feat: simplify name, set to center by default.

demo/Ursa.Demo/Pages/DialogDemo.axaml

@@ -33,7 +33,9 @@
                 Command="{Binding ShowLocalOverlayModalDialogCommand}">
                 Show Local Overlay Dialog
             </Button>
+            <Border CornerRadius="20" ClipToBounds="True">
                 <u:OverlayDialogHost HostId="LocalHost" />
+            </Border>
         </Grid>
     </Grid>
 </UserControl>

src/Ursa/Controls/Dialog/Dialog.cs

@@ -54,7 +54,7 @@ public static class OverlayDialog
             Content = new TView(){ DataContext = vm },
             DataContext = vm,
         };
-        var host = OverlayDialogManager.GetOverlayDialogHost(hostId);
+        var host = OverlayDialogManager.GetHost(hostId);
         host?.AddModalDialog(t);
         return t.ShowAsync<TResult>();
     }
@@ -69,7 +69,7 @@ public static class OverlayDialog
             ExtendToClientArea = options.ExtendToClientArea,
             Title = options.Title,
         };
-        var host = OverlayDialogManager.GetOverlayDialogHost(hostId);
+        var host = OverlayDialogManager.GetHost(hostId);
         host?.AddModalDialog(t);
         return t.ShowAsync<TResult>();
     }
@@ -82,7 +82,7 @@ public static class OverlayDialog
             Content = new TView() { DataContext = vm },
             DataContext = vm,
         };
-        var host = OverlayDialogManager.GetOverlayDialogHost(hostId);
+        var host = OverlayDialogManager.GetHost(hostId);
         host?.AddDialog(t);
     }
 
@@ -96,7 +96,7 @@ public static class OverlayDialog
             ExtendToClientArea = options.ExtendToClientArea,
             Title = options.Title,
         };
-        var host = OverlayDialogManager.GetOverlayDialogHost(hostId);
+        var host = OverlayDialogManager.GetHost(hostId);
         host?.AddModalDialog(t);
     }
 }

src/Ursa/Controls/Dialog/OverlayDialogHost.cs

@@ -1,5 +1,6 @@
 using Avalonia;
 using Avalonia.Controls;
+using Avalonia.Controls.Primitives;
 using Avalonia.Input;
 using Avalonia.Layout;
 using Avalonia.Media;
@@ -40,7 +41,7 @@ public class OverlayDialogHost : Canvas
     protected sealed override void OnAttachedToVisualTree(VisualTreeAttachmentEventArgs e)
     {
         base.OnAttachedToVisualTree(e);
-        OverlayDialogManager.RegisterOverlayDialogHost(this, HostId);
+        OverlayDialogManager.RegisterHost(this, HostId);
     }
 
     protected sealed override void OnSizeChanged(SizeChangedEventArgs e)
@@ -55,7 +56,7 @@ public class OverlayDialogHost : Canvas
 
     protected override void OnDetachedFromVisualTree(VisualTreeAttachmentEventArgs e)
     {
-        OverlayDialogManager.UnregisterOverlayDialogHost(HostId);
+        OverlayDialogManager.UnregisterHost(HostId);
         base.OnDetachedFromVisualTree(e);
     }
 
@@ -90,6 +91,9 @@ public class OverlayDialogHost : Canvas
     {
         this.Children.Add(control);
         _dialogs.Add(control);
+        control.Measure(this.Bounds.Size);
+        control.Arrange(new Rect(control.DesiredSize));
+        SetToCenter(control);
         control.OnClose += OnDialogClose;
         control.OnLayerChange += OnDialogLayerChange;
         ResetZIndices();
@@ -140,6 +144,9 @@ public class OverlayDialogHost : Canvas
         ResetZIndices();
         this.Children.Add(mask);
         this.Children.Add(control);
+        control.Measure(this.Bounds.Size);
+        control.Arrange(new Rect(control.DesiredSize));
+        SetToCenter(control);
         control.OnClose += OnDialogClose;
         control.OnLayerChange += OnDialogLayerChange;
     }
@@ -200,4 +207,16 @@ public class OverlayDialogHost : Canvas
             index++;
         }
     }
+
+    private void SetToCenter(DialogControl? control)
+    {
+        // return;
+        if (control is null) return;
+        double left = (this.Bounds.Width - control.Bounds.Width) / 2;
+        double top = (this.Bounds.Height - control.Bounds.Height) / 2;
+        left = MathUtilities.Clamp(left, 0, Bounds.Width);
+        top = MathUtilities.Clamp(top, 0, Bounds.Height);
+        Canvas.SetLeft(control, left);
+        Canvas.SetTop(control, top);
+    }
 }

src/Ursa/Controls/Dialog/OverlayDialogManager.cs

@@ -7,7 +7,7 @@ internal static class OverlayDialogManager
     private static OverlayDialogHost? _defaultHost;
     private static readonly ConcurrentDictionary<string, OverlayDialogHost> Hosts = new();
     
-    public static void RegisterOverlayDialogHost(OverlayDialogHost host, string? id)
+    public static void RegisterHost(OverlayDialogHost host, string? id)
     {
         if (id == null)
         {
@@ -21,7 +21,7 @@ internal static class OverlayDialogManager
         Hosts.TryAdd(id, host);
     }
     
-    public static void UnregisterOverlayDialogHost(string? id)
+    public static void UnregisterHost(string? id)
     {
         if (id is null)
         {
@@ -31,7 +31,7 @@ internal static class OverlayDialogManager
         Hosts.TryRemove(id, out _);
     }
     
-    public static OverlayDialogHost? GetOverlayDialogHost(string? id)
+    public static OverlayDialogHost? GetHost(string? id)
     {
         if (id is null)
         {