Mac/iOS: register delegate protocols when the runtime doesn't know them

src/Avalonia.Controls.WebView.Core/Macios/Interop/AuthenticationServices/ASWebAuthenticationPresentationContextProviding.cs

@@ -17,13 +17,13 @@ static ASWebAuthenticationPresentationContextProviding()
 
         var delegateClass = AllocateClassPair("ManagedASWebAuthenticationPresentationContextProviding");
 
-        if (Libobjc.objc_getProtocol("ASWebAuthenticationPresentationContextProviding") is var protocol and > 0)
-        {
-            AddProtocol(delegateClass, protocol);   
-        }
+        var presentationAnchorSel = Libobjc.sel_getUid("presentationAnchorForWebAuthenticationSession:");
+
+        AddProtocol(delegateClass, "ASWebAuthenticationPresentationContextProviding",
+            new ProtocolMethod(presentationAnchorSel, "@@:@", true));
 
         AddMethod(delegateClass,
-            Libobjc.sel_getUid("presentationAnchorForWebAuthenticationSession:"),
+            presentationAnchorSel,
             new IntPtr(s_presentationAnchorForWebAuthenticationSession),
             "@@:@");
 

src/Avalonia.Controls.WebView.Core/Macios/Interop/Libobjc.cs

@@ -34,6 +34,14 @@ internal static unsafe partial class Libobjc
 
     [LibraryImport(libobjc, StringMarshalling = StringMarshalling.Utf8)]
     public static partial IntPtr objc_getProtocol(string selector);
+    [LibraryImport(libobjc, StringMarshalling = StringMarshalling.Utf8)]
+    public static partial IntPtr objc_allocateProtocol(string name);
+    [LibraryImport(libobjc)]
+    public static partial void objc_registerProtocol(IntPtr protocol);
+    [LibraryImport(libobjc)]
+    public static partial void protocol_addProtocol(IntPtr protocol, IntPtr addition);
+    [LibraryImport(libobjc, StringMarshalling = StringMarshalling.Utf8)]
+    public static partial void protocol_addMethodDescription(IntPtr protocol, IntPtr selector, string types, byte isRequiredMethod, byte isInstanceMethod);
     [LibraryImport(libobjc)]
     public static partial byte class_addProtocol(IntPtr basePtr, IntPtr protocol);
     [LibraryImport(libobjc, StringMarshalling = StringMarshalling.Utf8)]

src/Avalonia.Controls.WebView.Core/Macios/Interop/NSObject.cs

@@ -92,6 +92,51 @@ protected static void AddProtocol(IntPtr classHandle, IntPtr protocol)
         }
     }
 
+    /// <summary>
+    /// Adds the protocol to the class.
+    /// If the runtime doesn't know the protocol yet, registers one with the same name and the given methods.
+    /// </summary>
+    /// <remarks>
+    /// objc_getProtocol only finds protocols that some loaded image references.
+    /// On iOS 26, WebKit protocols are not always registered, and WebKit rejects handlers that don't conform.
+    /// The runtime checks conformance by protocol name, so a protocol with the same name is enough for conformsToProtocol:.
+    /// Method descriptions are still added, so code that inspects the protocol sees the same methods as in the original one.
+    /// </remarks>
+    protected static void AddProtocol(IntPtr classHandle, string protocolName, params ReadOnlySpan<ProtocolMethod> methods)
+    {
+        var protocol = Libobjc.objc_getProtocol(protocolName);
+        if (protocol == IntPtr.Zero)
+        {
+            protocol = Libobjc.objc_allocateProtocol(protocolName);
+            if (protocol == IntPtr.Zero)
+            {
+                // Another thread or image registered it in the meantime.
+                protocol = Libobjc.objc_getProtocol(protocolName);
+            }
+            else
+            {
+                if (Libobjc.objc_getProtocol("NSObject") is var nsObjectProtocol and not 0)
+                {
+                    Libobjc.protocol_addProtocol(protocol, nsObjectProtocol);
+                }
+                foreach (var method in methods)
+                {
+                    Libobjc.protocol_addMethodDescription(protocol, method.Selector, method.Types,
+                        method.Required ? (byte)1 : (byte)0, 1);
+                }
+                Libobjc.objc_registerProtocol(protocol);
+            }
+        }
+
+        if (protocol == IntPtr.Zero)
+        {
+            Logger.TryGet(LogEventLevel.Warning, "WebView")?.Log(null, "Failed to resolve {Protocol} protocol", protocolName);
+            return;
+        }
+
+        AddProtocol(classHandle, protocol);
+    }
+
     protected static void AddMethod(IntPtr classHandle, IntPtr selector, IntPtr methodHandler, string types)
     {
         if (classHandle == IntPtr.Zero)
@@ -266,6 +311,8 @@ protected internal unsafe IntPtr GetSuperRef()
         return new IntPtr(_superRef);
     }
 
+    protected readonly record struct ProtocolMethod(IntPtr Selector, string Types, bool Required);
+
     [StructLayout (LayoutKind.Sequential)]
     private struct ObjcSuper {
         public IntPtr Handle;

src/Avalonia.Controls.WebView.Core/Macios/Interop/WebKit/WKNavigationDelegate.cs

@@ -18,15 +18,16 @@ static WKNavigationDelegate()
     {
         var delegateClass = AllocateClassPair("ManagedWKNavigationDelegate");
 
-        if (Libobjc.objc_getProtocol("WKNavigationDelegate") is var protocol and > 0)
-        {
-            AddProtocol(delegateClass, protocol);   
-        }
-
         var willPresentNotificationSel = Libobjc.sel_getUid("webView:didFinishNavigation:");
+        var didReceiveNotificationResponse = Libobjc.sel_getUid("webView:decidePolicyForNavigationAction:decisionHandler:");
+
+        // All WKNavigationDelegate methods are optional.
+        AddProtocol(delegateClass, "WKNavigationDelegate",
+            new ProtocolMethod(willPresentNotificationSel, "v@:@@", false),
+            new ProtocolMethod(didReceiveNotificationResponse, "v@:@@@?", false));
+
         AddMethod(delegateClass, willPresentNotificationSel, new IntPtr(s_willPresentNotification), "v@:@@");
 
-        var didReceiveNotificationResponse = Libobjc.sel_getUid("webView:decidePolicyForNavigationAction:decisionHandler:");
         AddMethod(delegateClass, didReceiveNotificationResponse, new IntPtr(s_decidePolicyForNavigationAction), "v@:@@@");
 
         RegisterManagedMembers(delegateClass);

src/Avalonia.Controls.WebView.Core/Macios/Interop/WebKit/WKScriptMessageHandler.cs

@@ -19,13 +19,12 @@ static WKScriptMessageHandler()
     {
         var delegateClass = AllocateClassPair("ManagedWKScriptMessageHandler");
 
-        if (Libobjc.objc_getProtocol("WKScriptMessageHandler") is var protocol and > 0)
-        {
-            AddProtocol(delegateClass, protocol);   
-        }
+        var didReceiveScriptMessageSel = Libobjc.sel_getUid("userContentController:didReceiveScriptMessage:");
+
+        AddProtocol(delegateClass, "WKScriptMessageHandler",
+            new ProtocolMethod(didReceiveScriptMessageSel, "v@:@@", true));
 
-        var willPresentNotificationSel = Libobjc.sel_getUid("userContentController:didReceiveScriptMessage:");
-        AddMethod(delegateClass, willPresentNotificationSel, new IntPtr(s_didReceiveScriptMessage), "v@:@@");
+        AddMethod(delegateClass, didReceiveScriptMessageSel, new IntPtr(s_didReceiveScriptMessage), "v@:@@");
 
         RegisterManagedMembers(delegateClass);