RadzenDataAnnotationValidator: error message not updated when transitioning between invalid states

Fix #2519

Radzen.Blazor.Tests/DataAnnotationValidatorTests.cs

@@ -0,0 +1,81 @@
+using System;
+using System.ComponentModel.DataAnnotations;
+using System.Linq.Expressions;
+using Bunit;
+using Microsoft.AspNetCore.Components;
+using Xunit;
+
+namespace Radzen.Blazor.Tests
+{
+    public class DataAnnotationValidatorTests
+    {
+        class Model
+        {
+            [Required(ErrorMessage = "Name is required.")]
+            [StringLength(15, MinimumLength = 4, ErrorMessage = "Name must be between 4 and 15 characters.")]
+            public string Name { get; set; }
+        }
+
+        private static IRenderedComponent<RadzenTemplateForm<Model>> RenderForm(TestContext ctx, Model model)
+        {
+            return ctx.RenderComponent<RadzenTemplateForm<Model>>(parameters => parameters
+                .Add(p => p.Data, model)
+                .Add(p => p.ChildContent, editContext => builder =>
+                {
+                    Expression<Func<string>> valueExpression = () => model.Name;
+
+                    builder.OpenComponent<RadzenTextBox>(0);
+                    builder.AddAttribute(1, "Name", "Name");
+                    builder.AddAttribute(2, "Value", model.Name);
+                    builder.AddAttribute(3, "ValueChanged", EventCallback.Factory.Create<string>(model, v => model.Name = v));
+                    builder.AddAttribute(4, "ValueExpression", valueExpression);
+                    builder.CloseComponent();
+
+                    builder.OpenComponent<RadzenDataAnnotationValidator>(5);
+                    builder.AddAttribute(6, "Component", "Name");
+                    builder.CloseComponent();
+                }));
+        }
+
+        [Fact]
+        public void DataAnnotationValidator_Updates_Message_When_Transitioning_Between_Invalid_States()
+        {
+            using var ctx = new TestContext();
+            var model = new Model();
+
+            var form = RenderForm(ctx, model);
+
+            // Trigger validation with empty value → [Required] fails.
+            form.InvokeAsync(() => form.Instance.EditContext.Validate());
+
+            Assert.Contains("Name is required.", form.Markup);
+            Assert.DoesNotContain("Name must be between 4 and 15 characters.", form.Markup);
+
+            // Change value to a single character → [Required] passes, [StringLength] fails.
+            // IsValid remains false, but Text should change and view should re-render.
+            model.Name = "a";
+            form.InvokeAsync(() => form.Instance.EditContext.Validate());
+
+            Assert.Contains("Name must be between 4 and 15 characters.", form.Markup);
+            Assert.DoesNotContain("Name is required.", form.Markup);
+        }
+
+        [Fact]
+        public void DataAnnotationValidator_Clears_Message_When_Value_Becomes_Valid()
+        {
+            using var ctx = new TestContext();
+            var model = new Model();
+
+            var form = RenderForm(ctx, model);
+
+            form.InvokeAsync(() => form.Instance.EditContext.Validate());
+            Assert.Contains("Name is required.", form.Markup);
+
+            model.Name = "valid name";
+            form.InvokeAsync(() => form.Instance.EditContext.Validate());
+
+            Assert.DoesNotContain("Name is required.", form.Markup);
+            Assert.DoesNotContain("Name must be between 4 and 15 characters.", form.Markup);
+        }
+    }
+}

Radzen.Blazor/ValidatorBase.cs

@@ -128,6 +128,8 @@ namespace Radzen.Blazor
             if (component.FieldIdentifier.FieldName != null)
             {
                 var previousIsValid = IsValid;
+                var previousText = Text;
+
                 IsValid = Validate(component);
 
                 messages?.Clear(component.FieldIdentifier);
@@ -137,7 +139,7 @@ namespace Radzen.Blazor
                     messages?.Add(component.FieldIdentifier, Text);
                 }
 
-                if (previousIsValid != IsValid)
+                if (previousIsValid != IsValid || (!IsValid && previousText != Text))
                 {
                     EditContext?.NotifyValidationStateChanged();
                 }