test: ComboBox_ReopenDropdown

Author: ramezgerges

src/SamplesApp/UITests.Shared/UITests.Shared.projitems

@@ -3066,6 +3066,10 @@
       <SubType>Designer</SubType>
       <Generator>MSBuild:Compile</Generator>
     </Page>
+    <Page Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Controls\Button\ComboBox_ReopenDropdown.xaml">
+      <SubType>Designer</SubType>
+      <Generator>MSBuild:Compile</Generator>
+    </Page>
     <Page Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Controls\Button\Custom_Button_With_ContentTemplate.xaml">
       <SubType>Designer</SubType>
       <Generator>MSBuild:Compile</Generator>
@@ -9158,6 +9162,9 @@
     <Compile Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Controls\Button\ComboBox_Simple.xaml.cs">
       <DependentUpon>ComboBox_Simple.xaml</DependentUpon>
     </Compile>
+    <Compile Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Controls\Button\ComboBox_ReopenDropdown.xaml.cs">
+      <DependentUpon>ComboBox_ReopenDropdown.xaml</DependentUpon>
+    </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Controls\Button\Custom_Button_With_ContentTemplate.xaml.cs">
       <DependentUpon>Custom_Button_With_ContentTemplate.xaml</DependentUpon>
     </Compile>

src/SamplesApp/UITests.Shared/Windows_UI_Xaml_Controls/Button/ComboBox_ReopenDropdown.xaml

@@ -0,0 +1,17 @@
+<UserControl
+	x:Class="Uno.UI.Samples.Content.UITests.ButtonTestsControl.ComboBox_ReopenDropdown" 
+	xmlns:controls="using:Uno.UI.Samples.Controls"
+	xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+	xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+	xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+	xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+	xmlns:not_win="http://uno.ui/not_win"
+	mc:Ignorable="d not_win"
+	d:DesignHeight="300"
+	d:DesignWidth="400">
+
+	<StackPanel>
+		<TextBlock Text="Open the ComboBox, scroll down and select item 10000. Open the ComboBox again. It should immediately open with the selected item showing without a large delay." />
+		<ComboBox x:Name="cb" />
+	</StackPanel>
+</UserControl>

src/SamplesApp/UITests.Shared/Windows_UI_Xaml_Controls/Button/ComboBox_ReopenDropdown.xaml.cs

@@ -0,0 +1,16 @@
+using System.Linq;
+using Uno.UI.Samples.Controls;
+using Microsoft.UI.Xaml.Controls;
+
+namespace Uno.UI.Samples.Content.UITests.ButtonTestsControl
+{
+	[Sample("Buttons", IsManualTest = true)]
+	public sealed partial class ComboBox_ReopenDropdown : UserControl
+	{
+		public ComboBox_ReopenDropdown()
+		{
+			this.InitializeComponent();
+			cb.ItemsSource = Enumerable.Range(0, 20000).ToArray();
+		}
+	}
+}