496 words (approximately 3 mins)

Platform Lifecycle Events

Namespace: Microsoft.Maui.LifecycleEvents

  • .NET MAUI uses delegates that are invoked in response to a platform lifecycle event being raised.
  • You can create handlers for these delegates.

Android

Each delegate has an identically named extension method used to register a handler for that delegate.

Responding to Android Lifecycle Delegates

Call ConfigureLifecycleEvents method on MauiAppBuilder object in CreateMauiApp method of MauiProgram class:

using Microsoft.Maui.LifecycleEvents;

namespace PlatformLifecycleDemo 
{
    public static class MauiProgram 
    {
        public static MauiApp CreateMauiApp() 
        {
            var builder = MauiApp.CreateBuilder();
            builder
            .UseMauiApp<App>()
            .ConfigureLifecycleEvents(events => 
            {
                #if ANDROID
                events.AddAndroid(android => android
                .OnActivityResult((activity, requestCode, resultCode, data) => LogEvent("OnActivityResult", requestCode.ToString()))
                .OnStart((activity) => LogEvent("OnStart"))
                .OnCreate((activity, bundle) => LogEvent("OnCreate"))
                .OnBackPressed((activity) => LogEvent("OnBackPressed"))
                .OnStop((activity) => LogEvent("OnStop")));
                #endif

                static void LogEvent(string eventName, string type = null) 
                {
                    System.Diagnostics.Debug.WriteLine($"Lifecycle event: {eventName}{(type == null ? string.Empty : $" ({type})")}");
                }
            });

            return builder.Build();
        }
    }
}

iOS

Each delegate has an identically named extension method used to register a handler for that delegate.

Responding to iOS Lifecycle Delegates

Call ConfigureLifecycleEvents method on MauiAppBuilder object in CreateMauiApp method of MauiProgram class. Then on the ILifecycleBuilder object, call AddiOS method and specify the Action that registeres handlers for the required delegates:

using Microsoft.Maui.LifecycleEvents;

namespace PlatformLifecycleDemo 
{
    public static class MauiProgram 
    {
        public static MauiApp CreateMauiApp() 
        {
            var builder = MauiApp.CreateBuilder();
            builder
            .UseMauiApp<App>()
            .ConfigureLifecycleEvents(events => 
            {
                #if IOS
                events.AddiOS(ios => ios
                .OnActivated((app) => LogEvent("OnActivated"))
                .OnResignActivation((app) => LogEvent("OnResignActivation"))
                .DidEnterBackground((app) => LogEvent("DidEnterBackground"))
                .WillTerminate((app) => LogEvent("WillTerminate")));
                #endif
                static void LogEvent(string eventName, string type = null) 
                {
                    System.Diagnostics.Debug.WriteLine($"Lifecycle event: {eventName}{(type == null ? string.Empty : $" ({type})")}");
                }
            });

            return builder.Build();
        }
    }
}

Windows

.NET MAUI exposes some native Windows messages as a lifecycle event via the OnPlatformMessage delegate. This delegate includes the WindowsPlatformMessageEventArgs object, which includes a uint MessageId property.

Responding to Windows Lifecycle Delegates

Call ConfigureLifecycleEvents method on MauiAppBuilder object in CreateMauiApp method of MauiProgram class. Then on the ILifecycleBuilder object, call AddWindows method and specify the Action that registers handlers for the required delegates:

using Microsoft.Maui.LifecycleEvents;

namespace PlatformLifecycleDemo 
{
    public static class MauiProgram 
    {
        public static MauiApp CreateMauiApp() 
        {
            var builder = MauiApp.CreateBuilder();
            builder
            .UseMauiApp<App>()
            .ConfigureLifecycleEvents(events => 
            {
                #if WINDOWS
                events.AddWindows(windows => windows
                .OnActivated((window, args) => LogEvent("OnActivated"))
                .OnClosed((window, args) => LogEvent("OnClosed"))
                .OnLaunched((window, args) => LogEvent("OnLaunched"))
                .OnLaunching((window, args) => LogEvent("OnLaunching"))
                .OnVisibilityChanged((window, args) => LogEvent("OnVisibilityChanged"))
                .OnPlatformMessage((window, args) => 
                {
                    if (args.MessageId == Convert.ToUInt32("0x02E0")) 
                    {
                        // DPI has changed
                    }
                }));
                #endif
                
                static void LogEvent(string eventName, string type = null) 
                {
                    System.Diagnostics.Debug.WriteLine($"Lifecycle event: {eventName}{(type == null ? string.Empty : $" ({type})")}");
                }
            });

            return builder.Build();
        }
    }
}

Retrieving the Window Object

Platform code can retrieve the app’s Window object:

using Microsoft.Maui.LifecycleEvents;

namespace PlatformLifecycleDemo 
{
    public static class MauiProgram 
    {
        public static MauiApp CreateMauiApp() 
        {
            var builder = MauiApp.CreateBuilder();
            builder
            .UseMauiApp<App>()
            .ConfigureLifecycleEvents(events => 
            {
                #if WINDOWS
                events.AddWindows(windows => windows
                .OnClosed((window, args) => 
                {
                    IWindow appWindow = window.GetWindow();
                }));
                
                #endif
            });

            return builder.Build();
        }
    }
}