feat: initialize dialog.

src/Ursa/Controls/Dialog/DialogBox.cs

@@ -0,0 +1,20 @@
+using Avalonia.Controls;
+
+namespace Ursa.Controls;
+
+public static class DialogBox
+{
+    public static async Task ShowAsync()
+    {
+        return;
+    }
+
+    public static async Task ShowAsync<TView, TViewModel>(TViewModel vm) 
+        where TView: Control, new()
+        where TViewModel: new()
+    {
+        TView t = new TView();
+        t.DataContext = vm;
+        return;
+    }
+}

src/Ursa/Controls/Dialog/DialogControl.cs

@@ -0,0 +1,8 @@
+using Avalonia.Controls;
+
+namespace Ursa.Controls;
+
+public class DialogControl: ContentControl
+{
+    
+}

src/Ursa/Controls/Dialog/DialogHost.cs

@@ -0,0 +1,39 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Controls.Primitives;
+using Avalonia.Input;
+using Avalonia.Utilities;
+
+namespace Ursa.Controls;
+
+public class DialogHost: Canvas
+{
+    private Point _lastPoint;
+    
+    protected override void OnPointerMoved(PointerEventArgs e)
+    {
+        base.OnPointerMoved(e);
+        if (e.Source is DialogControl item)
+        {
+            if (e.GetCurrentPoint(this).Properties.IsLeftButtonPressed)
+            {
+                var p = e.GetPosition(this);
+                var left=  p.X - _lastPoint.X;
+                var top = p.Y - _lastPoint.Y;
+                left = MathUtilities.Clamp(left, 0, Bounds.Width - item.Bounds.Width);
+                top = MathUtilities.Clamp(top, 0, Bounds.Height - item.Bounds.Height);
+                Canvas.SetLeft(item, left);
+                Canvas.SetTop(item, top);
+            }
+        }
+    }
+
+    protected override void OnPointerPressed(PointerPressedEventArgs e)
+    {
+        base.OnPointerPressed(e);
+        if (e.Source is DialogControl item)
+        {
+            _lastPoint = e.GetPosition(item);
+        }
+    }
+}

src/Ursa/Controls/Dialog/IDialogContext.cs

@@ -0,0 +1,6 @@
+namespace Ursa.Controls;
+
+public interface IDialogContext
+{
+    
+}