Blazor EditForm Validation not working when using Child Component

Question

I have a Blazor component called EditOffice. It looks as follows:

<EditForm Model="@Office" OnValidSubmit="@HandleValidSubmit">

    <DataAnnotationsValidator />
    <ValidationSummary />

    <InputTextRow Label="Name" @bind-Value="@Office.Name" Placeholder="Enter name" />
    <InputTextRow Label="ABN" @bind-Value="@Office.ABN" Placeholder="Enter ABN" />
...
    <button type="submit" class="btn btn-primary edit-btn">Save office</button>
</EditForm>

I created child components called InputTextRow in an attempt to Tidy my code. They look as follows:

<div class="form-group row">
    <label for="@Id" class="col-sm-3">@Label: </label>
    <InputText id="@Id" @oninput="OnValueChanged" @bind-Value="@Value" class="form-control col-sm-8" placeholder="@Placeholder"></InputText>
    <ValidationMessage class="offset-sm-3 col-sm-8" For="@(() => Value)" />
</div>

@code {

    public string Id => Label.ToLower().Replace(" ", "");

    [Parameter]
    public string Label { get; set; }

    [Parameter]
    public string Value { get; set; }

    [Parameter]
    public string Placeholder { get; set; }

    [Parameter] public EventCallback<string> ValueChanged { get; set; }

    Task OnValueChanged(ChangeEventArgs e)
    {
        Value = e.Value.ToString();
        return ValueChanged.InvokeAsync(Value);
    }
}

The ValidationMessage doesn't work when in my child component. Any idea why?

Answer 1

In case you would like to use FluentValidations you just need to update your InputTextRow.razor like this:

<div class="form-group row">
    <label for="@Id" class="col-sm-3">@Label: </label>
    <InputText id="@Id" @oninput="OnValueChanged" @bind-Value="@Value" class="form-control col-sm-8" placeholder="@Placeholder"></InputText>
    <ValidationMessage class="offset-sm-3 col-sm-8" For="ValueExpression" />
</div>

@code {
    [Parameter] public string Label { get; set; }
    [Parameter] public string Value { get; set; }
    [Parameter] public EventCallback<string> ValueChanged { get; set; }
    [Parameter] public Expression<Func<string>> ValueExpression { get; set; } = default!;
    [Parameter] public string Placeholder { get; set; }

    [CascadingParameter] public EditContext? EditContext { get; set; }

    public string Id => Label.ToLower().Replace(" ", "");

    Task OnValueChanged(ChangeEventArgs e)
    {
        Value = e.Value.ToString();
        return ValueChanged.InvokeAsync(Value);
    }
}

So 3 changes were made:

• ValueExpression parameter was added. This parameter is filled when you bind a property to it. You need it as input to ValidationMessage
• added EditContext as CascadingParameter. This parameter is automatically filled when your component is in the EditForm
• ValueExpression is now as argument inside ValidationMessage's For argument

---

If you would like to have a condition checking if there is a ValidationMessage available, you can check it like:

private bool _hasValidationMessages => EditContext is null || ValueExpression is null
    ? false
    : EditContext.GetValidationMessages(FieldIdentifier.Create(ValueExpression)).Any();

Answer 2

I know I'm a little late but here is my answer :)

So there is better solution right now.

TL:DR Solution for lazy ones

Be advised - it's experimental, but package is already in release candidate so no worries I guess.

Use Microsoft.AspNetCore.Components.DataAnnotations.Validation package and <ObjectGraphDataAnnotationsValidator /> instead of <DataAnnotationsValidator /> and use this thingy:

using System.ComponentModel.DataAnnotations;

public class YourComplexModel
{
    // other properties

    [ValidateComplexType] // <--life saver
    public ChildModel ChildModel { get; set; } = new ChildModel();
}

Fragment from MS Docs

Link Microsoft Docs:

Blazor provides support for validating form input using data annotations with the built-in DataAnnotationsValidator. However, the DataAnnotationsValidator only validates top-level properties of the model bound to the form that aren't collection- or complex-type properties.

To validate the bound model's entire object graph, including collection- and complex-type properties, use the ObjectGraphDataAnnotationsValidator provided by the experimental Microsoft.AspNetCore.Components.DataAnnotations.Validation package:

<EditForm Model="@model" OnValidSubmit="@HandleValidSubmit">
    <ObjectGraphDataAnnotationsValidator />
    ...
</EditForm>

Annotate model properties with [ValidateComplexType]. In the following model classes, the ShipDescription class contains additional data annotations to validate when the model is bound to the form:

Starship.cs:

using System;
using System.ComponentModel.DataAnnotations;

public class Starship
{
    ...

    [ValidateComplexType]
    public ShipDescription ShipDescription { get; set; } = 
        new ShipDescription();

    ...
}

ShipDescription.cs:

using System;
using System.ComponentModel.DataAnnotations;

public class ShipDescription
{
    [Required]
    [StringLength(40, ErrorMessage = "Description too long (40 char).")]
    public string ShortDescription { get; set; }

    [Required]
    [StringLength(240, ErrorMessage = "Description too long (240 char).")]
    public string LongDescription { get; set; }
}

Answer 3

I am having exactly the same issue. My code is very similar to yours. My child component do validate, but the validation error message is not displayed.

I do use this extension method:

using System;
using Microsoft.AspNetCore.Components.Forms;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;

namespace TimeRecording.Extensions
{
    public static class EditContextExtensions
    {
        static PropertyInfo IsModifiedProperty;
        static MethodInfo GetFieldStateMethod;

        /// <summary>
        /// Validates an entire object tree
        /// </summary>
        /// <param name="editContext">The EditContext to validate the Model of</param>
        /// <returns>True if valid, otherwise false</returns>
        public static bool ValidateObjectTree(this EditContext editContext)
        {
            var validatedObjects = new HashSet<object>();
            ValidateObject(editContext, editContext.Model, validatedObjects);
            editContext.NotifyValidationStateChanged();
            return !editContext.GetValidationMessages().Any();
        }

        public static void ValidateProperty(this EditContext editContext, FieldIdentifier fieldIdentifier)
        {
            if (fieldIdentifier.Model == null)
                return;

            var propertyInfo = fieldIdentifier.Model.GetType().GetProperty(
                fieldIdentifier.FieldName,
                BindingFlags.Public | BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Static);

            var validatedObjects = new HashSet<object>();
            ValidateProperty(editContext, fieldIdentifier.Model, propertyInfo, validatedObjects);
        }

        private static void ValidateObject(
            EditContext editContext,
            object instance,
            HashSet<object> validatedObjects)
        {
            if (instance == null)
                return;

            if (validatedObjects.Contains(instance))
                return;

            if (instance is IEnumerable && !(instance is string))
            {
                foreach (object value in (IEnumerable)instance)
                    ValidateObject(editContext, value, validatedObjects);
                return;
            }

            if (instance.GetType().Assembly == typeof(string).Assembly)
                return;

            validatedObjects.Add(instance);

            var properties = instance.GetType().GetProperties(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
            foreach (PropertyInfo property in properties)
                ValidateProperty(editContext, instance, property, validatedObjects);
        }

        private static void ValidateProperty(
            EditContext editContext,
            object instance,
            PropertyInfo property,
            HashSet<object> validatedObjects)
        {
            NotifyPropertyChanged(editContext, instance, property.Name);

            object value = property.GetValue(instance);
            ValidateObject(editContext, value, validatedObjects);
        }

        private static void NotifyPropertyChanged(
            EditContext editContext,
            object instance,
            string propertyName)
        {
            if (GetFieldStateMethod == null)
            {
                GetFieldStateMethod = editContext.GetType().GetMethod(
                    "GetFieldState",
                    BindingFlags.NonPublic | BindingFlags.Instance);
            }

            var fieldIdentifier = new FieldIdentifier(instance, propertyName);
            object fieldState = GetFieldStateMethod.Invoke(editContext, new object[] { fieldIdentifier, true });

            if (IsModifiedProperty == null)
            {
                IsModifiedProperty = fieldState.GetType().GetProperty(
                    "IsModified",
                    BindingFlags.Public | BindingFlags.Instance);
            }

            object originalIsModified = IsModifiedProperty.GetValue(fieldState);
            editContext.NotifyFieldChanged(fieldIdentifier);
            IsModifiedProperty.SetValue(fieldState, originalIsModified);
        }

    }
}