context-based modifier and provide it with the context state:

public extension View {
    
    func alert(_ context: AlertContext) -> some View {
        alert(isPresented: context.isActiveBinding, content: context.content)
    }
}

If you use this modifier instead of the native alert modifier, you can use the context to present alerts.

Presenting an alert

With these new tools at our disposal, we can present alerts in a much easier way.

First, create a context property:

@StateObject private var alert = AlertContext()

then add an alert modifier to the view:

.alert(alert)

You can now present any alerts or AlertProviders with the context:

// Present an alert
alert.present(Alert(message: "Hello, I'm a custom alert."))

// Present an alert provider
alert.present(AppAlert.test)

You no longer need multiple @State properties for different alerts or switch over an enum to determine which alert to show.

Conclusion

AlertContext can be used to present all different kind of alerts. It manages all state for you and lets you use a more convenient modifier. All you have to do is provide it with the alerts to present.

Source code

I have added these types to my SwiftUIKit library. You can find the source code here. Feel free to try it out and let me know what you think.