Initial

samples/ControlCatalog.Desktop/Program.cs

@@ -4,7 +4,6 @@ using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Logging.Serilog;
 using Avalonia.Platform;
-using Serilog;
 
 namespace ControlCatalog
 {
@@ -15,7 +14,12 @@ namespace ControlCatalog
         {
             // TODO: Make this work with GTK/Skia/Cairo depending on command-line args
             // again.
-            BuildAvaloniaApp().Start<MainWindow>();
+            BuildAvaloniaApp().Start(AppMain, args);
+        }
+
+        private static void AppMain(Application app, string[] args)
+        {
+            app.Run();
         }
 
         /// <summary>

samples/ControlCatalog.NetCore/Program.cs

@@ -36,7 +36,7 @@ namespace ControlCatalog.NetCore
 
         static void AppMain(Application app, string[] args)
         {
-            app.Run(new MainWindow());
+            app.Run();           
         }
 
         /// <summary>

samples/ControlCatalog/App.xaml.cs

@@ -9,5 +9,14 @@ namespace ControlCatalog
         {
             AvaloniaXamlLoader.Load(this);
         }
+
+        protected override void OnStartup()
+        {
+            base.OnStartup();
+
+            var mainWindow = new MainWindow();
+
+            mainWindow.Show();
+        }
     }
 }

src/Avalonia.Controls/AppBuilderBase.cs

@@ -147,13 +147,20 @@ namespace Avalonia.Controls
 
         public delegate void AppMainDelegate(Application app, string[] args);
 
+        public void Start()
+        {
+            Setup();
+            BeforeStartCallback(Self);
+            Instance.Run();
+        }
+
         public void Start(AppMainDelegate main, string[] args)
         {
             Setup();
             BeforeStartCallback(Self);
             main(Instance, args);
         }
-        
+
         /// <summary>
         /// Sets up the platform-specific services for the application, but does not run it.
         /// </summary>
@@ -219,13 +226,13 @@ namespace Avalonia.Controls
         /// <summary>
         /// Sets the shutdown mode of the application.
         /// </summary>
-        /// <param name="exitMode">The shutdown mode.</param>
+        /// <param name="shutdownMode">The shutdown mode.</param>
         /// <returns></returns>
-        public TAppBuilder SetExitMode(ExitMode exitMode)
+        public TAppBuilder SetExitMode(ShutdownMode shutdownMode)
         {
-            Instance.ExitMode = exitMode;
+            Instance.ShutdownMode = shutdownMode;
             return Self;
-        }      
+        }
 
         protected virtual bool CheckSetup => true;
 

src/Avalonia.Controls/Application.cs

@@ -52,10 +52,14 @@ namespace Avalonia
         public Application()
         {
             Windows = new WindowCollection(this);
-
-            OnExit += OnExiting;
         }
 
+        /// <inheritdoc/>
+        public event EventHandler Startup;
+
+        /// <inheritdoc/>
+        public event EventHandler Exit;
+
         /// <inheritdoc/>
         public event EventHandler<ResourcesChangedEventArgs> ResourcesChanged;
 
@@ -164,14 +168,14 @@ namespace Avalonia
         IResourceNode IResourceNode.ResourceParent => null;
 
         /// <summary>
-        /// Gets or sets the <see cref="ExitMode"/>. This property indicates whether the application exits explicitly or implicitly. 
-        /// If <see cref="ExitMode"/> is set to OnExplicitExit the application is only closes if Exit is called.
+        /// Gets or sets the <see cref="ShutdownMode"/>. This property indicates whether the application is shutdown explicitly or implicitly. 
+        /// If <see cref="ShutdownMode"/> is set to OnExplicitShutdown the application is only closes if Shutdown is called.
         /// The default is OnLastWindowClose
         /// </summary>
         /// <value>
         /// The shutdown mode.
         /// </value>
-        public ExitMode ExitMode { get; set; }
+        public ShutdownMode ShutdownMode { get; set; }
 
         /// <summary>
         /// Gets or sets the main window of the application.
@@ -190,12 +194,12 @@ namespace Avalonia
         public WindowCollection Windows { get; }
 
         /// <summary>
-        /// Gets or sets a value indicating whether this instance is existing.
+        /// Gets or sets a value indicating whether this instance is shutting down.
         /// </summary>
         /// <value>
-        ///   <c>true</c> if this instance is existing; otherwise, <c>false</c>.
+        ///   <c>true</c> if this instance is shutting down; otherwise, <c>false</c>.
         /// </value>
-        internal bool IsExiting { get; set; }
+        internal bool IsShuttingDown { get; set; }
 
         /// <summary>
         /// Initializes the application by loading XAML etc.
@@ -204,6 +208,35 @@ namespace Avalonia
         {
         }
 
+        public void Run()
+        {
+            if (_mainLoopCancellationTokenSource != null)
+            {
+                throw new Exception("Run should only called once");
+            }
+
+            _mainLoopCancellationTokenSource = new CancellationTokenSource();
+
+            Dispatcher.UIThread.Post(OnStartup, DispatcherPriority.Send);
+
+            Run(_mainLoopCancellationTokenSource.Token);
+        }
+
+        /// <summary>
+        /// Runs the application's main loop until the <see cref="CancellationToken"/> is canceled.
+        /// </summary>
+        /// <param name="token">The token to track</param>
+        public void Run(CancellationToken token)
+        {
+            Dispatcher.UIThread.MainLoop(token);
+
+            // Make sure we call OnExit in case an error happened and OnExit() wasn't called explicitly
+            if (!IsShuttingDown)
+            {
+                OnExit();
+            }
+        }
+
         /// <summary>
         /// Runs the application's main loop until the <see cref="ICloseable"/> is closed.
         /// </summary>
@@ -215,17 +248,11 @@ namespace Avalonia
                 throw new Exception("Run should only called once");
             }
 
-            closable.Closed += (s, e) => Exit();
+            closable.Closed += (s, e) => OnExit();
 
             _mainLoopCancellationTokenSource = new CancellationTokenSource();
 
-            Dispatcher.UIThread.MainLoop(_mainLoopCancellationTokenSource.Token);
-
-            // Make sure we call OnExit in case an error happened and Exit() wasn't called explicitly
-            if (!IsExiting)
-            {
-                OnExit?.Invoke(this, EventArgs.Empty);
-            }
+            Run(_mainLoopCancellationTokenSource.Token);
         }
 
         /// <summary>
@@ -252,46 +279,31 @@ namespace Avalonia
                 {
                     mainWindow.Show();
                 }
-
-                MainWindow = mainWindow;
-            }           
-
-            Dispatcher.UIThread.MainLoop(_mainLoopCancellationTokenSource.Token);
-
-            // Make sure we call OnExit in case an error happened and Exit() wasn't called explicitly
-            if (!IsExiting)
-            {
-                OnExit?.Invoke(this, EventArgs.Empty);
             }
+
+            Run(_mainLoopCancellationTokenSource.Token);
         }
 
-        /// <summary>
-        /// Runs the application's main loop until the <see cref="CancellationToken"/> is canceled.
-        /// </summary>
-        /// <param name="token">The token to track</param>
-        public void Run(CancellationToken token)
+        protected virtual void OnStartup()
         {
-            Dispatcher.UIThread.MainLoop(token);
+            Startup?.Invoke(this, EventArgs.Empty);
+        }
 
-            // Make sure we call OnExit in case an error happened and Exit() wasn't called explicitly
-            if (!IsExiting)
-            {
-                OnExit?.Invoke(this, EventArgs.Empty);
-            }
+        protected virtual void OnExit()
+        {
+            Exit?.Invoke(this, EventArgs.Empty);
         }
 
-        /// <summary>
-        /// Exits the application
-        /// </summary>
-        public void Exit()
+        /// <inheritdoc/>
+        public void Shutdown()
         {
-            IsExiting = true;
+            IsShuttingDown = true;
 
             Windows.Clear();
 
-            OnExit?.Invoke(this, EventArgs.Empty);
-
             _mainLoopCancellationTokenSource?.Cancel();
+
+            OnExit();
         }
 
         /// <inheritdoc/>
@@ -302,19 +314,7 @@ namespace Avalonia
                    Styles.TryGetResource(key, out value);
         }
 
-        /// <summary>
-        /// Sent when the application is exiting.
-        /// </summary>
-        public event EventHandler OnExit;
 
-        /// <summary>
-        /// Called when the application is exiting.
-        /// </summary>
-        /// <param name="sender"></param>
-        /// <param name="e"></param>
-        protected virtual void OnExiting(object sender, EventArgs e)
-        {
-        }
 
         /// <summary>
         /// Register's the services needed by Avalonia.

src/Avalonia.Controls/IApplicationLifecycle.cs

@@ -7,14 +7,19 @@ namespace Avalonia.Controls
     /// </summary>
     public interface IApplicationLifecycle
     {
+        /// <summary>
+        /// Sent when the application is starting up.
+        /// </summary>
+        event EventHandler Startup;
+
         /// <summary>
         /// Sent when the application is exiting.
         /// </summary>
-        event EventHandler OnExit;
+        event EventHandler Exit;
 
         /// <summary>
         /// Exits the application.
         /// </summary>
-        void Exit();
+        void Shutdown();
     }
 }

src/Avalonia.Controls/ExitMode.cs → src/Avalonia.Controls/ShutdownMode.cs

@@ -6,7 +6,7 @@ namespace Avalonia
     /// <summary>
     /// Enum for ExitMode
     /// </summary>
-    public enum ExitMode
+    public enum ShutdownMode
     {
         /// <summary>
         /// Indicates an implicit call to Application.Exit when the last window closes.
@@ -19,8 +19,8 @@ namespace Avalonia
         OnMainWindowClose,
 
         /// <summary>
-        /// Indicates that the application only exits on an explicit call to Application.Exit.
+        /// Indicates that the application only exits on an explicit call to Application.Shutdown.
         /// </summary>
-        OnExplicitExit
+        OnExplicitShutdown
     }
-}
+}

src/Avalonia.Controls/TopLevel.cs

@@ -124,7 +124,7 @@ namespace Avalonia.Controls
 
             if (_applicationLifecycle != null)
             {
-                _applicationLifecycle.OnExit += OnApplicationExiting;
+                _applicationLifecycle.Exit += OnApplicationExiting;
             }
 
             if (((IStyleHost)this).StylingParent is IResourceProvider applicationResources)
@@ -278,7 +278,7 @@ namespace Avalonia.Controls
             Closed?.Invoke(this, EventArgs.Empty);
             Renderer?.Dispose();
             Renderer = null;
-            _applicationLifecycle.OnExit -= OnApplicationExiting;
+            _applicationLifecycle.Exit -= OnApplicationExiting;
         }
 
         /// <summary>

src/Avalonia.Controls/Window.cs

@@ -49,6 +49,8 @@ namespace Avalonia.Controls
     /// </summary>
     public class Window : WindowBase, IStyleable, IFocusScope, ILayoutRoot, INameScope
     {
+        private static bool s_hasAddedFirstWindow;
+
         /// <summary>
         /// Defines the <see cref="SizeToContent"/> property.
         /// </summary>
@@ -250,7 +252,7 @@ namespace Avalonia.Controls
         /// <summary>
         /// Fired before a window is closed.
         /// </summary>
-        public event EventHandler<CancelEventArgs> Closing;
+        public event EventHandler<CancelEventArgs> Closing;      
 
         private static void AddWindow(Window window)
         {
@@ -260,6 +262,18 @@ namespace Avalonia.Controls
             }
 
             Application.Current.Windows.Add(window);
+
+            if (s_hasAddedFirstWindow)
+            {
+                return;
+            }
+
+            s_hasAddedFirstWindow = true;
+
+            if (Application.Current.MainWindow == null)
+            {
+                Application.Current.MainWindow = window;
+            }
         }
 
         private static void RemoveWindow(Window window)
@@ -428,7 +442,7 @@ namespace Avalonia.Controls
         /// </returns>
         public Task<TResult> ShowDialog<TResult>(IWindowImpl owner)
         {
-            if(owner == null)
+            if (owner == null)
                 throw new ArgumentNullException(nameof(owner));
 
             if (IsVisible)

src/Avalonia.Controls/WindowCollection.cs

@@ -107,24 +107,24 @@ namespace Avalonia
                 return;
             }
 
-            if (_application.IsExiting)
+            if (_application.IsShuttingDown)
             {
                 return;
             }
 
-            switch (_application.ExitMode)
+            switch (_application.ShutdownMode)
             {
-                case ExitMode.OnLastWindowClose:
+                case ShutdownMode.OnLastWindowClose:
                     if (Count == 0)
                     {
-                        _application.Exit();
+                        _application.Shutdown();
                     }
 
                     break;
-                case ExitMode.OnMainWindowClose:
+                case ShutdownMode.OnMainWindowClose:
                     if (window == _application.MainWindow)
                     {
-                        _application.Exit();
+                        _application.Shutdown();
                     }
 
                     break;                   

tests/Avalonia.Controls.UnitTests/ApplicationTests.cs

@@ -15,7 +15,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                Application.Current.ExitMode = ExitMode.OnMainWindowClose;
+                Application.Current.ShutdownMode = ShutdownMode.OnMainWindowClose;
 
                 var mainWindow = new Window();
 
@@ -29,7 +29,7 @@ namespace Avalonia.Controls.UnitTests
 
                 mainWindow.Close();
 
-                Assert.True(Application.Current.IsExiting);
+                Assert.True(Application.Current.IsShuttingDown);
             }
         }
 
@@ -38,7 +38,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                Application.Current.ExitMode = ExitMode.OnLastWindowClose;
+                Application.Current.ShutdownMode = ShutdownMode.OnLastWindowClose;
 
                 var windowA = new Window();
 
@@ -50,11 +50,11 @@ namespace Avalonia.Controls.UnitTests
 
                 windowA.Close();
 
-                Assert.False(Application.Current.IsExiting);
+                Assert.False(Application.Current.IsShuttingDown);
 
                 windowB.Close();
 
-                Assert.True(Application.Current.IsExiting);
+                Assert.True(Application.Current.IsShuttingDown);
             }
         }
 
@@ -63,7 +63,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                Application.Current.ExitMode = ExitMode.OnExplicitExit;
+                Application.Current.ShutdownMode = ShutdownMode.OnExplicitShutdown;
 
                 var windowA = new Window();
 
@@ -75,15 +75,15 @@ namespace Avalonia.Controls.UnitTests
 
                 windowA.Close();
 
-                Assert.False(Application.Current.IsExiting);
+                Assert.False(Application.Current.IsShuttingDown);
 
                 windowB.Close();
 
-                Assert.False(Application.Current.IsExiting);
+                Assert.False(Application.Current.IsShuttingDown);
 
-                Application.Current.Exit();
+                Application.Current.Shutdown();
 
-                Assert.True(Application.Current.IsExiting);
+                Assert.True(Application.Current.IsShuttingDown);
             }
         }
 
@@ -99,7 +99,7 @@ namespace Avalonia.Controls.UnitTests
                     window.Show();
                 }
 
-                Application.Current.Exit();
+                Application.Current.Shutdown();
 
                 Assert.Empty(Application.Current.Windows);
             }
@@ -129,5 +129,18 @@ namespace Avalonia.Controls.UnitTests
                 Assert.True(raised);
             }
         }
+
+        [Fact]
+        public void Should_Have_MainWindow_After_First_Window_Shown()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {                
+                var mainWindow = new Window();
+
+                mainWindow.Show();            
+
+                Assert.Equal(mainWindow, Application.Current.MainWindow);
+            }
+        }
     }
 }

tests/Avalonia.Controls.UnitTests/TopLevelTests.cs

@@ -215,7 +215,7 @@ namespace Avalonia.Controls.UnitTests
                 var impl = new Mock<ITopLevelImpl>();
                 impl.SetupAllProperties();
                 var target = new TestTopLevel(impl.Object);
-                UnitTestApplication.Current.Exit();
+                UnitTestApplication.Current.Shutdown();
                 Assert.True(target.IsClosed);
             }
         }