Fix MultipleChoiceFilter: programmatic change of filter does not update ListBox either

Author: tom-englert

src/DataGridExtensions/MultipleChoiceFilter.cs

@@ -23,6 +23,7 @@ public class MultipleChoiceFilter : Control
     {
         private DataGrid? _dataGrid;
         private ListBox? _listBox;
+        private bool _isFilterChanging;
 
         static MultipleChoiceFilter()
         {
@@ -236,31 +237,42 @@ private void ListBox_Loaded(object sender, RoutedEventArgs e)
 
         private void Filter_Changed()
         {
-            var listBox = _listBox;
-            if (listBox == null)
-                return;
+            _isFilterChanging = true;
 
-            var filter = Filter;
+            try
+            {
+                var listBox = _listBox;
+                if (listBox == null)
+                    return;
 
-            Text = filter?.Text;
+                var filter = Filter;
 
-            if (filter?.Items == null)
-            {
-                listBox.SelectAll();
-                return;
-            }
+                Text = filter?.Text;
 
-            if (listBox.SelectedItems.Count != 0)
-                return;
+                if (filter?.Items == null)
+                {
+                    listBox.SelectAll();
+                    return;
+                }
+
+                listBox.SelectedItems.Clear();
 
-            foreach (var item in filter.Items)
+                foreach (var item in filter.Items)
+                {
+                    listBox.SelectedItems.Add(item);
+                }
+            }
+            finally
             {
-                listBox.SelectedItems.Add(item);
+                _isFilterChanging = false;
             }
         }
 
         private void ListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
         {
+            if (_isFilterChanging)
+                return;
+
             var listBox = (ListBox)sender;
 
             if (!listBox.IsLoaded)

src/DataGridExtensionsSample/Views/Customized2View.xaml

@@ -66,13 +66,15 @@
     <DockPanel DockPanel.Dock="Top" Margin="10">
       <DockPanel DockPanel.Dock="Right">
         <StackPanel Orientation="Horizontal" DockPanel.Dock="Top">
-          <Button x:Name="ClearIpsumButton" VerticalAlignment="Top" Padding="5,2" Command="{Binding ClearIpsumCommand}">Clear Ipsum</Button>
+          <Button x:Name="ClearIpsumButton" VerticalAlignment="Top" Padding="5,2" Command="{Binding ClearIpsumCommand}">Remove ipsum from data</Button>
           <Decorator Width="10" />
-          <Button x:Name="OpenAndPopulateAFilterButton" VerticalAlignment="Top" Padding="5,2" Command="{Binding OpenAndPopulateAFilterCommand}">Open &amp; Populate a Filter</Button>
+          <Button VerticalAlignment="Top" Padding="5,2" Command="{Binding AddLoremCommand}">Add lorem to selection</Button>
           <Decorator Width="10" />
-          <Button x:Name="ClearFilter" VerticalAlignment="Top" Padding="5,2" Command="{Binding ClearFilterCommand}" CommandParameter="{Binding ElementName=DemoDataGrid}">Clear Filter</Button>
+          <Button VerticalAlignment="Top" Padding="5,2" Command="{Binding OpenAndPopulateAFilterCommand}">Open &amp; Populate a Filter</Button>
           <Decorator Width="10" />
-          <Button x:Name="ProgrammaticAccessToFilterControlButton" VerticalAlignment="Top" Padding="5,2" Command="{Binding ProgrammaticAccessToFilterControlCommand}">Change Popup Caption</Button>
+          <Button VerticalAlignment="Top" Padding="5,2" Command="{Binding ClearFilterCommand}" CommandParameter="{Binding ElementName=DemoDataGrid}">Clear Filter</Button>
+          <Decorator Width="10" />
+          <Button VerticalAlignment="Top" Padding="5,2" Command="{Binding ProgrammaticAccessToFilterControlCommand}">Change Popup Caption</Button>
         </StackPanel>
         <StackPanel Orientation="Horizontal" DockPanel.Dock="Bottom" HorizontalAlignment="Right">
           <TextBlock Text="Selected: "></TextBlock>

src/DataGridExtensionsSample/Views/Customized2ViewModel.cs

@@ -33,7 +33,7 @@ public Customized2ViewModel(DataProvider dataProvider)
 
         public object? Column5Filter { get; set; }
 
-        public object ColumnTextWithPrefilterFilter { get; set; } = new MultipleChoiceContentFilter(new List<string> { "amet" });
+        public MultipleChoiceContentFilter ColumnTextWithPrefilterFilter { get; set; } = new(new List<string> { "amet" });
 
         public bool Column5PopupVisible { get; set; }
 
@@ -58,6 +58,17 @@ private void ClearIpsum()
             DataProvider.Items.RemoveWhere(item => item.Column5 == "ipsum");
         }
 
+        public ICommand AddLoremCommand => new DelegateCommand(AddLorem);
+
+        private void AddLorem()
+        {
+            var items = ColumnTextWithPrefilterFilter.Items ?? new HashSet<string>();
+
+            items.Add("lorem");
+
+            ColumnTextWithPrefilterFilter = new MultipleChoiceContentFilter(items);
+        }
+
         public ICommand OpenAndPopulateAFilterCommand => new DelegateCommand(OpenAndPopulateAFilter);
 
         private void OpenAndPopulateAFilter()