I validate my Blazor form input according to this pattern with ValidationMessageStore:

https://docs.microsoft.com/en-us/aspnet/core/blazor/forms-validation?view=aspnetcore-5.0#basic-validation-1

I then output ValidationMessage on each control.

BUT it is a long form so I also want to indicate to the user somewhere close to the submit button that there are some errors that need to be fixed, and that's why we didn't accept the input yet.

I know I can use a ValidationSummary but I don't want to repeat all possible errors, just have a note.

ValidationMessageStore obviously holds all messages in an internal collection, but they are not accessible. Is it possible to somehow check if there are ANY error messages?

CodePudding user response：

Take a look at the ValidationSummary code - the validation message store is available. It's not very complicated, so you should be able to build yourself a similar but simpler component to display what you want.

The code is here: https://github.com/dotnet/aspnetcore/blob/main/src/Components/Web/src/Forms/ValidationSummary.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using System.Collections.Generic;
using Microsoft.AspNetCore.Components.Rendering;

namespace Microsoft.AspNetCore.Components.Forms
{
    // Note: there's no reason why developers strictly need to use this. It's equally valid to
    // put a @foreach(var message in context.GetValidationMessages()) { ... } inside a form.
    // This component is for convenience only, plus it implements a few small perf optimizations.

    /// <summary>
    /// Displays a list of validation messages from a cascaded <see cref="EditContext"/>.
    /// </summary>
    public class ValidationSummary : ComponentBase, IDisposable
    {
        private EditContext? _previousEditContext;
        private readonly EventHandler<ValidationStateChangedEventArgs> _validationStateChangedHandler;

        /// <summary>
        /// Gets or sets the model to produce the list of validation messages for.
        /// When specified, this lists all errors that are associated with the model instance.
        /// </summary>
        [Parameter] public object? Model { get; set; }

        /// <summary>
        /// Gets or sets a collection of additional attributes that will be applied to the created <c>ul</c> element.
        /// </summary>
        [Parameter(CaptureUnmatchedValues = true)] public IReadOnlyDictionary<string, object>? AdditionalAttributes { get; set; }

        [CascadingParameter] EditContext CurrentEditContext { get; set; } = default!;

        /// <summary>`
        /// Constructs an instance of <see cref="ValidationSummary"/>.
        /// </summary>
        public ValidationSummary()
        {
            _validationStateChangedHandler = (sender, eventArgs) => StateHasChanged();
        }

        /// <inheritdoc />
        protected override void OnParametersSet()
        {
            if (CurrentEditContext == null)
            {
                throw new InvalidOperationException($"{nameof(ValidationSummary)} requires a cascading parameter "  
                    $"of type {nameof(EditContext)}. For example, you can use {nameof(ValidationSummary)} inside "  
                    $"an {nameof(EditForm)}.");
            }

            if (CurrentEditContext != _previousEditContext)
            {
                DetachValidationStateChangedListener();
                CurrentEditContext.OnValidationStateChanged  = _validationStateChangedHandler;
                _previousEditContext = CurrentEditContext;
            }
        }

        /// <inheritdoc />
        protected override void BuildRenderTree(RenderTreeBuilder builder)
        {
            // As an optimization, only evaluate the messages enumerable once, and
            // only produce the enclosing <ul> if there's at least one message
            var validationMessages = Model is null ?
                CurrentEditContext.GetValidationMessages() :
                CurrentEditContext.GetValidationMessages(new FieldIdentifier(Model, string.Empty));

            var first = true;
            foreach (var error in validationMessages)
            {
                if (first)
                {
                    first = false;

                    builder.OpenElement(0, "ul");
                    builder.AddMultipleAttributes(1, AdditionalAttributes);
                    builder.AddAttribute(2, "class", "validation-errors");
                }

                builder.OpenElement(3, "li");
                builder.AddAttribute(4, "class", "validation-message");
                builder.AddContent(5, error);
                builder.CloseElement();
            }

            if (!first)
            {
                // We have at least one validation message.
                builder.CloseElement();
            }
        }

        /// <inheritdoc/>
        protected virtual void Dispose(bool disposing)
        {
        }

        void IDisposable.Dispose()
        {
            DetachValidationStateChangedListener();
            Dispose(disposing: true);
        }

        private void DetachValidationStateChangedListener()
        {
            if (_previousEditContext != null)
            {
                _previousEditContext.OnValidationStateChanged -= _validationStateChangedHandler;
            }
        }
    }
}

If you need more help in building the component add some more detail of what you want to the question.

CodePudding user response：

This link might help you. It is totally posible. I had it done but I dont remember if this was this. https://docs.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.components.forms.editcontext.getvalidationmessages?view=aspnetcore-5.0#Microsoft_AspNetCore_Components_Forms_EditContext_GetValidationMessages

Try this first before I check my old codes thoroughly.