MAUI 9 handlers - how to access/override iOS platform lifecycle events?

[parmjitv]

Hello All,

I am currently porting an older Xamarin iOS application over to the MAUI 9 platform, and it is my understanding that the custom renderer feature in Xamarin has been deprecated in favour of the new handler approach in MAUI.

Presently, this application makes heavy use of Xamarin custom renderers to access key events in the iOS lifecycle:

• ViewWillDisappear
• ViewWillAppear
• ViewDidDisappear
• ViewDidAppear
• ViewDidLayoutSubviews

We attach specific low-level iOS code to these events for the various application screens. These events are readily accessible via Xamarin renders, but this accessibility appears to be missing with MAUI handlers. Nearly all handler documentation is in regard to extending the base MAUI controls for customization - Entry, DatePicker etc - but nothing regarding how to access and override the platform-specific lifecycle events.

So my question is two-fold:

1. Can we access the aforementioned iOS lifecycle events through a MAUI handler?

2. If not, what is the 'proper' approach in MAUI to access and override these events for iOS v18?

The application will be extended to also work for Android v16 in the near future, so I expect we will need a means to access the equivalent underlying lifecycle events for this platform as well.

This question may be somewhat related to the following issues:

#30
#10126
#14430
#25148

For completeness, I am using Visual Studio Code under MacOS Sequoia 15.5 with the .NET 9 framework and following workflows installed:

Installed Workload Id | Manifest Version | Installation Source
maui | 9.0.51/9.0.100 | SDK 9.0.300

Any guidance or code samples will be greatly appreciated. Thank you!

Cheers,

Parmjit V.

[PureWeen]

You can either

1. create a custom handler and then override "CreatePlatformView" to return a subclassed version of that platformview
2. use the static CreatePlatformViewFactory that's on each handler to accomplish the same thing

[parmjitv]

Thank you! Which approach would you recommend for my particular situation? Every content page/view in our original Xamarin iOS app is attached to a custom renderer, so I would assume the first approach is preferable?

[parmjitv]

Hello All,

It is possible to access the iOS lifecycle events through a MAUI handler. Credit to our friends over at Stack Overflow for the basic guide:

https://stackoverflow.com/questions/72632089/how-to-call-a-method-after-a-view-has-rendered-in-maui-onappearing-fires-too-s

Adjusted somewhat for my specific use-case, here is the implementation for a generic MAUI app called "MyMauiApp":

1. Under the "Platforms/iOS" folder, create a new directory "MyHandlers" and define a generic Page handler there:

using Microsoft.Maui.Handlers;
using Microsoft.Maui.Platform;
using UIKit;

namespace MyMauiApp.Platforms.iOS.MyHandlers;

// i.e. where type ContentPage is defined in your project
public class ContentPageHandler : PageHandler
{
	public class ContentPageController : PageViewController
	{
		private readonly ContentPage _contentPage;

		public ContentPageController(IView page, IMauiContext mauiContext) : base(page, mauiContext)
		{
			if (page is ContentPage)
			{
				_contentPage = page as ContentPage;
			}
		}

		// these iOS events fire for all pages of type ContentPage

		public override void ViewWillAppear(bool animated)
		{
			base.ViewWillAppear(animated);

			// do some custom stuff here
		}

		public override void ViewDidAppear(bool animated)
		{
			base.ViewDidAppear(animated);

			// do some custom stuff here
		}

		public override void ViewWillDisappear(bool animated)
		{
			base.ViewWillDisappear(animated);

			// do some custom stuff here
		}

		public override void ViewDidDisappear(bool animated)
		{
			base.ViewDidDisappear(animated);

			// do some custom stuff here
		}
	}

	protected override Microsoft.Maui.Platform.ContentView CreatePlatformView()
	{
		_ = VirtualView ?? throw new InvalidOperationException($"{nameof(VirtualView)} must be set to create a LayoutView");
		_ = MauiContext ?? throw new InvalidOperationException($"{nameof(MauiContext)} cannot be null");
		if (ViewController == null)
		{
			ViewController = new ContentPageController(VirtualView, MauiContext);
		}
		if (ViewController is PageViewController pc && pc.CurrentPlatformView is Microsoft.Maui.Platform.ContentView pv)
		{
			return pv;
		}
		if (ViewController.View is Microsoft.Maui.Platform.ContentView cv)
		{
			return cv;
		}
		throw new InvalidOperationException($"PageViewController.View must be a {nameof(Microsoft.Maui.Platform.ContentView)}");
	}
}

2. As with the previous Xamarin renderers, we can chain multiple handlers together via inheritance:

using Microsoft.Maui.Handlers;
using Microsoft.Maui.Platform;
using UIKit;

namespace MyMauiApp.Platforms.iOS.MyHandlers;

// i.e. where type MyPage is defined in your project
// inherits the custom iOS lifecycle event code from ContentPageHandler
public class MyPageHandler : ContentPageHandler
{
	public class MyPageController : ContentPageController
	{
		private readonly MyPage _myPage;

		public MyPageController(IView page, IMauiContext mauiContext) : base(page, mauiContext)
		{
			if (page is MyPage)
			{
				_myPage = page as MyPage;
			}
		}

		// iOS events ViewWillAppear, ViewDidAppear, ViewWillDisappear, ViewDidDisappear
		// all fire from ContentPageHandler
		
		// and this will fire for a page of type MyPage only
		public override void ViewDidLayoutSubviews()
		{
			base.ViewDidLayoutSubviews();

			// do some custom stuff here
		}
	}

	protected override Microsoft.Maui.Platform.ContentView CreatePlatformView()
	{
		_ = VirtualView ?? throw new InvalidOperationException($"{nameof(VirtualView)} must be set to create a LayoutView");
		_ = MauiContext ?? throw new InvalidOperationException($"{nameof(MauiContext)} cannot be null");
		if (ViewController == null)
		{
			ViewController = new MyPageController(VirtualView, MauiContext);
		}
		if (ViewController is PageViewController pc && pc.CurrentPlatformView is Microsoft.Maui.Platform.ContentView pv)
		{
			return pv;
		}
		if (ViewController.View is Microsoft.Maui.Platform.ContentView cv)
		{
			return cv;
		}
		throw new InvalidOperationException($"PageViewController.View must be a {nameof(Microsoft.Maui.Platform.ContentView)}");
	}
}

3. Finally, activate the respective handlers in the "MauiProgram.cs" file:

.ConfigureMauiHandlers(handlers =>
{
#if IOS
	handlers.AddHandler(typeof(ContentPage), typeof(Platforms.iOS.MyHandlers.ContentPageHandler));
	handlers.AddHandler(typeof(MyPage), typeof(Platforms.iOS.MyHandlers.MyPageHandler));
#endif
});

Hopefully this will help out a fellow MAUI traveller. I expect a similar approach can be used to intercept the lifecycle events for Android as well.

Happy coding,

Parmjit V.