Keep a reference to gobject while signal is attached

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

@@ -210,6 +210,8 @@ namespace Avalonia.Gtk3.Interop
             [UnmanagedFunctionPointer(CallingConvention.Cdecl), GtkImport(GtkDll.Gobject)]
             public delegate void g_object_unref(IntPtr instance);
             [UnmanagedFunctionPointer(CallingConvention.Cdecl), GtkImport(GtkDll.Gobject)]
+            public delegate void g_object_ref(GObject instance);
+            [UnmanagedFunctionPointer(CallingConvention.Cdecl), GtkImport(GtkDll.Gobject)]
             public delegate ulong g_signal_connect_object(GObject instance, Utf8Buffer signal, IntPtr handler, IntPtr userData, int flags);
             [UnmanagedFunctionPointer(CallingConvention.Cdecl), GtkImport(GtkDll.Gobject)]
             public delegate ulong g_signal_handler_disconnect(GObject instance, ulong connectionId);
@@ -272,6 +274,7 @@ namespace Avalonia.Gtk3.Interop
         public static D.gtk_file_chooser_get_filenames GtkFileChooserGetFilenames;
         public static D.gtk_dialog_add_button GtkDialogAddButton;
         public static D.g_object_unref GObjectUnref;
+        public static D.g_object_ref GObjectRef;
         public static D.g_signal_connect_object GSignalConnectObject;
         public static D.g_signal_handler_disconnect GSignalHandlerDisconnect;
         public static D.g_timeout_add GTimeoutAdd;

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

@@ -18,6 +18,7 @@ namespace Avalonia.Gtk3.Interop
             public ConnectedSignal(GObject instance, GCHandle handle, ulong id)
             {
                 _instance = instance;
+                Native.GObjectRef(instance);
                 _handle = handle;
                 _id = id;
             }
@@ -26,6 +27,7 @@ namespace Avalonia.Gtk3.Interop
             {
                 if (_handle.IsAllocated)
                 {
+                    Native.GObjectUnref(_instance.DangerousGetHandle());
                     Native.GSignalHandlerDisconnect(_instance, _id);
                     _handle.Free();
                 }