feat: add ExpandButton

src/Ursa.Themes.Semi/Controls/Pagination.axaml

@@ -19,4 +19,20 @@
             </ControlTemplate>
         </Setter>
     </ControlTheme>
+
+    <ControlTheme x:Key="{x:Type u:PaginationExpandButton}" TargetType="u:PaginationExpandButton">
+        <Setter Property="Template">
+            <ControlTemplate TargetType="u:PaginationExpandButton">
+                <Grid>
+                    <Button Name="button" Content="..." />
+                    <Popup
+                        IsLightDismissEnabled="True"
+                        IsOpen="{Binding #button.IsPointerOver}"
+                        PlacementTarget="button">
+                        <ListBox Background="White" ItemsSource="{TemplateBinding Pages}" />
+                    </Popup>
+                </Grid>
+            </ControlTemplate>
+        </Setter>
+    </ControlTheme>
 </ResourceDictionary>

src/Ursa/Controls/Pagination/Pagination.cs

@@ -23,6 +23,12 @@ public class Pagination: TemplatedControl
     private StackPanel? _buttonPanel;
     private ComboBox? _sizeChangerComboBox;
 
+    /// <summary>
+    /// To reduce allocation, there are maximum of 7 buttons and 2 selection controls. it will be reused.
+    /// </summary>
+    private PaginationExpandButton? _leftSelection;
+    private PaginationExpandButton? _rightSelection;
+
     protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
     {
         base.OnApplyTemplate(e);
@@ -34,6 +40,8 @@ public class Pagination: TemplatedControl
         _sizeChangerComboBox = e.NameScope.Find<ComboBox>(PART_SizeChangerComboBox);
         if (_previousButton != null) _previousButton.Click += OnButtonClick;
         if (_nextButton != null) _nextButton.Click += OnButtonClick;
+        _leftSelection = new PaginationExpandButton();
+        _rightSelection = new PaginationExpandButton();
         UpdateButtons();
 
     }
@@ -60,7 +68,7 @@ public class Pagination: TemplatedControl
     }
 
     public static readonly StyledProperty<int> PageSizeProperty = AvaloniaProperty.Register<Pagination, int>(
-        nameof(PageSize), defaultValue: 100);
+        nameof(PageSize), defaultValue: 50);
     
     /// <summary>
     /// Page size.
@@ -146,8 +154,16 @@ public class Pagination: TemplatedControl
         }
         _buttonPanel?.Children.Clear();
         for (int i = 0; i < pageCount; i++)
+        {
+            if (i == 1 && _leftSelection is not null)
+            {
+                _leftSelection.Pages = new AvaloniaList<int>() { PageSize + 1, PageSize + 2, PageSize + 3 };
+                _buttonPanel?.Children.Add(_leftSelection);
+            }
+            else
             {
                 _buttonPanel?.Children.Add(new Button { Content = i + 1 });
             }
         }
     }
+}

src/Ursa/Controls/Pagination/PaginationExpandButton.cs

@@ -0,0 +1,19 @@
+using Avalonia;
+using Avalonia.Collections;
+using Avalonia.Controls.Primitives;
+
+namespace Ursa.Controls;
+
+public class PaginationExpandButton: TemplatedControl
+{
+    public static readonly StyledProperty<AvaloniaList<int>> PagesProperty = AvaloniaProperty.Register<PaginationExpandButton, AvaloniaList<int>>(
+        nameof(Pages));
+
+    public AvaloniaList<int> Pages
+    {
+        get => GetValue(PagesProperty);
+        set => SetValue(PagesProperty, value);
+    }
+    
+    
+}