feat: move identification to measure process.

demo/Ursa.Demo/Pages/ToolBarDemo.axaml

@@ -10,7 +10,7 @@
              mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
              x:Class="Ursa.Demo.Pages.ToolBarDemo">
     <StackPanel>
-        <u:ToolBar HorizontalAlignment="Left">
+        <u:ToolBar HorizontalAlignment="Left" Header="Hello World">
             <Button Content="Button 1" />
             <Button Content="Button 2" />
             <Button Content="Button 3" u:ToolBar.OverflowMode="Always" />
@@ -20,6 +20,5 @@
                 <template:ToolBarItemTemplateSelector/>
             </u:ToolBar.ItemTemplate>
         </u:ToolBar>
-        <CheckBox Content="Check"></CheckBox>
     </StackPanel>
 </UserControl>

src/Ursa/Controls/ToolBar/ToolBar.cs

@@ -38,10 +38,16 @@ public class ToolBar: HeaderedItemsControl
     }
 
     public static readonly AttachedProperty<OverflowMode> OverflowModeProperty =
-        AvaloniaProperty.RegisterAttached<ToolBar, Control?, OverflowMode>("OverflowMode");
+        AvaloniaProperty.RegisterAttached<ToolBar, Control, OverflowMode>("OverflowMode");
 
-    public static void SetOverflowMode(Control? obj, OverflowMode value) => obj.SetValue(OverflowModeProperty, value);
+    public static void SetOverflowMode(Control obj, OverflowMode value) => obj.SetValue(OverflowModeProperty, value);
-    public static OverflowMode GetOverflowMode(Control? obj) => obj.GetValue(OverflowModeProperty);
+    public static OverflowMode GetOverflowMode(Control obj) => obj.GetValue(OverflowModeProperty);
+
+    internal static readonly AttachedProperty<bool> IsOverflowItemProperty =
+        AvaloniaProperty.RegisterAttached<ToolBar, Control, bool>("IsOverflowItem");
+
+    internal static void SetIsOverflowItem(Control obj, bool value) => obj.SetValue(IsOverflowItemProperty, value);
+    internal static bool GetIsOverflowItem(Control obj) => obj.GetValue(IsOverflowItemProperty);
 
     static ToolBar()
     {

src/Ursa/Controls/ToolBar/ToolBarPanel.cs

@@ -2,7 +2,6 @@
 using Avalonia.Controls;
 using Avalonia.Layout;
 using Avalonia.LogicalTree;
-using Avalonia.VisualTree;
 
 namespace Ursa.Controls;
 
@@ -45,16 +44,18 @@ public class ToolBarPanel: StackPanel
         Size measureSize = availableSize;
         bool horizontal = Orientation == Orientation.Horizontal;
         bool hasVisibleChildren = false;
-        measureSize = horizontal
+        measureSize = new Size(double.PositiveInfinity, double.PositiveInfinity);
-            ? measureSize.WithWidth(double.PositiveInfinity)
-            : measureSize.WithHeight(double.PositiveInfinity);
         int index = 0;
         if (logicalChildren is null) return size;
         for (int count = logicalChildren.Count; index < count; ++index)
         {
             Control control = logicalChildren[index];
             var mode = ToolBar.GetOverflowMode(control);
-            if(mode == OverflowMode.Always) continue;
+            if (mode == OverflowMode.Always)
+            {
+                ToolBar.SetIsOverflowItem(control, true);
+                continue;
+            }
             bool isVisible = control.IsVisible;
             if (isVisible)
             {
@@ -83,6 +84,21 @@ public class ToolBarPanel: StackPanel
 
     protected override Size ArrangeOverride(Size finalSize)
     {
+        var logicalChildren = _parent?.GetLogicalChildren().OfType<Control>().ToList();
+        Children.Clear();
+        OverflowPanel?.Children.Clear();
+        foreach (var child in logicalChildren)
+        {
+            if (ToolBar.GetIsOverflowItem(child))
+            {
+                OverflowPanel?.Children.Add(child);
+            }
+            else
+            {
+                this.Children.Add(child);
+            }
+        }
+        return base.ArrangeOverride(finalSize);
         if (_parent is null)
         {
             return finalSize;