implement visible changed and tooltip.

samples/ControlCatalog/App.xaml

@@ -1,6 +1,17 @@
 <Application xmlns="https://github.com/avaloniaui"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              x:Class="ControlCatalog.App">
+  <TrayIcon.TrayIcons>
+    <TrayIcons>
+      <TrayIcon Icon="/Assets/test_icon.ico" ToolTipText="Avalonia Tray Icon ToolTip">
+        <NativeMenu.Menu>
+          <NativeMenu>
+            <NativeMenuItem Header="About" />
+          </NativeMenu>
+        </NativeMenu.Menu>
+      </TrayIcon>
+    </TrayIcons>
+  </TrayIcon.TrayIcons>
   <Application.Styles>
     <Style Selector="TextBlock.h1">
       <Setter Property="FontSize" Value="16" />

samples/ControlCatalog/App.xaml.cs

@@ -93,8 +93,6 @@ namespace ControlCatalog
             Styles.Insert(0, FluentLight);
 
             AvaloniaXamlLoader.Load(this);
-
-            
         }
 
         public override void OnFrameworkInitializationCompleted()
@@ -102,14 +100,6 @@ namespace ControlCatalog
             if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktopLifetime)
             {
                 desktopLifetime.MainWindow = new MainWindow();
-
-                var trayIcon1 = new TrayIcon();
-
-                trayIcon1.Icon = desktopLifetime.MainWindow.Icon;
-
-                var trayIcon2 = new TrayIcon();
-
-                trayIcon2.Icon = desktopLifetime.MainWindow.Icon;
             }
             else if (ApplicationLifetime is ISingleViewApplicationLifetime singleViewLifetime)
                 singleViewLifetime.MainView = new MainView();

src/Avalonia.Controls/Platform/ITrayIconImpl.cs

@@ -1,4 +1,7 @@
 using System;
+using Avalonia.Controls;
+
+#nullable enable
 
 namespace Avalonia.Platform
 {
@@ -7,7 +10,7 @@ namespace Avalonia.Platform
         /// <summary>
         /// Sets the icon of this tray icon.
         /// </summary>
-        void SetIcon(IWindowIconImpl icon);
+        void SetIcon(IWindowIconImpl? icon);
 
         /// <summary>
         /// Sets the icon of this tray icon.

src/Avalonia.Controls/TrayIcon.cs

@@ -1,4 +1,6 @@
 using System;
+using System.Collections.Generic;
+using Avalonia.Collections;
 using Avalonia.Controls.Platform;
 using Avalonia.Platform;
 
@@ -6,6 +8,10 @@ using Avalonia.Platform;
 
 namespace Avalonia.Controls
 {
+    public sealed class TrayIcons : AvaloniaList<TrayIcon>
+    {
+    }
+
     public class TrayIcon : AvaloniaObject, IDataContextProvider
     {
         private readonly ITrayIconImpl _impl;
@@ -13,13 +19,50 @@ namespace Avalonia.Controls
         private TrayIcon(ITrayIconImpl impl)
         {
             _impl = impl;
+
+            _impl.SetIsVisible(IsVisible);
         }
 
         public TrayIcon () : this(PlatformManager.CreateTrayIcon())
         {
+        }
+
+        static TrayIcon ()
+        {
+            TrayIconsProperty.Changed.Subscribe(args =>
+            {
+                if (args.Sender is Application application)
+                {
+                    if(args.OldValue.Value != null)
+                    {
+                        RemoveIcons(args.OldValue.Value);
+                    }
+
+                    if(args.NewValue.Value != null)
+                    {
+                        args.NewValue.Value.CollectionChanged += Icons_CollectionChanged;
+                    }
+                }
+            });
+        }
+
+        private static void Icons_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
+        {
             
         }
 
+        private static void RemoveIcons (IEnumerable<TrayIcon> icons)
+        {
+            foreach(var icon in icons)
+            {
+                icon.Remove();
+            }
+        }
+
+
+        public static readonly AttachedProperty<TrayIcons> TrayIconsProperty
+            = AvaloniaProperty.RegisterAttached<TrayIcon, Application, TrayIcons>("TrayIcons");
+
         /// <summary>
         /// Defines the <see cref="DataContext"/> property.
         /// </summary>
@@ -42,6 +85,10 @@ namespace Avalonia.Controls
         public static readonly StyledProperty<bool> IsVisibleProperty =
             Visual.IsVisibleProperty.AddOwner<TrayIcon>();
 
+        public static void SetTrayIcons(AvaloniaObject o, TrayIcons trayIcons) => o.SetValue(TrayIconsProperty, trayIcons);
+
+        public static TrayIcons GetTrayIcons(AvaloniaObject o) => o.GetValue(TrayIconsProperty);
+
         /// <summary>
         /// Removes the notify icon from the taskbar notification area.
         /// </summary>
@@ -102,6 +149,14 @@ namespace Avalonia.Controls
             {
                 _impl.SetIcon(Icon.PlatformImpl);
             }
+            else if (change.Property == IsVisibleProperty)
+            {
+                _impl.SetIsVisible(change.NewValue.GetValueOrDefault<bool>());
+            }
+            else if (change.Property == ToolTipTextProperty)
+            {
+                _impl.SetToolTipText(change.NewValue.GetValueOrDefault<string?>());
+            }
         }
     }
 }

src/Windows/Avalonia.Win32/TrayIconImpl.cs

@@ -10,6 +10,8 @@ using Avalonia.Threading;
 using Avalonia.Win32.Interop;
 using static Avalonia.Win32.Interop.UnmanagedMethods;
 
+#nullable enable
+
 namespace Avalonia.Win32
 {
     public class TrayIconImpl : ITrayIconImpl
@@ -17,7 +19,8 @@ namespace Avalonia.Win32
         private readonly int _uniqueId = 0;
         private static int _nextUniqueId = 0;
         private bool _iconAdded;
-        private IconImpl _icon;
+        private IconImpl? _icon;
+        private string? _tooltipText;
 
         private static Dictionary<int, TrayIconImpl> s_trayIcons = new Dictionary<int, TrayIconImpl>();
 
@@ -34,8 +37,6 @@ namespace Avalonia.Win32
             _uniqueId = ++_nextUniqueId;
 
             s_trayIcons.Add(_uniqueId, this);
-
-            UpdateIcon();
         }
 
 
@@ -44,7 +45,7 @@ namespace Avalonia.Win32
             UpdateIcon(false);
         }
 
-        public void SetIcon(IWindowIconImpl icon)
+        public void SetIcon(IWindowIconImpl? icon)
         {
             _icon = icon as IconImpl;
             UpdateIcon();
@@ -52,15 +53,13 @@ namespace Avalonia.Win32
 
         public void SetIsVisible(bool visible)
         {
-            if (visible)
-            {
-
-            }
+            UpdateIcon(!visible);
         }
 
-        public void SetToolTipText(string text)
+        public void SetToolTipText(string? text)
         {
-            throw new NotImplementedException();
+            _tooltipText = text;
+            UpdateIcon(!_iconAdded);
         }
 
 
@@ -73,7 +72,7 @@ namespace Avalonia.Win32
                 uFlags = NIF.TIP | NIF.MESSAGE,
                 uCallbackMessage = (int)CustomWindowsMessage.WM_TRAYMOUSE,
                 hIcon = _icon?.HIcon ?? new IconImpl(new System.Drawing.Bitmap(32, 32)).HIcon,
-                szTip = "Tool tip text here."
+                szTip = _tooltipText ?? ""
             };
 
             if (!remove)