fix virtualisation if a SelectedItem is bound wo a combobox #119

Author: ButchersBoy

MainDemo.Wpf/Domain/TextFieldsViewModel.cs

@@ -4,6 +4,7 @@
 using System.Linq;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
+using System.Security.Cryptography.X509Certificates;
 using System.Text;
 using System.Threading.Tasks;
 
@@ -14,10 +15,13 @@ public class TextFieldsViewModel : INotifyPropertyChanged
         private readonly IList<int> _longListToTestComboVirtualization;
 
         private string _name;
+        private int _selectedValueOne;
 
         public TextFieldsViewModel()
         {
-            _longListToTestComboVirtualization = new List<int>(Enumerable.Range(0, 1000));            
+            _longListToTestComboVirtualization = new List<int>(Enumerable.Range(0, 1000));
+
+            SelectedValueOne = _longListToTestComboVirtualization.Skip(2).First();
         }
 
         public string Name
@@ -30,6 +34,16 @@ public string Name
             }
         }
 
+        public int SelectedValueOne
+        {
+            get { return _selectedValueOne; }
+            set
+            {
+                _selectedValueOne = value;
+                OnPropertyChanged();
+            }
+        }
+
         public IList<int> LongListToTestComboVirtualization => _longListToTestComboVirtualization;
 
         public event PropertyChangedEventHandler PropertyChanged;

MainDemo.Wpf/TextFields.xaml

@@ -5,8 +5,10 @@
              xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
              xmlns:wpf="clr-namespace:MaterialDesignThemes.Wpf;assembly=MaterialDesignThemes.Wpf"
              xmlns:wpfExample="clr-namespace:MaterialDesignColors.WpfExample"
+             xmlns:domain="clr-namespace:MaterialDesignColors.WpfExample.Domain"
              mc:Ignorable="d"               
-             d:DesignHeight="300" d:DesignWidth="600" Loaded="UserControl_Loaded">
+             d:DesignHeight="300" d:DesignWidth="600" Loaded="UserControl_Loaded"
+             d:DataContext="{d:DesignInstance domain:TextFieldsViewModel, d:IsDesignTimeCreatable=False}">
     <UserControl.Resources>
         <ResourceDictionary>
             <ResourceDictionary.MergedDictionaries>
@@ -132,8 +134,9 @@
 
         <StackPanel Grid.Row="4" Grid.Column="4" Orientation="Horizontal">
             <ComboBox wpf:TextFieldAssist.Hint="Virtualisation" 
-                  HorizontalAlignment="Left" Margin="16 0 0 0"
-                  ItemsSource="{Binding LongListToTestComboVirtualization}">
+                      HorizontalAlignment="Left" Margin="16 0 0 0"
+                      ItemsSource="{Binding LongListToTestComboVirtualization}"
+                      SelectedValue="{Binding SelectedValueOne}">
                 <ComboBox.ItemsPanel>
                     <ItemsPanelTemplate>
                         <VirtualizingStackPanel />

MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.ComboBox.xaml

@@ -124,7 +124,7 @@
                     <Condition Property="Tag" Value="1.0"/>
                     <Condition Property="IsSelected" Value="True"/>
                 </MultiTrigger.Conditions>
-                <Setter Property="Visibility" Value="Collapsed"/>
+                <Setter Property="Height" Value="0"/>
             </MultiTrigger>
         </ControlTemplate.Triggers>
     </ControlTemplate>