Remove Window.ShowDialog variant that takes IWindowImpl.

src/Avalonia.Controls/Platform/ISystemDialogImpl.cs

@@ -1,5 +1,4 @@
 using System.Threading.Tasks;
-using Avalonia.Platform;
 
 namespace Avalonia.Controls.Platform
 {
@@ -14,8 +13,8 @@ namespace Avalonia.Controls.Platform
         /// <param name="dialog">The details of the file dialog to show.</param>
         /// <param name="parent">The parent window.</param>
         /// <returns>A task returning the selected filenames.</returns>
-        Task<string[]> ShowFileDialogAsync(FileDialog dialog, IWindowImpl parent);
+        Task<string[]> ShowFileDialogAsync(FileDialog dialog, Window parent);
 
-        Task<string> ShowFolderDialogAsync(OpenFolderDialog dialog, IWindowImpl parent);   
+        Task<string> ShowFolderDialogAsync(OpenFolderDialog dialog, Window parent);
     }
 }

src/Avalonia.Controls/SystemDialog.cs

@@ -32,7 +32,7 @@ namespace Avalonia.Controls
             if(parent == null)
                 throw new ArgumentNullException(nameof(parent));
             return ((await AvaloniaLocator.Current.GetService<ISystemDialogImpl>()
-                 .ShowFileDialogAsync(this, parent?.PlatformImpl)) ??
+                 .ShowFileDialogAsync(this, parent)) ??
              Array.Empty<string>()).FirstOrDefault();
         }
     }
@@ -45,7 +45,7 @@ namespace Avalonia.Controls
         {
             if(parent == null)
                 throw new ArgumentNullException(nameof(parent));
-            return AvaloniaLocator.Current.GetService<ISystemDialogImpl>().ShowFileDialogAsync(this, parent?.PlatformImpl);
+            return AvaloniaLocator.Current.GetService<ISystemDialogImpl>().ShowFileDialogAsync(this, parent);
         }
     }
 
@@ -61,7 +61,7 @@ namespace Avalonia.Controls
         {
             if(parent == null)
                 throw new ArgumentNullException(nameof(parent));
-            return AvaloniaLocator.Current.GetService<ISystemDialogImpl>().ShowFolderDialogAsync(this, parent?.PlatformImpl);
+            return AvaloniaLocator.Current.GetService<ISystemDialogImpl>().ShowFolderDialogAsync(this, parent);
         }
     }
 

src/Avalonia.Controls/Window.cs

@@ -484,22 +484,12 @@ namespace Avalonia.Controls
         /// <returns>.
         /// A task that can be used to retrieve the result of the dialog when it closes.
         /// </returns>
-        public Task<TResult> ShowDialog<TResult>(Window owner) => ShowDialog<TResult>(owner.PlatformImpl);
-
-        /// <summary>
-        /// Shows the window as a dialog.
-        /// </summary>
-        /// <typeparam name="TResult">
-        /// The type of the result produced by the dialog.
-        /// </typeparam>
-        /// <param name="owner">The dialog's owner window.</param>
-        /// <returns>.
-        /// A task that can be used to retrieve the result of the dialog when it closes.
-        /// </returns>
-        public Task<TResult> ShowDialog<TResult>(IWindowImpl owner)
+        public Task<TResult> ShowDialog<TResult>(Window owner)
         {
             if (owner == null)
+            {
                 throw new ArgumentNullException(nameof(owner));
+            }
 
             if (IsVisible)
             {
@@ -516,23 +506,25 @@ namespace Avalonia.Controls
 
             using (BeginAutoSizing())
             {
-
-                PlatformImpl?.ShowDialog(owner);
+                PlatformImpl?.ShowDialog(owner.PlatformImpl);
 
                 Renderer?.Start();
+
                 Observable.FromEventPattern<EventHandler, EventArgs>(
-                    x => this.Closed += x,
-                    x => this.Closed -= x)
+                        x => Closed += x,
+                        x => Closed -= x)
                     .Take(1)
                     .Subscribe(_ =>
                     {
                         owner.Activate();
                         result.SetResult((TResult)(_dialogResult ?? default(TResult)));
                     });
+
                 OnOpened(EventArgs.Empty);
             }
 
-            SetWindowStartupLocation(owner);
+            SetWindowStartupLocation(owner.PlatformImpl);
+
             return result.Task;
         }
 

src/Avalonia.DesignerSupport/Remote/Stubs.cs

@@ -166,10 +166,10 @@ namespace Avalonia.DesignerSupport.Remote
 
     class SystemDialogsStub : ISystemDialogImpl
     {
-        public Task<string[]> ShowFileDialogAsync(FileDialog dialog, IWindowImpl parent) =>
+        public Task<string[]> ShowFileDialogAsync(FileDialog dialog, Window parent) =>
             Task.FromResult((string[])null);
 
-        public Task<string> ShowFolderDialogAsync(OpenFolderDialog dialog, IWindowImpl parent) =>
+        public Task<string> ShowFolderDialogAsync(OpenFolderDialog dialog, Window parent) =>
             Task.FromResult((string)null);
     }
 

src/Avalonia.Dialogs/ManagedFileDialogExtensions.cs

@@ -1,19 +1,15 @@
-using System;
 using System.Linq;
 using System.Threading.Tasks;
-using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Controls.Platform;
-using Avalonia.Dialogs;
-using Avalonia.Platform;
 
 namespace Avalonia.Dialogs
 {
     public static class ManagedFileDialogExtensions
     {
-        class ManagedSystemDialogImpl<T> : ISystemDialogImpl where T : Window, new()
+        private class ManagedSystemDialogImpl<T> : ISystemDialogImpl where T : Window, new()
         {
-            async Task<string[]> Show(SystemDialog d, IWindowImpl parent)
+            async Task<string[]> Show(SystemDialog d, Window parent)
             {
                 var model = new ManagedFileChooserViewModel((FileSystemDialog)d);
 
@@ -39,12 +35,12 @@ namespace Avalonia.Dialogs
                 return result;
             }
 
-            public async Task<string[]> ShowFileDialogAsync(FileDialog dialog, IWindowImpl parent)
+            public async Task<string[]> ShowFileDialogAsync(FileDialog dialog, Window parent)
             {
                 return await Show(dialog, parent);
             }
 
-            public async Task<string> ShowFolderDialogAsync(OpenFolderDialog dialog, IWindowImpl parent)
+            public async Task<string> ShowFolderDialogAsync(OpenFolderDialog dialog, Window parent)
             {
                 return (await Show(dialog, parent))?.FirstOrDefault();
             }

src/Avalonia.Native/SystemDialogs.cs

@@ -5,7 +5,6 @@ using System.Threading.Tasks;
 using Avalonia.Controls;
 using Avalonia.Controls.Platform;
 using Avalonia.Native.Interop;
-using Avalonia.Platform;
 
 namespace Avalonia.Native
 {
@@ -18,13 +17,15 @@ namespace Avalonia.Native
             _native = native;
         }
 
-        public Task<string[]> ShowFileDialogAsync(FileDialog dialog, IWindowImpl parent)
+        public Task<string[]> ShowFileDialogAsync(FileDialog dialog, Window parent)
         {
             var events = new SystemDialogEvents();
 
+            var nativeParent = GetNativeWindow(parent);
+
             if (dialog is OpenFileDialog ofd)
             {
-                _native.OpenFileDialog((parent as WindowImpl)?.Native,
+                _native.OpenFileDialog(nativeParent,
                                         events, ofd.AllowMultiple,
                                         ofd.Title ?? "",
                                         ofd.InitialDirectory ?? "",
@@ -33,7 +34,7 @@ namespace Avalonia.Native
             }
             else
             {
-                _native.SaveFileDialog((parent as WindowImpl)?.Native,
+                _native.SaveFileDialog(nativeParent,
                                         events,
                                         dialog.Title ?? "",
                                         dialog.InitialDirectory ?? "",
@@ -44,14 +45,21 @@ namespace Avalonia.Native
             return events.Task.ContinueWith(t => { events.Dispose(); return t.Result; });
         }
 
-        public Task<string> ShowFolderDialogAsync(OpenFolderDialog dialog, IWindowImpl parent)
+        public Task<string> ShowFolderDialogAsync(OpenFolderDialog dialog, Window parent)
         {
             var events = new SystemDialogEvents();
 
-            _native.SelectFolderDialog((parent as WindowImpl)?.Native, events, dialog.Title ?? "", dialog.InitialDirectory ?? "");
+            var nativeParent = GetNativeWindow(parent);
+
+            _native.SelectFolderDialog(nativeParent, events, dialog.Title ?? "", dialog.InitialDirectory ?? "");
 
             return events.Task.ContinueWith(t => { events.Dispose(); return t.Result.FirstOrDefault(); });
         }
+
+        private IAvnWindow GetNativeWindow(Window window)
+        {
+            return (window?.PlatformImpl as WindowImpl)?.Native;
+        }
     }
 
     public class SystemDialogEvents : CallbackBase, IAvnSystemDialogEvents

src/Avalonia.X11/NativeDialogs/GtkNativeFileDialogs.cs

@@ -102,23 +102,23 @@ namespace Avalonia.X11.NativeDialogs
             return tcs.Task;
         }
         
-        public async Task<string[]> ShowFileDialogAsync(FileDialog dialog, IWindowImpl parent)
+        public async Task<string[]> ShowFileDialogAsync(FileDialog dialog, Window parent)
         {
             await EnsureInitialized();
             return await await RunOnGlibThread(
-                () => ShowDialog(dialog.Title, parent,
+                () => ShowDialog(dialog.Title, parent?.PlatformImpl,
                     dialog is OpenFileDialog ? GtkFileChooserAction.Open : GtkFileChooserAction.Save,
                     (dialog as OpenFileDialog)?.AllowMultiple ?? false,
                     Path.Combine(string.IsNullOrEmpty(dialog.InitialDirectory) ? "" : dialog.InitialDirectory,
                         string.IsNullOrEmpty(dialog.InitialFileName) ? "" : dialog.InitialFileName), dialog.Filters));
         }
 
-        public async Task<string> ShowFolderDialogAsync(OpenFolderDialog dialog, IWindowImpl parent)
+        public async Task<string> ShowFolderDialogAsync(OpenFolderDialog dialog, Window parent)
         {
             await EnsureInitialized();
             return await await RunOnGlibThread(async () =>
             {
-                var res = await ShowDialog(dialog.Title, parent,
+                var res = await ShowDialog(dialog.Title, parent?.PlatformImpl,
                     GtkFileChooserAction.SelectFolder, false, dialog.InitialDirectory, null);
                 return res?.FirstOrDefault();
             });

src/Windows/Avalonia.Win32/SystemDialogImpl.cs

@@ -5,7 +5,6 @@ using System.Runtime.InteropServices;
 using System.Threading.Tasks;
 using Avalonia.Controls;
 using Avalonia.Controls.Platform;
-using Avalonia.Platform;
 using Avalonia.Win32.Interop;
 
 namespace Avalonia.Win32
@@ -16,9 +15,9 @@ namespace Avalonia.Win32
         private const UnmanagedMethods.FOS DefaultDialogOptions = UnmanagedMethods.FOS.FOS_FORCEFILESYSTEM | UnmanagedMethods.FOS.FOS_NOVALIDATE |
             UnmanagedMethods.FOS.FOS_NOTESTFILECREATE | UnmanagedMethods.FOS.FOS_DONTADDTORECENT;
 
-        public unsafe Task<string[]> ShowFileDialogAsync(FileDialog dialog, IWindowImpl parent)
+        public unsafe Task<string[]> ShowFileDialogAsync(FileDialog dialog, Window parent)
         {
-            var hWnd = parent?.Handle?.Handle ?? IntPtr.Zero;
+            var hWnd = parent?.PlatformImpl?.Handle?.Handle ?? IntPtr.Zero;
             return Task.Factory.StartNew(() =>
             {
                 var result = Array.Empty<string>();
@@ -98,13 +97,13 @@ namespace Avalonia.Win32
             });
         }
 
-        public Task<string> ShowFolderDialogAsync(OpenFolderDialog dialog, IWindowImpl parent)
+        public Task<string> ShowFolderDialogAsync(OpenFolderDialog dialog, Window parent)
         {
             return Task.Factory.StartNew(() =>
             {
                 string result = string.Empty;
 
-                var hWnd = parent?.Handle?.Handle ?? IntPtr.Zero;
+                var hWnd = parent?.PlatformImpl?.Handle?.Handle ?? IntPtr.Zero;
                 Guid clsid = UnmanagedMethods.ShellIds.OpenFileDialog;
                 Guid iid  = UnmanagedMethods.ShellIds.IFileDialog;
 

tests/Avalonia.Controls.UnitTests/WindowTests.cs

@@ -156,7 +156,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var parent = Mock.Of<IWindowImpl>();
+                var parent = Mock.Of<Window>();
                 var renderer = new Mock<IRenderer>();
                 var target = new Window(CreateImpl(renderer));
 
@@ -171,7 +171,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var parent = Mock.Of<IWindowImpl>();
+                var parent = Mock.Of<Window>();
                 var target = new Window();
                 var raised = false;
 
@@ -203,7 +203,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var parent = new Mock<IWindowImpl>();
+                var parent = new Mock<Window>();
                 var windowImpl = new Mock<IWindowImpl>();
                 windowImpl.SetupProperty(x => x.Closed);
                 windowImpl.Setup(x => x.Scaling).Returns(1);
@@ -242,7 +242,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var parent = new Mock<IWindowImpl>();
+                var parent = new Mock<Window>();
                 var windowImpl = new Mock<IWindowImpl>();
                 windowImpl.SetupProperty(x => x.Closed);
                 windowImpl.Setup(x => x.Scaling).Returns(1);