Merge pull request #2447 from AvaloniaUI/fixes/2388-reshow-window

Throw an exception when trying to re-show a closed window.

src/Avalonia.Controls/Window.cs

@@ -371,8 +371,16 @@ namespace Avalonia.Controls
         /// <summary>
         /// Shows the window.
         /// </summary>
+        /// <exception cref="InvalidOperationException">
+        /// The window has already been closed.
+        /// </exception>
         public override void Show()
         {
+            if (PlatformImpl == null)
+            {
+                throw new InvalidOperationException("Cannot re-show a closed window.");
+            }
+
             if (IsVisible)
             {
                 return;
@@ -397,6 +405,9 @@ namespace Avalonia.Controls
         /// Shows the window as a dialog.
         /// </summary>
         /// <param name="owner">The dialog's owner window.</param>
+        /// <exception cref="InvalidOperationException">
+        /// The window has already been closed.
+        /// </exception>
         /// <returns>
         /// A task that can be used to track the lifetime of the dialog.
         /// </returns>

tests/Avalonia.Controls.UnitTests/WindowTests.cs

@@ -292,6 +292,51 @@ namespace Avalonia.Controls.UnitTests
             }
         }
 
+        [Fact]
+        public void Calling_Show_On_Closed_Window_Should_Throw()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var windowImpl = Mock.Of<IWindowImpl>(x => x.Scaling == 1);
+                var target = new Window(windowImpl);
+
+                target.Show();
+                target.Close();
+
+                var openedRaised = false;
+                target.Opened += (s, e) => openedRaised = true;
+
+                var ex = Assert.Throws<InvalidOperationException>(() => target.Show());
+                Assert.Equal("Cannot re-show a closed window.", ex.Message);
+                Assert.False(openedRaised);
+            }
+        }
+
+        [Fact]
+        public async Task Calling_ShowDialog_On_Closed_Window_Should_Throw()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var parent = new Mock<IWindowImpl>();
+                var windowImpl = new Mock<IWindowImpl>();
+                windowImpl.SetupProperty(x => x.Closed);
+                windowImpl.Setup(x => x.Scaling).Returns(1);
+
+                var target = new Window(windowImpl.Object);
+                var task = target.ShowDialog<bool>(parent.Object);
+
+                windowImpl.Object.Closed();
+                await task;
+
+                var openedRaised = false;
+                target.Opened += (s, e) => openedRaised = true;
+
+                var ex = await Assert.ThrowsAsync<InvalidOperationException>(() => target.ShowDialog<bool>(parent.Object));
+                Assert.Equal("Cannot re-show a closed window.", ex.Message);
+                Assert.False(openedRaised);
+            }
+        }
+
         [Fact]
         public void Window_Should_Be_Centered_When_WindowStartupLocation_Is_CenterScreen()
         {