From 21a38e81c4e404a3694b139ff3888dcd01e3e1fa Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ond=C5=99ej=20Su=C5=A1ovsk=C3=BD?= <o.susovsky@gmail.com>
Date: Tue, 19 Aug 2025 12:08:25 +0200
Subject: [PATCH] Fix validation error not being cleared on valid input
 (#19477)

* Add failing test for binding error not being cleared, when bound value does not change

* Fix clearing binding error
---
 .../Data/Core/BindingExpression.cs            |  5 +++--
 .../BindingExpressionTests.DataValidation.cs  | 20 +++++++++++++++++++
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/src/Avalonia.Base/Data/Core/BindingExpression.cs b/src/Avalonia.Base/Data/Core/BindingExpression.cs
index 46e4af7e3c..ca29dd6ffa 100644
--- a/src/Avalonia.Base/Data/Core/BindingExpression.cs
+++ b/src/Avalonia.Base/Data/Core/BindingExpression.cs
@@ -355,8 +355,9 @@ internal partial class BindingExpression : UntypedBindingExpressionBase, IDescri
             }
         }
 
-        // Don't set the value if it's unchanged.
-        if (TypeUtilities.IdentityEquals(LeafNode.Value, value, type))
+        // Don't set the value if it's unchanged. If there is a binding error, we still have to set the value
+        // in order to clear the error.
+        if (TypeUtilities.IdentityEquals(LeafNode.Value, value, type) && ErrorType == BindingErrorType.None)
             return true;
 
         try
diff --git a/tests/Avalonia.Base.UnitTests/Data/Core/BindingExpressionTests.DataValidation.cs b/tests/Avalonia.Base.UnitTests/Data/Core/BindingExpressionTests.DataValidation.cs
index 8e1865f209..2a57026576 100644
--- a/tests/Avalonia.Base.UnitTests/Data/Core/BindingExpressionTests.DataValidation.cs
+++ b/tests/Avalonia.Base.UnitTests/Data/Core/BindingExpressionTests.DataValidation.cs
@@ -305,6 +305,26 @@ public partial class BindingExpressionTests
             BindingErrorType.DataValidationError);
     }
 
+    [Fact]
+    public void Setting_Valid_Value_Should_Clear_Binding_Error()
+    {
+        var data = new ViewModel { DoubleValue = 5.6 };
+        var target = CreateTargetWithSource(
+            data,
+            o => o.DoubleValue,
+            enableDataValidation: true,
+            mode: BindingMode.TwoWay,
+            targetProperty: TargetClass.StringProperty);
+
+        target.String = "5.6";
+        target.String = "5.6a";
+        target.String = "5.6";
+
+        AssertNoError(target, TargetClass.StringProperty);
+
+        GC.KeepAlive(data);
+    }
+
     public class ExceptionViewModel : NotifyingBase
     {
         private int _mustBePositive;