Mono support

src/Gtk/Avalonia.Gtk3/Gtk3Platform.cs

@@ -24,7 +24,8 @@ namespace Avalonia.Gtk3
         {
             Resolver.Resolve();
             Native.GtkInit(0, IntPtr.Zero);
-            App = Native.GtkApplicationNew("avalonia.app." + Guid.NewGuid(), 0);
+            using (var utf = new Utf8Buffer("avalonia.app." + Guid.NewGuid()))
+                App = Native.GtkApplicationNew(utf, 0);
             //Mark current thread as UI thread
             s_tlsMarker = true;
 

src/Gtk/Avalonia.Gtk3/Interop/Native.cs

@@ -20,7 +20,7 @@ namespace Avalonia.Gtk3.Interop
         public static class D
         {
             [UnmanagedFunctionPointer(CallingConvention.Cdecl), GtkImport(GtkDll.Gtk)]
-            public delegate IntPtr gtk_application_new([MarshalAs(UnmanagedType.AnsiBStr)] string appId, int flags);
+            public delegate IntPtr gtk_application_new(Utf8Buffer appId, int flags);
 
             [UnmanagedFunctionPointer(CallingConvention.Cdecl), GtkImport(GtkDll.Gtk)]
             public delegate void gtk_main_iteration();
@@ -113,7 +113,7 @@ namespace Avalonia.Gtk3.Interop
             [UnmanagedFunctionPointer(CallingConvention.Cdecl), GtkImport(GtkDll.Gdk)]
             public delegate void gdk_window_invalidate_rect(IntPtr window, ref GdkRectangle rect, bool invalidate_children);
             [UnmanagedFunctionPointer(CallingConvention.Cdecl), GtkImport(GtkDll.Gobject)]
-            public delegate ulong g_signal_connect_object(IntPtr instance, [MarshalAs(UnmanagedType.AnsiBStr)]string signal, IntPtr handler, IntPtr userData, int flags);
+            public delegate ulong g_signal_connect_object(IntPtr instance, Utf8Buffer signal, IntPtr handler, IntPtr userData, int flags);
             [UnmanagedFunctionPointer(CallingConvention.Cdecl), GtkImport(GtkDll.Gobject)]
             public delegate ulong g_signal_handler_disconnect(IntPtr instance, ulong connectionId);
             [UnmanagedFunctionPointer(CallingConvention.Cdecl), GtkImport(GtkDll.Glib)]

src/Gtk/Avalonia.Gtk3/Interop/Signal.cs

@@ -36,10 +36,13 @@ namespace Avalonia.Gtk3.Interop
         {
             var handle = GCHandle.Alloc(handler);
             var ptr = Marshal.GetFunctionPointerForDelegate((Delegate)(object)handler);
-            var id = Native.GSignalConnectObject(obj, name, ptr, IntPtr.Zero, 0);
-            if (id == 0)
-                throw new ArgumentException("Unable to connect to signal " + name);
-            return new ConnectedSignal(obj, handle, id);
+            using (var utf = new Utf8Buffer(name))
+            {
+                var id = Native.GSignalConnectObject(obj, utf, ptr, IntPtr.Zero, 0);
+                if (id == 0)
+                    throw new ArgumentException("Unable to connect to signal " + name);
+                return new ConnectedSignal(obj, handle, id);
+            }
         }
     }
 }