No way to catch permissions requests from new .NET 9 HybridWebView? Old method doesn't work anymore.

[jonmdev]

Description

Instructions for catching and forwarding permissions request (eg. camera) in WebView are given here:

https://learn.microsoft.com/en-us/dotnet/maui/user-interface/controls/webview?view=net-maui-8.0&pivots=devices-android

HybridWebView used to derive from it (not sure now) so it worked the same way.

They suggest creating a MyWebChromeClient and then setting this on the platform view of the WebView in Android:

var webViewHandler = (IWebViewHandler)webView.Handler;
var chromeClient = new MauiAppWebViewHandlers.Platforms.Android.MyWebChromeClient(webViewHandler);
webViewHandler.PlatformView.SetWebChromeClient(chromeClient);

However, if you try this, it does not work in .NET Maui with HybridWebView. It previously worked fine in .NET 8. Now you are told:

**System.InvalidCastException:** 'Specified cast is not valid.'

Regarding conversion of the webView handler to IWebViewHandler. Thus we cannot create the MyWebChromeClient according to these directions.

What might be the fix? @Eilon, I know this is your baby. Any thoughts or solution? Thanks.

Steps to Reproduce

Run the demo project in Android and see the error that returns.

Demo project was made by just two things: (1) Copy and paste the demo MyWebChromeClient code into ChromeClient.cs, and (2) Copy and paste the following in to App.xaml.cs:

        protected override Window CreateWindow(IActivationState? activationState)
        {
            ContentPage mainPage = new();
            HybridWebView webView = new();
            mainPage.Content = webView;
#if ANDROID

            webView.HandlerChanged += delegate {

                var platformView = webView.ToPlatform(webView.Handler.MauiContext);
                Debug.WriteLine("PLATFORM VIEW " + platformView.GetType());//Microsoft.Maui.Platform.MauiHybridWebView
                Debug.WriteLine("HANDLER PLATFORM VIEW " + webView.Handler.PlatformView.GetType()); //Microsoft.Maui.Platform.MauiHybridWebView
                Debug.WriteLine("HANDLER " + webView.Handler.GetType());//Microsoft.Maui.Handlers.HybridWebViewHandler
                var webViewHandler = (IWebViewHandler)webView.Handler;
                Debug.Assert(webViewHandler != null, "Value must not be null.");
                var chromeClient = new MauiAppWebViewHandlers.Platforms.Android.MyWebChromeClient(webViewHandler);
                webViewHandler.PlatformView.SetWebChromeClient(chromeClient);
            };


#endif
            return new Window(mainPage);
        }

Link to public reproduction project repository

https://github.com/jonmdev/HybridWebViewPermissionsBug

Version with bug

9.0.0-rc.1.24453.9

Is this a regression from previous behavior?

Yes, this used to work in .NET MAUI

Last version that worked well

8.0.0-preview.1.7762

Affected platforms

Android

Affected platform versions

No response

Did you find any workaround?

None

Relevant log output

**System.InvalidCastException:** 'Specified cast is not valid.'

[jaosnz-rep]

I can repro System.InvalidCastException at Android platform on the latest 17.13.0 Preview 1.0(9.0.0-rc.1.24453.9). Unfortunately, I can't verify on .NET8 due to CS0246 error(The type or namespace name 'HybridWebView' could not be found). If you have any questions, please feel free to contact me.

[jonmdev]

I need this fixed so I looked more.

The problem is that the constructor for MauiWebChromeClient requires an IWebViewHandler which HybridWebView doesn't have.

This is here:

maui/src/Core/src/Platform/Android/MauiWebChromeClient.cs

Line 12 in 07f41ae

public class MauiWebChromeClient : WebChromeClient

		public MauiWebChromeClient(IWebViewHandler handler)
		{
			_ = handler ?? throw new ArgumentNullException(nameof(handler));

			SetContext(handler);
		}

This is not necessary to be so specific about the argument it takes. All it is doing with this handler is getting the Android.App.Activity with SetContext where it then stores a weak reference to the Android Activity.

Thus the simplest solutions would be to (1) Add another constructor that takes a HybridWebViewHandler with the same content, or (2) Relax the type of argument MauiWebChromeClient takes so it will be compatible with both (like IViewHandler).

My workaround is as follows:

1) Create MyWebChromeClient as instructed usually but with extra new constructor

internal class MyWebChromeClient : MauiWebChromeClient {
    //=========================================================================================
    // CUSTOM FIX FOR PERMISSIONS ISSUE https://github.com/dotnet/maui/issues/25784
    //=========================================================================================
    public MyWebChromeClient(IWebViewHandler fakeHandler, HybridWebViewHandler realHandler) : base(fakeHandler) {
        //base constructor (base(fakeHandler)) is automatically called before customSetContext(realHandler) 
        customSetContext(realHandler);
    }
    public void customSetContext(HybridWebViewHandler handler) {
        //copied and pasted from https://github.com/dotnet/maui/blob/07f41ae8209b9f00e784dacb87d70860622ff4e9/src/Core/src/Platform/Android/MauiWebChromeClient.cs#L12
        var activity = handler?.MauiContext?.Context?.GetActivity();

        if (activity == null) {
            Debug.WriteLine("FAILED TO GET ACTIVITY");
            //handler?.MauiContext?.CreateLogger<WebViewHandler>()?.LogWarning($"Failed to set the activity of the WebChromeClient, can't show pickers on the Webview");
        }

        // Use reflection to access the private _activityRef field in the base class
        var fieldInfo = typeof(MauiWebChromeClient).GetField("_activityRef", BindingFlags.NonPublic | BindingFlags.Instance);

        if (fieldInfo != null) {
            // Create a new WeakReference<Activity> to wrap the provided activity
            var activityWeakRef = new WeakReference<Android.App.Activity>(activity);

            // Set the value of _activityRef using reflection
            fieldInfo.SetValue(this, activityWeakRef);
        }
        else {
            Debug.WriteLine("FAILED TO GET _ACTIVITYREF BY REFLECTION");
        }
        //_activityRef = new WeakReference<Activity>(activity); //can't set as not public

    }
    //=========================================================================================
    public MyWebChromeClient(IWebViewHandler handler) : base(handler) {
        
    }
    public override void OnPermissionRequest(PermissionRequest request) {
    }
}

2) Use this new constructor to build the ChromeClient

            HybridWebView webView = new();
            mainPage.Content = webView;
#if ANDROID

            webView.HandlerChanged += delegate {
                var platformView = webView.ToPlatform(webView.Handler.MauiContext);
                IWebViewHandler fakeHandler = new WebViewHandler(); // make fake handler to satisfy base WebChromeClient constructor
                HybridWebViewHandler realHandler = webView.Handler as HybridWebViewHandler;
                
                var chromeClient = new MyWebChromeClient(fakeHandler, realHandler);
                realHandler.PlatformView.SetWebChromeClient(chromeClient); 
            };
#endif

I have tested this and it seems to work. I updated the bug project with the "fix."

Extra issue

I note also for some reason platformView.SetWebChromeClient(null); was commented out of HybridWebViewHandler.Android.cs but it is still present in WebViewHandler.Android.cs.

I assume this is to prevent some memory leak and it should be present in both:

• maui/src/Core/src/Handlers/WebView/WebViewHandler.Android.cs

  Line 62 in 07f41ae

  platformView.SetWebChromeClient(null);

• maui/src/Core/src/Handlers/HybridWebView/HybridWebViewHandler.Android.cs

  Line 84 in 07f41ae

  //platformView.SetWebChromeClient(null);