Runtime: Use attribute to find factory method.

Libs/GObject-2.0/Classes/ConstructAttribute.cs

@@ -0,0 +1,16 @@
+using System;
+
+namespace GObject
+{
+    /// <summary>
+    /// This attribute can be used to give the runtime
+    /// an alternative constructor method. This is
+    /// usefull if a constructor should return a
+    /// more derived type than the constructor itself.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Method)]
+    public class ConstructAttribute : Attribute
+    {
+
+    }
+}

Libs/GObject-2.0/Native/Classes/BoxedWrapper.cs

@@ -1,8 +1,6 @@
 using System;
-using System.Diagnostics;
+using System.Linq;
 using System.Reflection;
-using System.Runtime.InteropServices;
-using GLib;
 
 namespace GObject.Native
 {
@@ -44,13 +42,11 @@ public static object WrapHandle(IntPtr handle, Type gtype)
 
         private static MethodInfo? GetSecretFactoryMethod(System.Type type)
         {
-            // Create using 'IntPtr' constructor
-            MethodInfo? ctor = type.GetMethod("__FactoryNew",
-                System.Reflection.BindingFlags.NonPublic
-                | System.Reflection.BindingFlags.Static,
-                null, new[] { typeof(IntPtr) }, null
-            );
-            return ctor;
+            return type.GetMethods(
+                System.Reflection.BindingFlags.Static
+                | System.Reflection.BindingFlags.DeclaredOnly
+                | System.Reflection.BindingFlags.NonPublic
+            ).FirstOrDefault(x => x.GetCustomAttribute<ConstructAttribute>() is { });
         }
 
         private static ConstructorInfo? GetBoxedConstructor(System.Type type)

Libs/Gdk-3.0/Records/Event.cs

@@ -5,8 +5,9 @@ namespace Gdk
 {
     public partial class Event
     {
-        //TODO: This method is our "secret factory method". it gets called via reflection.
-        //See BoxedWrapper.cs
+        // TODO: Workaround as long as we need GDK3 or
+        // do not create instances from safe handles
+        [GObject.Construct]
         private static Event __FactoryNew(IntPtr ptr)
         {
             var ev = Marshal.PtrToStructure<Native.EventAny.Struct>(ptr);