Add small delay to the search query before displaying results (#18290)

* Add small delay to the search query before displaying results

* Reduce user input throttle to 150ms and fix issue with autocomplete text updating

* Add System.Reactive.dll to Launcher installer

src/modules/launcher/PowerLauncher/MainWindow.xaml.cs

@@ -5,6 +5,7 @@
 using System;
 using System.ComponentModel;
 using System.Linq;
+using System.Reactive.Linq;
 using System.Runtime.InteropServices;
 using System.Timers;
 using System.Windows;
@@ -159,7 +160,14 @@ namespace PowerLauncher
 
             SearchBox.QueryTextBox.DataContext = _viewModel;
             SearchBox.QueryTextBox.PreviewKeyDown += Launcher_KeyDown;
-            SearchBox.QueryTextBox.TextChanged += QueryTextBox_TextChanged;
+
+            Observable.FromEventPattern<TextChangedEventHandler, TextChangedEventArgs>(
+                add => SearchBox.QueryTextBox.TextChanged += add,
+                remove => SearchBox.QueryTextBox.TextChanged -= remove)
+                    .Do(@event => ClearAutoCompleteText((TextBox)@event.Sender))
+                    .Throttle(TimeSpan.FromMilliseconds(150))
+                    .Do(@event => Dispatcher.InvokeAsync(() => PerformSearchQuery((TextBox)@event.Sender)))
+                    .Subscribe();
 
             // Set initial language flow direction
             SearchBox_UpdateFlowDirection();
@@ -413,7 +421,7 @@ namespace PowerLauncher
 
             // To populate the AutoCompleteTextBox as soon as the selection is changed or set.
             // Setting it here instead of when the text is changed as there is a delay in executing the query and populating the result
-            if (_viewModel.Results != null)
+            if (_viewModel.Results != null && !string.IsNullOrEmpty(SearchBox.QueryTextBox.Text))
             {
                 SearchBox.AutoCompleteTextBlock.Text = MainViewModel.GetAutoCompleteText(
                     _viewModel.Results.SelectedIndex,
@@ -422,9 +430,8 @@ namespace PowerLauncher
             }
         }
 
-        private void QueryTextBox_TextChanged(object sender, TextChangedEventArgs e)
+        private void ClearAutoCompleteText(TextBox textBox)
         {
-            var textBox = (TextBox)sender;
             var text = textBox.Text;
             var autoCompleteText = SearchBox.AutoCompleteTextBlock.Text;
 
@@ -432,6 +439,11 @@ namespace PowerLauncher
             {
                 SearchBox.AutoCompleteTextBlock.Text = string.Empty;
             }
+        }
+
+        private void PerformSearchQuery(TextBox textBox)
+        {
+            var text = textBox.Text;
 
             if (_isTextSetProgrammatically)
             {

src/modules/launcher/PowerLauncher/PowerLauncher.csproj

@@ -88,6 +88,7 @@
     <PackageReference Include="Microsoft.Toolkit.Uwp.Notifications" Version="7.1.2" />
     <PackageReference Include="Microsoft.Xaml.Behaviors.Wpf" Version="1.1.39" />
     <PackageReference Include="ModernWpfUI" Version="0.9.4" />
+    <PackageReference Include="System.Reactive" Version="5.0.0" />
     <PackageReference Include="System.Runtime" Version="4.3.1" />    
     <PackageReference Include="Microsoft.VCRTForwarders.140" Version="1.0.7" />
     <PackageReference Include="System.Data.OleDb" Version="6.0.0" />