如何为Blazor ValidationMessage添加动态自定义文本？

方案一：自定义验证属性+手动替换消息 #

默认DataAnnotation属性无法直接绑定动态变量，你可以自定义支持占位符的验证属性，再在组件中替换占位符内容：

1. 自定义StringLength属性：

public class DynamicStringLengthAttribute : StringLengthAttribute
{
    public DynamicStringLengthAttribute(int maximumLength) : base(maximumLength)
    {
        ErrorMessage = "{FieldName}必须在3到100字符之间。";
        MinimumLength = 3;
    }
}

2. 在SearchFields类中使用自定义属性：

private class SearchFields
{
    [DynamicStringLength(100)]
    public string? FirstField { get; set; }
}

3. 组件中手动渲染验证消息并替换字段名：

<div class="row">
    <label class="col-12 col-sm-4 col-form-label">@FirstFieldLabel:</label>
    <div class="col-12 col-sm-8 ps-2">
        <InputText id="FirstField"
                   class="form-control form-control-sm"
                   @bind-Value="@SearchFields.FirstField" />
        @* 手动获取验证消息并替换占位符 *@
        @if (EditContext.GetValidationMessages(() => SearchFields.FirstField).Any())
        {
            foreach (var message in EditContext.GetValidationMessages(() => SearchFields.FirstField))
            {
                <div class="text-danger">@message.Replace("{FieldName}", FirstFieldLabel)</div>
            }
        }
    </div>
</div>

@code {
    private EditContext? EditContext { get; set; }
    private string? FirstFieldLabel { get; set; }
    private SearchFields SearchFields = new();

    protected override async Task OnInitializedAsync()
    {
        FirstFieldLabel = await _dbLayer.GetFirstFieldLabel();
        EditContext = new EditContext(SearchFields);
    }
}

方案二：使用FluentValidation（更灵活） #

FluentValidation支持动态构建错误消息，适合复杂场景：

1. 安装FluentValidation.Blazor包
2. 创建带动态字段名的验证器：

public class SearchFieldsValidator : AbstractValidator<SearchFields>
{
    private readonly string _fieldLabel;

    public SearchFieldsValidator(string fieldLabel)
    {
        _fieldLabel = fieldLabel;
        RuleFor(x => x.FirstField)
            .Length(3, 100)
            .WithMessage($"{_fieldLabel}必须在3到100字符之间。");
    }
}

3. 组件中注册验证器并使用：

@using FluentValidation.Blazor

<div class="row">
    <label class="col-12 col-sm-4 col-form-label">@FirstFieldLabel:</label>
    <div class="col-12 col-sm-8 ps-2">
        <InputText id="FirstField"
                   class="form-control form-control-sm"
                   @bind-Value="@SearchFields.FirstField" />
        <ValidationMessage For="() => SearchFields.FirstField" />
    </div>
</div>

@code {
    private EditContext? EditContext { get; set; }
    private string? FirstFieldLabel { get; set; }
    private SearchFields SearchFields = new();

    protected override async Task OnInitializedAsync()
    {
        FirstFieldLabel = await _dbLayer.GetFirstFieldLabel();
        EditContext = new EditContext(SearchFields);
        // 注册带动态字段名的验证器
        EditContext.AddFluentValidation(new SearchFieldsValidator(FirstFieldLabel));
    }
}

方案三：直接修改EditContext验证消息（简单粗暴） #

如果不想改动验证属性，可在获取动态字段名后手动替换验证消息：

<div class="row">
    <label class="col-12 col-sm-4 col-form-label">@FirstFieldLabel:</label>
    <div class="col-12 col-sm-8 ps-2">
        <InputText id="FirstField"
                   class="form-control form-control-sm"
                   @bind-Value="@SearchFields.FirstField" />
        <ValidationMessage For="() => SearchFields.FirstField" />
    </div>
</div>

@code {
    private EditContext? EditContext { get; set; }
    private string? FirstFieldLabel { get; set; }
    private SearchFields SearchFields = new();

    protected override async Task OnInitializedAsync()
    {
        FirstFieldLabel = await _dbLayer.GetFirstFieldLabel();
        EditContext = new EditContext(SearchFields);
        
        // 监听验证状态变化，替换消息
        EditContext.OnValidationStateChanged += (sender, args) =>
        {
            var fieldIdentifier = FieldIdentifier.Create(() => SearchFields.FirstField);
            var messages = EditContext.GetValidationMessages(fieldIdentifier).ToList();
            if (messages.Any())
            {
                EditContext.ClearValidationMessages(fieldIdentifier);
                EditContext.AddValidationMessage(fieldIdentifier, 
                    $"{FirstFieldLabel}必须在3到100字符之间。");
            }
        };
    }
}

内容的提问来源于stack exchange，提问作者PKD