fix: the colon should invisible when ItemsAlignmen=Plain. (#884)

* fix: the colon should invisible when ItemsAlignmen=Plain.

* test: add HeadlessTest for colon visibility in DescriptionsItem Plain mode (#885)

* Initial plan

* test: add HeadlessTest for colon visibility in Plain mode

Co-authored-by: zdpcdt <54255897+zdpcdt@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: zdpcdt <54255897+zdpcdt@users.noreply.github.com>

---------

Co-authored-by: Copilot <198982749+Copilot@users.noreply.github.com>

Author: zdpcdt

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

@@ -103,6 +103,11 @@
                     <Setter Property="HorizontalAlignment" Value="Right" />
                 </Style>
             </Style>
+            <Style Selector="^[ItemAlignment=Plain]">
+                <Style Selector="^ /template/ TextBlock#PART_Colon">
+                    <Setter Property="IsVisible" Value="{TemplateBinding Label, Converter={x:Static StringConverters.IsNotNullOrEmpty}}" />
+                </Style>
+            </Style>
         </Style>
         <Style Selector="^:vertical">
             <Setter Property="iri:ClassHelper.ClassSource" Value="{Binding $parent[u:Descriptions]}" />

tests/HeadlessTest.Ursa/Controls/DescriptionTests/Test.cs

@@ -1,7 +1,10 @@
 using Avalonia.Controls;
+using Avalonia.Controls.Primitives;
 using Avalonia.Data;
 using Avalonia.Headless.XUnit;
 using Avalonia.LogicalTree;
+using Avalonia.Threading;
+using HeadlessTest.Ursa.TestHelpers;
 using Ursa.Common;
 using Ursa.Controls;
 
@@ -180,4 +183,80 @@ public void Descriptions_LabelWidth_Propagates_To_DescriptionItems()
             Assert.Equal(150, item.LabelWidth);
         }
     }
+
+    [AvaloniaFact]
+    public void DescriptionItem_Colon_Visibility_When_ItemAlignment_Is_Plain()
+    {
+        // Test case 1: ItemAlignment=Plain with non-empty Label - colon should be visible
+        var itemWithLabel = new DescriptionsItem
+        {
+            Label = "Name",
+            Content = "John Doe",
+            ItemAlignment = ItemAlignment.Plain,
+            LabelPosition = Position.Left
+        };
+        var window1 = new Window { Content = itemWithLabel };
+        window1.Show();
+        Dispatcher.UIThread.RunJobs();
+
+        var colon1 = itemWithLabel.GetTemplateChildOfType<TextBlock>("PART_Colon");
+        Assert.NotNull(colon1);
+        Assert.True(colon1.IsVisible, "Colon should be visible when ItemAlignment=Plain and Label is not empty");
+
+        window1.Close();
+
+        // Test case 2: ItemAlignment=Plain with null Label - colon should be hidden
+        var itemWithoutLabel = new DescriptionsItem
+        {
+            Label = null,
+            Content = "John Doe",
+            ItemAlignment = ItemAlignment.Plain,
+            LabelPosition = Position.Left
+        };
+        var window2 = new Window { Content = itemWithoutLabel };
+        window2.Show();
+        Dispatcher.UIThread.RunJobs();
+
+        var colon2 = itemWithoutLabel.GetTemplateChildOfType<TextBlock>("PART_Colon");
+        Assert.NotNull(colon2);
+        Assert.False(colon2.IsVisible, "Colon should be hidden when ItemAlignment=Plain and Label is null");
+
+        window2.Close();
+
+        // Test case 3: ItemAlignment=Plain with empty string Label - colon should be hidden
+        var itemWithEmptyLabel = new DescriptionsItem
+        {
+            Label = string.Empty,
+            Content = "John Doe",
+            ItemAlignment = ItemAlignment.Plain,
+            LabelPosition = Position.Left
+        };
+        var window3 = new Window { Content = itemWithEmptyLabel };
+        window3.Show();
+        Dispatcher.UIThread.RunJobs();
+
+        var colon3 = itemWithEmptyLabel.GetTemplateChildOfType<TextBlock>("PART_Colon");
+        Assert.NotNull(colon3);
+        Assert.False(colon3.IsVisible, "Colon should be hidden when ItemAlignment=Plain and Label is empty string");
+
+        window3.Close();
+
+        // Test case 4: ItemAlignment=Center with Label - colon should be hidden (per existing style)
+        var itemWithCenterAlignment = new DescriptionsItem
+        {
+            Label = "Age",
+            Content = "30",
+            ItemAlignment = ItemAlignment.Center,
+            LabelPosition = Position.Left
+        };
+        var window4 = new Window { Content = itemWithCenterAlignment };
+        window4.Show();
+        Dispatcher.UIThread.RunJobs();
+
+        var colon4 = itemWithCenterAlignment.GetTemplateChildOfType<TextBlock>("PART_Colon");
+        Assert.NotNull(colon4);
+        Assert.False(colon4.IsVisible, "Colon should be hidden when ItemAlignment=Center (regardless of Label)");
+
+        window4.Close();
+    }
 }