feat: clean up code, allow empty host, simplify z index calculation.

demo/Ursa.Demo/Dialogs/DialogWithActionViewModel.cs

@@ -40,6 +40,6 @@ public partial class DialogWithActionViewModel: ObservableObject, IDialogContext
     
     private async Task ShowDialog()
     {
-        await DialogBox.ShowOverlayModalAsync<DialogWithAction, DialogWithActionViewModel, bool>(new DialogWithActionViewModel(), "GlobalHost");
+        await OverlayDialog.ShowModalAsync<DialogWithAction, DialogWithActionViewModel, bool>(new DialogWithActionViewModel());
     }
 }

demo/Ursa.Demo/ViewModels/DialogDemoViewModel.cs

@@ -45,25 +45,25 @@ public class DialogDemoViewModel: ObservableObject
 
     private void ShowGlobalOverlayDialog()
     {
-        DialogBox.ShowOverlay<DialogWithAction, DialogWithActionViewModel>(new DialogWithActionViewModel(), "GlobalHost");
+        OverlayDialog.Show<DialogWithAction, DialogWithActionViewModel>(new DialogWithActionViewModel());
     }
 
     private async Task ShowGlobalModalDialog()
     {
-        var result = await DialogBox.ShowModalAsync<DialogWithAction, DialogWithActionViewModel, bool>(DialogViewModel);
+        var result = await Dialog.ShowModalAsync<DialogWithAction, DialogWithActionViewModel, bool>(DialogViewModel);
         Result = result;
     }
 
     private async Task ShowGlobalOverlayModalDialog()
     {
-        Result = await DialogBox.ShowOverlayModalAsync<DialogWithAction, DialogWithActionViewModel, bool>(DialogViewModel, "GlobalHost");
+        Result = await OverlayDialog.ShowModalAsync<DialogWithAction, DialogWithActionViewModel, bool>(DialogViewModel);
     }
 
     private async Task ShowLocalOverlayModalDialog()
     {
         var vm = new DialogWithActionViewModel();
-        var result = await DialogBox.ShowOverlayModalAsync<DialogWithAction, DialogWithActionViewModel, bool>(
+        var result = await OverlayDialog.ShowModalAsync<DialogWithAction, DialogWithActionViewModel, bool>(
-            DialogViewModel, "LocalHost", new DialogOptions(){ ExtendToClientArea = true });
+            DialogViewModel, new DialogOptions() { ExtendToClientArea = true }, "LocalHost");
         Result = result;
     }
 }

demo/Ursa.Demo/Views/MainView.axaml

@@ -80,7 +80,7 @@
                 <converters:ViewLocator />
             </ContentControl.ContentTemplate>
         </ContentControl>
-        <u:OverlayDialogHost Grid.Row="0" Grid.Column="0" Grid.RowSpan="2" Grid.ColumnSpan="2" HostId="GlobalHost" />
+        <u:OverlayDialogHost Grid.Row="0" Grid.Column="0" Grid.RowSpan="2" Grid.ColumnSpan="2"/>
     </Grid>
 
 </UserControl>

src/Ursa/Controls/Dialog/Dialog.cs

@@ -6,39 +6,34 @@ using Avalonia.Media;
 
 namespace Ursa.Controls;
 
-public static class DialogBox
+public static class Dialog
 {
     public static async Task<TResult?> ShowModalAsync<TView, TViewModel, TResult>(TViewModel vm) 
         where TView : Control, new()
     {
-        var window = new DialogWindow()
+
-        {
-            Content = new TView(),
-            DataContext = vm,
-        };
         var lifetime = Application.Current?.ApplicationLifetime;
         if (lifetime is IClassicDesktopStyleApplicationLifetime classLifetime)
         {
-            var main = classLifetime.MainWindow;
+            var window = new DialogWindow
-            if (main is null)
+            {
+                Content = new TView { DataContext = vm },
+                DataContext = vm,
+            };
+            if (classLifetime.MainWindow is not { } main)
             {
                 window.Show();
-                return default(TResult);
+                return default;
-            }
-            else
-            {
-                var result = await window.ShowDialog<TResult>(main);
-                return result;
             }
+            var result = await window.ShowDialog<TResult>(main);
+            return result;
         }
-        else
+
-        {
+        return default(TResult);
-            return default(TResult);
-        }
     }
     
-    public static async Task<TResult> ShowModalAsync<TView, TViewModel, TResult>(Window owner, TViewModel vm) where 
+    public static async Task<TResult> ShowModalAsync<TView, TViewModel, TResult>(Window owner, TViewModel? vm) 
-        TView: Control, new()
+        where TView: Control, new()
     {
         var window = new DialogWindow
         {
@@ -47,9 +42,11 @@ public static class DialogBox
         };
         return await window.ShowDialog<TResult>(owner);
     }
-    
+}
 
-    public static Task<TResult> ShowOverlayModalAsync<TView, TViewModel, TResult>(TViewModel vm, string hostId)
+public static class OverlayDialog
+{
+    public static Task<TResult> ShowModalAsync<TView, TViewModel, TResult>(TViewModel vm, string? hostId = null)
         where TView : Control, new()
     {
         var t = new DialogControl()
@@ -62,8 +59,7 @@ public static class DialogBox
         return t.ShowAsync<TResult>();
     }
 
-    public static Task<TResult> ShowOverlayModalAsync<TView, TViewModel, TResult>(TViewModel vm, string hostId,
+    public static Task<TResult> ShowModalAsync<TView, TViewModel, TResult>(TViewModel vm, DialogOptions options, string? hostId = null)
-        DialogOptions options)
         where TView : Control, new()
     {
         var t = new DialogControl()
@@ -78,7 +74,7 @@ public static class DialogBox
         return t.ShowAsync<TResult>();
     }
 
-    public static void ShowOverlay<TView, TViewModel>(TViewModel vm, string hostId)
+    public static void Show<TView, TViewModel>(TViewModel vm, string? hostId = null)
         where TView: Control, new()
     {
         var t = new DialogControl()
@@ -90,7 +86,7 @@ public static class DialogBox
         host?.AddDialog(t);
     }
 
-    public static void ShowOverlay<TView, TViewModel>(TViewModel vm, string hostId, DialogOptions options)
+    public static void Show<TView, TViewModel>(TViewModel vm, DialogOptions options, string? hostId)
         where TView: Control, new()
     {
         var t = new DialogControl()

src/Ursa/Controls/Dialog/OverlayDialogHost.cs

@@ -1,13 +1,9 @@
-using System.Collections.Specialized;
 using Avalonia;
 using Avalonia.Controls;
-using Avalonia.Controls.Primitives;
-using Avalonia.Controls.Shapes;
 using Avalonia.Input;
 using Avalonia.Layout;
 using Avalonia.Media;
 using Avalonia.Utilities;
-using Avalonia.VisualTree;
 
 namespace Ursa.Controls;
 
@@ -53,7 +49,7 @@ public class OverlayDialogHost : Canvas
         for (int i = 0; i < _masks.Count; i++)
         {
             _masks[i].Width = this.Bounds.Width;
-            _masks[i].Width = this.Bounds.Height;
+            _masks[i].Height = this.Bounds.Height;
         }
     }
 
@@ -94,9 +90,9 @@ public class OverlayDialogHost : Canvas
     {
         this.Children.Add(control);
         _dialogs.Add(control);
-        control.ZIndex = Children.Last().ZIndex + 1;
         control.OnClose += OnDialogClose;
         control.OnLayerChange += OnDialogLayerChange;
+        ResetZIndices();
     }
 
     private void OnDialogClose(object sender, object? e)
@@ -124,32 +120,31 @@ public class OverlayDialogHost : Canvas
                     }
                 }
             }
+            ResetZIndices();
         }
     }
 
+    /// <summary>
+    ///  Add a dialog as a modal dialog to the host
+    /// </summary>
+    /// <param name="control"></param>
     internal void AddModalDialog(DialogControl control)
     {
         var mask = CreateOverlayMask();
         _masks.Add(mask);
         _modalDialogs.Add(control);
-        int start = _dialogs.LastOrDefault()?.ZIndex ?? 1;
-        for (int i = 0; i < _masks.Count; i += 1)
-        {
-            _masks[i].ZIndex = start + 2 * i;
-            _modalDialogs[i].ZIndex = start + 2 * i + 1;
-        }
-        
         for (int i = 0; i < _masks.Count-1; i++)
         {
             _masks[i].Opacity = 0.5;
         }
-
+        ResetZIndices();
         this.Children.Add(mask);
         this.Children.Add(control);
         control.OnClose += OnDialogClose;
         control.OnLayerChange += OnDialogLayerChange;
     }
 
+    // Handle dialog layer change event
     private void OnDialogLayerChange(object sender, DialogLayerChangeEventArgs e)
     {
         if (sender is not DialogControl control)
@@ -188,4 +183,21 @@ public class OverlayDialogHost : Canvas
         }
         
     }
+
+    private void ResetZIndices()
+    {
+        int index = 0;
+        for ( int i = 0; i< _dialogs.Count; i++)
+        {
+            _dialogs[i].ZIndex = index;
+            index++;
+        }
+        for(int i = 0; i< _masks.Count; i++)
+        {
+            _masks[i].ZIndex = index;
+            index++;
+            _modalDialogs[i].ZIndex = index;
+            index++;
+        }
+    }
 }

src/Ursa/Controls/Dialog/OverlayDialogManager.cs

@@ -4,20 +4,39 @@ namespace Ursa.Controls;
 
 internal static class OverlayDialogManager
 {
-    private static ConcurrentDictionary<string, OverlayDialogHost> _hosts = new();
+    private static OverlayDialogHost? _defaultHost;
+    private static readonly ConcurrentDictionary<string, OverlayDialogHost> Hosts = new();
     
-    public static void RegisterOverlayDialogHost(OverlayDialogHost host, string id)
+    public static void RegisterOverlayDialogHost(OverlayDialogHost host, string? id)
     {
-        _hosts.TryAdd(id, host);
+        if (id == null)
+        {
+            if (_defaultHost != null)
+            {
+                throw new InvalidOperationException("Cannot register multiple OverlayDialogHost with empty HostId");
+            }
+            _defaultHost = host;
+            return;
+        }
+        Hosts.TryAdd(id, host);
     }
     
-    public static void UnregisterOverlayDialogHost(string id)
+    public static void UnregisterOverlayDialogHost(string? id)
     {
-        _hosts.TryRemove(id, out _);
+        if (id is null)
+        {
+            _defaultHost = null;
+            return;
+        }
+        Hosts.TryRemove(id, out _);
     }
     
-    public static OverlayDialogHost? GetOverlayDialogHost(string id)
+    public static OverlayDialogHost? GetOverlayDialogHost(string? id)
     {
-        return _hosts.TryGetValue(id, out var host) ? host : null;
+        if (id is null)
+        {
+            return _defaultHost;
+        }
+        return Hosts.TryGetValue(id, out var host) ? host : null;
     }
 }