Placeholder for validation error messages

Source/ReactiveProperty.NETStandard/ReactivePropertyExtensions.cs

@@ -23,10 +23,12 @@ public static ReactiveProperty<T> SetValidateAttribute<T>(this ReactiveProperty<
         {
             var memberExpression = (MemberExpression)selfSelector.Body;
             var propertyInfo = (PropertyInfo)memberExpression.Member;
+            var display = propertyInfo.GetCustomAttribute<DisplayAttribute>();
             var attrs = propertyInfo.GetCustomAttributes<ValidationAttribute>().ToArray();
             var context = new ValidationContext(self)
             {
-                MemberName = nameof(ReactiveProperty<T>.Value)
+                DisplayName = display?.GetName() ?? propertyInfo.Name,
+                MemberName = nameof(ReactiveProperty<T>.Value),
             };
 
             if (attrs.Length != 0)

Test/ReactiveProperty.Tests/ReactiveProperty.Tests.csproj

@@ -31,4 +31,17 @@
     <Reference Include="PresentationCore" />
     <Reference Include="PresentationFramework" />
   </ItemGroup>
+  <ItemGroup>
+    <Compile Update="Strings\Resource.Designer.cs">
+      <DesignTime>True</DesignTime>
+      <AutoGen>True</AutoGen>
+      <DependentUpon>Resource.resx</DependentUpon>
+    </Compile>
+  </ItemGroup>
+  <ItemGroup>
+    <EmbeddedResource Update="Strings\Resource.resx">
+      <Generator>PublicResXFileCodeGenerator</Generator>
+      <LastGenOutput>Resource.Designer.cs</LastGenOutput>
+    </EmbeddedResource>
+  </ItemGroup>
 </Project>

Test/ReactiveProperty.Tests/ReactivePropertyValidationTest.cs

@@ -1,13 +1,15 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using System.ComponentModel;
 using System.ComponentModel.DataAnnotations;
 using System.Linq;
 using System.Reactive.Linq;
 using System.Threading.Tasks;
 using Microsoft.Reactive.Testing;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Reactive.Bindings;
+using ReactiveProperty.Tests.Strings;
 
 namespace ReactiveProperty.Tests
 {
@@ -136,7 +138,7 @@ public async Task AsyncValidation_FailedCase()
             var errorMessage = "error occured!!";
             rprop.Value = "dummy";  //--- push value
             tcs.SetResult(errorMessage);    //--- validation error!
-            await Task.Yield();
+            await Task.Delay(10);
 
             rprop.HasErrors.IsTrue();
             error.IsNotNull();
@@ -237,6 +239,45 @@ public void IgnoreInitErrorAndUpdateValue()
             rp.Value = "";
             rp.HasErrors.IsTrue();
         }
+
+        [TestMethod]
+        public void CustomValidationErrorMessage()
+        {
+            var target = new TestTarget();
+            target.CustomValidationErrorMessageProperty.Value = "";
+            var errorMessage = target
+                .CustomValidationErrorMessageProperty
+                .GetErrors(nameof(TestTarget.CustomValidationErrorMessageProperty))
+                .Cast<string>()
+                .First();
+            errorMessage.Is("Custom validation error message for CustomValidationErrorMessageProperty");
+        }
+
+        [TestMethod]
+        public void CustomValidationErrorMessageWithDisplayName()
+        {
+            var target = new TestTarget();
+            target.CustomValidationErrorMessageWithDisplayNameProperty.Value = "";
+            var errorMessage = target
+                .CustomValidationErrorMessageWithDisplayNameProperty
+                .GetErrors(nameof(TestTarget.CustomValidationErrorMessageWithDisplayNameProperty))
+                .Cast<string>()
+                .First();
+            errorMessage.Is("Custom validation error message for CustomName");
+        }
+
+        [TestMethod]
+        public void CustomValidationErrorMessageWithResource()
+        {
+            var target = new TestTarget();
+            target.CustomValidationErrorMessageWithResourceProperty.Value = "";
+            var errorMessage = target
+                .CustomValidationErrorMessageWithResourceProperty
+                .GetErrors(nameof(TestTarget.CustomValidationErrorMessageWithResourceProperty))
+                .Cast<string>()
+                .First();
+            errorMessage.Is("Oops!? FromResource is required.");
+        }
     }
 
     internal class TestTarget
@@ -249,6 +290,17 @@ internal class TestTarget
 
         public ReactiveProperty<string> TaskValidationTestProperty { get; private set; }
 
+        [Required(ErrorMessage = "Custom validation error message for {0}")]
+        public ReactiveProperty<string> CustomValidationErrorMessageProperty { get; }
+
+        [Required(ErrorMessage = "Custom validation error message for {0}")]
+        [Display(Name = "CustomName")]
+        public ReactiveProperty<string> CustomValidationErrorMessageWithDisplayNameProperty { get; }
+
+        [Required(ErrorMessageResourceType = typeof(Resource), ErrorMessageResourceName = nameof(Resource.ValidationErrorMessage))]
+        [Display(ResourceType = typeof(Resource), Name = nameof(Resource.ValidationTargetPropertyName))]
+        public ReactiveProperty<string> CustomValidationErrorMessageWithResourceProperty { get; }
+
         public TestTarget()
         {
             RequiredProperty = new ReactiveProperty<string>()
@@ -267,6 +319,15 @@ public TestTarget()
                     }
                     return await Task.FromResult((string)null);
                 });
+
+            CustomValidationErrorMessageProperty = new ReactiveProperty<string>()
+                .SetValidateAttribute(() => CustomValidationErrorMessageProperty);
+
+            CustomValidationErrorMessageWithDisplayNameProperty = new ReactiveProperty<string>()
+                .SetValidateAttribute(() => CustomValidationErrorMessageWithDisplayNameProperty);
+
+            CustomValidationErrorMessageWithResourceProperty = new ReactiveProperty<string>()
+                .SetValidateAttribute(() => CustomValidationErrorMessageWithResourceProperty);
         }
     }
 }