From 5580e0f54b107afd3b216966626cdce115e75c37 Mon Sep 17 00:00:00 2001
From: Dan Walmsley <dan@walms.co.uk>
Date: Fri, 28 Aug 2020 11:01:05 +0100
Subject: [PATCH 1/3] add failing unit test.

---
 .../ToolTipTests.cs                           | 29 +++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/tests/Avalonia.Controls.UnitTests/ToolTipTests.cs b/tests/Avalonia.Controls.UnitTests/ToolTipTests.cs
index e52e7a487b..9279e78013 100644
--- a/tests/Avalonia.Controls.UnitTests/ToolTipTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/ToolTipTests.cs
@@ -124,6 +124,35 @@ namespace Avalonia.Controls.UnitTests
                 Assert.True(ToolTip.GetIsOpen(target));
             }
         }
+        
+        [Fact]
+        public void Content_Should_Update_When_Tip_Property_Changes_And_Already_Open()
+        {
+            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));
+                Assert.Equal("Tip", target.GetValue(ToolTip.ToolTipProperty).Content);
+                
+                
+                ToolTip.SetTip(target, "Tip1");
+                Assert.Equal("Tip1", target.GetValue(ToolTip.ToolTipProperty).Content);
+            }
+        }
 
         [Fact]
         public void Should_Open_On_Pointer_Enter_With_Delay()

From 3c369153c25d3b18aaf7e5c6a3852d982097a477 Mon Sep 17 00:00:00 2001
From: Dan Walmsley <dan@walms.co.uk>
Date: Fri, 28 Aug 2020 11:01:48 +0100
Subject: [PATCH 2/3] update tooltip content when already opened and tip
 changes.

---
 src/Avalonia.Controls/ToolTip.cs        | 2 +-
 src/Avalonia.Controls/ToolTipService.cs | 7 +++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/Avalonia.Controls/ToolTip.cs b/src/Avalonia.Controls/ToolTip.cs
index cf0652247f..d56ff5752f 100644
--- a/src/Avalonia.Controls/ToolTip.cs
+++ b/src/Avalonia.Controls/ToolTip.cs
@@ -55,7 +55,7 @@ namespace Avalonia.Controls
         /// <summary>
         /// Stores the current <see cref="ToolTip"/> instance in the control.
         /// </summary>
-        private static readonly AttachedProperty<ToolTip> ToolTipProperty =
+        internal static readonly AttachedProperty<ToolTip> ToolTipProperty =
             AvaloniaProperty.RegisterAttached<ToolTip, Control, ToolTip>("ToolTip");
 
         private IPopupHost _popup;
diff --git a/src/Avalonia.Controls/ToolTipService.cs b/src/Avalonia.Controls/ToolTipService.cs
index e2a0f9e50c..92d2e7cbfe 100644
--- a/src/Avalonia.Controls/ToolTipService.cs
+++ b/src/Avalonia.Controls/ToolTipService.cs
@@ -35,6 +35,13 @@ namespace Avalonia.Controls
                 control.PointerEnter += ControlPointerEnter;
                 control.PointerLeave += ControlPointerLeave;
             }
+
+            if (e.NewValue != e.OldValue && ToolTip.GetIsOpen(control))
+            {
+                var tip = control.GetValue(ToolTip.ToolTipProperty);
+
+                tip.Content = e.NewValue;
+            }
         }
 
         internal void TipOpenChanged(AvaloniaPropertyChangedEventArgs e)

From 03a1eae221cfee2d941f197bd43b142c4f19e491 Mon Sep 17 00:00:00 2001
From: Dan Walmsley <dan@walms.co.uk>
Date: Fri, 28 Aug 2020 18:10:25 +0100
Subject: [PATCH 3/3] just check newvalue isnt tooltip.

---
 src/Avalonia.Controls/ToolTipService.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Avalonia.Controls/ToolTipService.cs b/src/Avalonia.Controls/ToolTipService.cs
index 92d2e7cbfe..341ab2fe81 100644
--- a/src/Avalonia.Controls/ToolTipService.cs
+++ b/src/Avalonia.Controls/ToolTipService.cs
@@ -36,7 +36,7 @@ namespace Avalonia.Controls
                 control.PointerLeave += ControlPointerLeave;
             }
 
-            if (e.NewValue != e.OldValue && ToolTip.GetIsOpen(control))
+            if (ToolTip.GetIsOpen(control) && e.NewValue != e.OldValue && !(e.NewValue is ToolTip))
             {
                 var tip = control.GetValue(ToolTip.ToolTipProperty);