Added GTK support for common dialogs

src/Gtk/Perspex.Gtk/CommonDialogImpl.cs

@@ -0,0 +1,57 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Perspex.Controls;
+using Perspex.Controls.Platform;
+using Perspex.Platform;
+
+namespace Perspex.Gtk
+{
+    using global::Gtk;
+    class CommonDialogImpl : ICommonDialogImpl
+    {
+        public Task<string[]> ShowAsync(CommonDialog dialog, IWindowImpl parent)
+        {
+            var tcs = new TaskCompletionSource<string[]>();
+            var dlg = new global::Gtk.FileChooserDialog(dialog.Title, ((WindowImpl) parent),
+                dialog.Action == CommonDialogAction.OpenFile
+                    ? FileChooserAction.Open
+                    : FileChooserAction.Save,
+                "Cancel", ResponseType.Cancel,
+                "Open", ResponseType.Accept)
+            {
+                SelectMultiple = dialog.AllowMultiple,
+            };
+            foreach (var filter in dialog.Filters)
+            {
+                var ffilter = new FileFilter()
+                {
+                    Name = filter.Name + " (" + string.Join(";", filter.Extensions.Select(e => "*." + e)) + ")"
+                };
+                foreach (var ext in filter.Extensions)
+                    ffilter.AddPattern("*." + ext);
+                dlg.AddFilter(ffilter);
+            }
+            dlg.SetFilename(dialog.InitialFileName);
+            dlg.Modal = true;
+
+            dlg.Response += (_, args) =>
+            {
+                if (args.ResponseId == ResponseType.Accept)
+                    tcs.TrySetResult(dlg.Filenames);
+                dlg.Hide();
+                dlg.Dispose();
+            };
+            
+            dlg.Close += delegate
+            {
+                tcs.TrySetResult(null);
+                dlg.Dispose();
+            };
+            dlg.Show();
+            return tcs.Task;
+        }
+    }
+}

src/Gtk/Perspex.Gtk/GtkPlatform.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Reactive.Disposables;
+using Perspex.Controls.Platform;
 using Perspex.Input.Platform;
 using Perspex.Input;
 using Perspex.Platform;
@@ -36,6 +37,7 @@ namespace Perspex.Gtk
             locator.Register(() => GtkKeyboardDevice.Instance, typeof(IKeyboardDevice));
             locator.Register(() => s_instance, typeof(IPlatformSettings));
             locator.Register(() => s_instance, typeof(IPlatformThreadingInterface));
+            locator.Register(() => new CommonDialogImpl(), typeof (ICommonDialogImpl));
             SharedPlatform.Register();
         }
 

src/Gtk/Perspex.Gtk/Perspex.Gtk.csproj

@@ -50,6 +50,7 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="ClipboardImpl.cs" />
+    <Compile Include="CommonDialogImpl.cs" />
     <Compile Include="CursorFactory.cs" />
     <Compile Include="GtkExtensions.cs" />
     <Compile Include="PopupImpl.cs" />