Add Plugin API -> VisibiltyChangedEventHandler

Flow.Launcher.Plugin/Interfaces/IPublicAPI.cs

@@ -96,7 +96,12 @@ namespace Flow.Launcher.Plugin
         /// </summary>
         /// <returns></returns>
         bool IsMainWindowVisible();
-        
+
+        /// <summary>
+        /// Invoked when the visibility of the main window has changed
+        /// </summary>
+        event VisibilityChangedEventHandler VisibilityChanged;
+
         /// <summary>
         /// Show message box
         /// </summary>

Flow.Launcher.Plugin/VisibilityChangedEventHandler.cs

@@ -0,0 +1,21 @@
+using System;
+
+namespace Flow.Launcher.Plugin
+{
+    /// <summary>
+    /// A delegate for when the visibility is changed
+    /// </summary>
+    /// <param name="sender"></param>
+    /// <param name="args"></param>
+    public delegate void VisibilityChangedEventHandler(object sender, VisibilityChangedEventArgs args);
+    /// <summary>
+    /// The event args for <see cref="VisibilityChangedEventHandler"/>
+    /// </summary>
+    public class VisibilityChangedEventArgs : EventArgs
+    {
+        /// <summary>
+        /// <see langword="true"/> if the main window has become visible
+        /// </summary>
+        public bool IsVisible { get; init; }
+    }
+}

Flow.Launcher/PublicAPIInstance.cs

@@ -75,6 +75,8 @@ namespace Flow.Launcher
 
         public bool IsMainWindowVisible() => _mainVM.MainWindowVisibilityStatus;
 
+        public event VisibilityChangedEventHandler VisibilityChanged { add => _mainVM.VisibilityChanged += value; remove => _mainVM.VisibilityChanged -= value; }
+
         public void CheckForNewUpdate() => _settingsVM.UpdateApp();
 
         public void SaveAppAllSettings()

Flow.Launcher/ViewModel/MainViewModel.cs

@@ -578,6 +578,8 @@ namespace Flow.Launcher.ViewModel
         // because it is more accurate and reliable representation than using Visibility as a condition check
         public bool MainWindowVisibilityStatus { get; set; } = true;
 
+        public event VisibilityChangedEventHandler VisibilityChanged;
+
         public Visibility SearchIconVisibility { get; set; }
 
         public double MainWindowWidth
@@ -1014,6 +1016,7 @@ namespace Flow.Launcher.ViewModel
                 MainWindowOpacity = 1;
 
                 MainWindowVisibilityStatus = true;
+                VisibilityChanged?.Invoke(this, new VisibilityChangedEventArgs { IsVisible = true });
             });
         }
 
@@ -1048,6 +1051,7 @@ namespace Flow.Launcher.ViewModel
 
             MainWindowVisibilityStatus = false;
             MainWindowVisibility = Visibility.Collapsed;
+            VisibilityChanged?.Invoke(this, new VisibilityChangedEventArgs { IsVisible = false });
         }
 
         /// <summary>