Merge pull request #5297 from AvaloniaUI/fix-tooltip-null-values

Close tooltip on null Tip value

src/Avalonia.Controls/ToolTipService.cs

@@ -38,9 +38,16 @@ namespace Avalonia.Controls
 
             if (ToolTip.GetIsOpen(control) && e.NewValue != e.OldValue && !(e.NewValue is ToolTip))
             {
-                var tip = control.GetValue(ToolTip.ToolTipProperty);
-
-                tip.Content = e.NewValue;
+                if (e.NewValue is null)
+                {
+                    Close(control);
+                }
+                else
+                {
+                    var tip = control.GetValue(ToolTip.ToolTipProperty);
+
+                    tip.Content = e.NewValue;
+                }
             }
         }
 

tests/Avalonia.Controls.UnitTests/ToolTipTests.cs

@@ -270,6 +270,34 @@ namespace Avalonia.Controls.UnitTests
                 Assert.Empty(toolTip.Classes);
             }
         }
+
+        [Fact]
+        public void Should_Close_On_Null_Tip()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var window = new Window();
+
+                var target = new Decorator()
+                {
+                    [ToolTip.TipProperty] = "Tip",
+                    [ToolTip.ShowDelayProperty] = 0
+                };
+
+                window.Content = target;
+
+                window.ApplyTemplate();
+                window.Presenter.ApplyTemplate();
+
+                _mouseHelper.Enter(target);
+
+                Assert.True(ToolTip.GetIsOpen(target));
+
+                target[ToolTip.TipProperty] = null;
+
+                Assert.False(ToolTip.GetIsOpen(target));
+            }
+        }
     }
 
     internal class ToolTipViewModel