Fix flickering & add result highlighting

- Implemented channel-based debouncing (20ms) in MainViewModel to fix result flickering (matches WPF behavior)

- Added ResultForUpdate struct and ProcessResultUpdatesAsync for batching updates

- Added HighlightTextConverter and TextBlockHelper for bolding matched query terms

- Updated ResultListBox to display highlighted title and subtitle

Flow.Launcher.Avalonia/Converters/CommonConverters.cs

@@ -1,26 +1,64 @@
 using System;
 using System.Collections.Generic;
 using System.Globalization;
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Controls.Documents;
 using Avalonia.Data.Converters;
 using Avalonia.Media;
 
 namespace Flow.Launcher.Avalonia.Converters;
 
 /// <summary>
-/// Converts text with highlight ranges to formatted text with bold highlights.
-/// This is a simplified version - full implementation would use Avalonia's TextDecorations.
+/// Converts text with highlight indices to InlineCollection with bold highlights.
+/// Usage: MultiBinding with [0]=text string, [1]=List&lt;int&gt; of character indices to highlight.
 /// </summary>
 public class HighlightTextConverter : IMultiValueConverter
 {
     public object? Convert(IList<object?> values, Type targetType, object? parameter, CultureInfo culture)
     {
-        // For now, just return the plain text
-        // Full implementation would create formatted inline text with highlights
-        if (values.Count >= 1 && values[0] is string text)
+        if (values.Count < 1 || values[0] is not string text || string.IsNullOrEmpty(text))
+            return new InlineCollection { new Run(string.Empty) };
+
+        // If no highlight data, return plain text as single Run
+        if (values.Count < 2 || values[1] is not IList<int> { Count: > 0 } highlightData)
+            return new InlineCollection { new Run(text) };
+
+        var inlines = new InlineCollection();
+        var highlightSet = new HashSet<int>(highlightData);
+
+        // Build runs by grouping consecutive characters with same highlight state
+        var currentRun = new System.Text.StringBuilder();
+        var currentIsHighlight = highlightSet.Contains(0);
+
+        for (var i = 0; i < text.Length; i++)
         {
-            return text;
+            var shouldHighlight = highlightSet.Contains(i);
+
+            if (shouldHighlight != currentIsHighlight && currentRun.Length > 0)
+            {
+                // Flush current run
+                inlines.Add(CreateRun(currentRun.ToString(), currentIsHighlight));
+                currentRun.Clear();
+                currentIsHighlight = shouldHighlight;
+            }
+
+            currentRun.Append(text[i]);
         }
-        return string.Empty;
+
+        // Flush final run
+        if (currentRun.Length > 0)
+            inlines.Add(CreateRun(currentRun.ToString(), currentIsHighlight));
+
+        return inlines;
+    }
+
+    private static Run CreateRun(string text, bool isHighlight)
+    {
+        var run = new Run(text);
+        if (isHighlight)
+            run.FontWeight = FontWeight.Bold;
+        return run;
     }
 }
 

Flow.Launcher.Avalonia/Helper/TextBlockHelper.cs

@@ -0,0 +1,57 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Controls.Documents;
+
+namespace Flow.Launcher.Avalonia.Helper;
+
+/// <summary>
+/// Attached properties for TextBlock to enable binding Inlines from converters.
+/// </summary>
+public static class TextBlockHelper
+{
+    /// <summary>
+    /// Attached property for setting formatted text with highlights on a TextBlock.
+    /// Bind to this with a MultiBinding + HighlightTextConverter to get highlighted search results.
+    /// </summary>
+    public static readonly AttachedProperty<InlineCollection?> FormattedTextProperty =
+        AvaloniaProperty.RegisterAttached<TextBlock, InlineCollection?>(
+            "FormattedText",
+            typeof(TextBlockHelper));
+
+    static TextBlockHelper()
+    {
+        FormattedTextProperty.Changed.AddClassHandler<TextBlock>(OnFormattedTextChanged);
+    }
+
+    public static InlineCollection? GetFormattedText(TextBlock textBlock)
+        => textBlock.GetValue(FormattedTextProperty);
+
+    public static void SetFormattedText(TextBlock textBlock, InlineCollection? value)
+        => textBlock.SetValue(FormattedTextProperty, value);
+
+    private static void OnFormattedTextChanged(TextBlock textBlock, AvaloniaPropertyChangedEventArgs e)
+    {
+        textBlock.Inlines?.Clear();
+
+        if (e.NewValue is InlineCollection inlines)
+        {
+            // We need to copy the inlines because they can only belong to one parent
+            foreach (var inline in inlines)
+            {
+                if (inline is Run run)
+                {
+                    var newRun = new Run(run.Text)
+                    {
+                        FontWeight = run.FontWeight
+                    };
+                    textBlock.Inlines?.Add(newRun);
+                }
+                else
+                {
+                    // For other inline types, add directly (may need enhancement)
+                    textBlock.Inlines?.Add(inline);
+                }
+            }
+        }
+    }
+}

Flow.Launcher.Avalonia/MainWindow.axaml

@@ -86,7 +86,8 @@
                        IsVisible="{Binding ShowResultsArea}" />
 
             <!-- Results Area -->
-            <Border Name="ResultAreaBorder" Classes="resultAreaBorder">
+            <Border Name="ResultAreaBorder" Classes="resultAreaBorder"
+                    IsVisible="{Binding ShowResultsArea}">
                 <Grid Name="ResultPreviewArea">
                     <Grid.ColumnDefinitions>
                         <ColumnDefinition Width="*" MinWidth="80" />

Flow.Launcher.Avalonia/ViewModel/MainViewModel.cs

@@ -3,6 +3,7 @@ using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
+using System.Threading.Channels;
 using System.Threading.Tasks;
 using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
@@ -34,6 +35,11 @@ public partial class MainViewModel : ObservableObject
     private CancellationTokenSource? _queryTokenSource;
     private bool _pluginsReady;
 
+    // Channel-based debouncing for result updates (matches WPF approach)
+    private readonly Channel<ResultsForUpdate> _resultsUpdateChannel;
+    private readonly ChannelWriter<ResultsForUpdate> _resultsUpdateChannelWriter;
+    private readonly Task _resultsViewUpdateTask;
+
     public event Action? HideRequested;
     public event Action? ShowRequested;
 
@@ -76,8 +82,9 @@ public partial class MainViewModel : ObservableObject
 
     /// <summary>
     /// Whether to show the results/context menu area (separator + list).
+    /// Based on whether we have a non-empty query - NOT on collection count to prevent flickering.
     /// </summary>
-    public bool ShowResultsArea => HasResults || IsContextMenuViewActive;
+    public bool ShowResultsArea => !string.IsNullOrWhiteSpace(QueryText) || ContextMenu.Results.Count > 0;
 
     public Settings Settings => _settings;
 
@@ -86,6 +93,11 @@ public partial class MainViewModel : ObservableObject
         _settings = settings;
         _results = new ResultsViewModel(settings);
         _contextMenu = new ResultsViewModel(settings);
+
+        // Initialize channel-based debouncing for result updates
+        _resultsUpdateChannel = Channel.CreateUnbounded<ResultsForUpdate>();
+        _resultsUpdateChannelWriter = _resultsUpdateChannel.Writer;
+        _resultsViewUpdateTask = Task.Run(ProcessResultUpdatesAsync);
         
         _results.PropertyChanged += (s, e) =>
         {
@@ -102,6 +114,51 @@ public partial class MainViewModel : ObservableObject
                 PreviewSelectedItem = _contextMenu.SelectedItem;
             }
         };
+        
+        // Subscribe to context menu collection changes for ShowResultsArea (context menu still uses count)
+        ((System.Collections.Specialized.INotifyCollectionChanged)_contextMenu.Results).CollectionChanged += (s, e) => OnPropertyChanged(nameof(ShowResultsArea));
+    }
+
+    /// <summary>
+    /// Background task that processes result updates with debouncing.
+    /// Waits 20ms to batch multiple plugin completions into a single UI update.
+    /// </summary>
+    private async Task ProcessResultUpdatesAsync()
+    {
+        var channelReader = _resultsUpdateChannel.Reader;
+
+        while (await channelReader.WaitToReadAsync())
+        {
+            // Wait 20ms to allow multiple plugin results to arrive
+            await Task.Delay(20);
+
+            // Get the latest snapshot from the channel (discard intermediate ones)
+            ResultsForUpdate? latestUpdate = null;
+
+            while (channelReader.TryRead(out var update))
+            {
+                if (!update.Token.IsCancellationRequested)
+                {
+                    latestUpdate = update;
+                }
+            }
+
+            // Apply batched update on UI thread
+            if (latestUpdate.HasValue && !latestUpdate.Value.Token.IsCancellationRequested)
+            {
+                var update = latestUpdate.Value;
+                var sortedResults = update.Results
+                    .OrderByDescending(r => r.Score)
+                    .ToList();
+
+                await global::Avalonia.Threading.Dispatcher.UIThread.InvokeAsync(() =>
+                {
+                    if (update.Token.IsCancellationRequested) return;
+                    Results.ReplaceResults(sortedResults);
+                    HasResults = Results.Results.Count > 0;
+                });
+            }
+        }
     }
 
     partial void OnActiveViewChanged(ActiveView value)
@@ -113,17 +170,17 @@ public partial class MainViewModel : ObservableObject
         PreviewSelectedItem = value == ActiveView.Results ? Results.SelectedItem : ContextMenu.SelectedItem;
     }
 
+    partial void OnIsQueryRunningChanged(bool value)
+    {
+        // ShowResultsArea no longer depends on IsQueryRunning - it uses QueryText instead
+    }
+
     [RelayCommand]
     public void TogglePreview()
     {
         IsPreviewOn = !IsPreviewOn;
     }
 
-    partial void OnHasResultsChanged(bool value)
-    {
-        OnPropertyChanged(nameof(ShowResultsArea));
-    }
-
     public void OnPluginsReady()
     {
         _pluginsReady = true;
@@ -184,7 +241,12 @@ public partial class MainViewModel : ObservableObject
         ContextMenu.Clear();
     }
 
-    partial void OnQueryTextChanged(string value) => _ = QueryAsync();
+    partial void OnQueryTextChanged(string value)
+    {
+        // Notify ShowResultsArea when query text changes (it depends on QueryText)
+        OnPropertyChanged(nameof(ShowResultsArea));
+        _ = QueryAsync();
+    }
 
     private async Task QueryAsync()
     {
@@ -213,12 +275,22 @@ public partial class MainViewModel : ObservableObject
         try
         {
             var query = QueryBuilder.Build(queryText, PluginManager.NonGlobalPlugins);
-            if (query == null) { HasResults = false; return; }
+            if (query == null)
+            {
+                Results.Clear();
+                HasResults = false;
+                return;
+            }
 
             var plugins = PluginManager.ValidPluginsForQuery(query, dialogJump: false)
                 .Where(p => !p.Metadata.Disabled).ToList();
 
-            if (plugins.Count == 0) { HasResults = false; return; }
+            if (plugins.Count == 0)
+            {
+                Results.Clear();
+                HasResults = false;
+                return;
+            }
 
             // Use a thread-safe collection to accumulate results from all plugins
             var allResults = new ConcurrentBag<ResultViewModel>();
@@ -235,10 +307,10 @@ public partial class MainViewModel : ObservableObject
                     allResults.Add(r);
                 }
 
-                // Update UI with current accumulated results (progressive update)
+                // Update UI with current accumulated results (progressive update via channel)
                 if (!token.IsCancellationRequested)
                 {
-                    await UpdateResultsOnUIThread(allResults, token);
+                    _resultsUpdateChannelWriter.TryWrite(new ResultsForUpdate(allResults.ToList(), token));
                 }
             });
 
@@ -247,7 +319,7 @@ public partial class MainViewModel : ObservableObject
             // Final update after all plugins complete
             if (!token.IsCancellationRequested)
             {
-                await UpdateResultsOnUIThread(allResults, token);
+                _resultsUpdateChannelWriter.TryWrite(new ResultsForUpdate(allResults.ToList(), token));
             }
         }
         catch (OperationCanceledException) { }
@@ -255,23 +327,6 @@ public partial class MainViewModel : ObservableObject
         finally { if (!token.IsCancellationRequested) IsQueryRunning = false; }
     }
 
-    private async Task UpdateResultsOnUIThread(ConcurrentBag<ResultViewModel> allResults, CancellationToken token)
-    {
-        if (token.IsCancellationRequested) return;
-
-        var sortedResults = allResults
-            .OrderByDescending(r => r.Score)
-            .Take(_settings.MaxResultsToShow)
-            .ToList();
-
-        await global::Avalonia.Threading.Dispatcher.UIThread.InvokeAsync(() =>
-        {
-            if (token.IsCancellationRequested) return;
-            Results.ReplaceResults(sortedResults);
-            HasResults = Results.Results.Count > 0;
-        });
-    }
-
     private Task<List<ResultViewModel>> QueryPluginAsync(PluginPair plugin, Query query, CancellationToken token)
     {
         // Run entirely on thread pool to avoid blocking UI if plugin has synchronous code
@@ -297,7 +352,8 @@ public partial class MainViewModel : ObservableObject
                         IconPath = r.IcoPath ?? plugin.Metadata.IcoPath ?? "",
                         Score = r.Score,
                         PluginResult = r,
-                        Glyph = r.Glyph
+                        Glyph = r.Glyph,
+                        TitleHighlightData = r.TitleHighlightData
                     });
                 }
             }
@@ -414,3 +470,19 @@ public partial class MainViewModel : ObservableObject
             Results.SelectPrevItem();
     }
 }
+
+/// <summary>
+/// Represents a batch of results from a plugin for UI update.
+/// Used for channel-based debouncing.
+/// </summary>
+internal readonly struct ResultsForUpdate
+{
+    public IReadOnlyList<ResultViewModel> Results { get; }
+    public CancellationToken Token { get; }
+
+    public ResultsForUpdate(IReadOnlyList<ResultViewModel> results, CancellationToken token)
+    {
+        Results = results;
+        Token = token;
+    }
+}

Flow.Launcher.Avalonia/ViewModel/ResultViewModel.cs

@@ -1,3 +1,4 @@
+using System.Collections.Generic;
 using System.Threading.Tasks;
 using Avalonia.Media;
 using CommunityToolkit.Mvvm.ComponentModel;
@@ -30,6 +31,12 @@ public partial class ResultViewModel : ObservableObject
     [ObservableProperty]
     private int _score;
 
+    [ObservableProperty]
+    private IList<int>? _titleHighlightData;
+
+    [ObservableProperty]
+    private IList<int>? _subTitleHighlightData;
+
     /// <summary>
     /// The underlying plugin result. Used for executing actions and accessing additional properties.
     /// </summary>

Flow.Launcher.Avalonia/ViewModel/ResultsViewModel.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
+using System.Linq;
 using CommunityToolkit.Mvvm.ComponentModel;
 using DynamicData;
 using DynamicData.Binding;
@@ -50,18 +51,19 @@ public partial class ResultsViewModel : ObservableObject, IDisposable
     }
 
     /// <summary>
-    /// Replace all results with new ones using EditDiff to minimize UI updates.
-    /// Items with matching Title+SubTitle are kept, reducing flickering.
+    /// Replace all results with new ones using atomic Edit to prevent flickering.
+    /// Edit batches changes and fires only one notification at the end.
     /// </summary>
     public void ReplaceResults(IEnumerable<ResultViewModel> newResults)
     {
-        foreach (var r in newResults)
+        var resultsList = newResults.ToList();
+        foreach (var r in resultsList)
         {
             r.Settings = _settings;
         }
 
-        // EditDiff calculates minimal changes needed
-        _sourceList.EditDiff(newResults, ResultViewModelComparer.Instance);
+        // EditDiff calculates minimal changes needed - items with same Title+SubTitle are kept
+        _sourceList.EditDiff(resultsList, ResultViewModelComparer.Instance);
 
         // Select first item after replacement
         if (_results.Count > 0)

Flow.Launcher.Avalonia/Views/ResultListBox.axaml

@@ -4,9 +4,14 @@
              xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
              xmlns:vm="using:Flow.Launcher.Avalonia.ViewModel"
              xmlns:helper="using:Flow.Launcher.Avalonia.Helper"
+             xmlns:converters="using:Flow.Launcher.Avalonia.Converters"
              mc:Ignorable="d" d:DesignWidth="580" d:DesignHeight="300"
              x:Class="Flow.Launcher.Avalonia.Views.ResultListBox"
              x:DataType="vm:ResultsViewModel">
+    
+    <UserControl.Resources>
+        <converters:HighlightTextConverter x:Key="HighlightTextConverter" />
+    </UserControl.Resources>
      
     <ListBox Name="ResultsList"
              Classes="resultListBox"
@@ -64,14 +69,26 @@
                             
                             <TextBlock Grid.Row="0"
                                        Classes="resultTitle"
-                                       Text="{Binding Title}"
-                                       ToolTip.Tip="{Binding Title}" />
+                                       ToolTip.Tip="{Binding Title}">
+                                <helper:TextBlockHelper.FormattedText>
+                                    <MultiBinding Converter="{StaticResource HighlightTextConverter}">
+                                        <Binding Path="Title" />
+                                        <Binding Path="TitleHighlightData" />
+                                    </MultiBinding>
+                                </helper:TextBlockHelper.FormattedText>
+                            </TextBlock>
                             
                             <TextBlock Grid.Row="1"
                                        Classes="resultSubTitle"
-                                       Text="{Binding SubTitle}"
                                        IsVisible="{Binding ShowSubTitle}"
-                                       ToolTip.Tip="{Binding SubTitle}" />
+                                       ToolTip.Tip="{Binding SubTitle}">
+                                <helper:TextBlockHelper.FormattedText>
+                                    <MultiBinding Converter="{StaticResource HighlightTextConverter}">
+                                        <Binding Path="SubTitle" />
+                                        <Binding Path="SubTitleHighlightData" />
+                                    </MultiBinding>
+                                </helper:TextBlockHelper.FormattedText>
+                            </TextBlock>
                         </Grid>
                     </Grid>