NET MAUI CommunityToolkit.MVVM邮件验证属性调用时抛出异常

我自定义了一个邮件验证属性，验证逻辑运行正常，但程序退出时会抛出System.Reflection.TargetInvocationException: 'Exception has been thrown by the target of an invocation.' 错误。移除该属性后一切恢复正常，其他自定义验证属性也能正常工作。

自定义Email验证属性代码 #

[AttributeUsage(AttributeTargets.Field | AttributeTargets.Property, AllowMultiple = false)]
public class EmailAttribute : RegularExpressionAttribute
{
    public EmailAttribute() : base(@"[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}")
    {
        this.ErrorMessage = "Please provide a valid email address";
    }
}

模型代码 #

public partial class LoginModel : BaseViewModel
{
    private string email = string.Empty;
    private string password = string.Empty;


    [Required]
    [MinLength(5)]
    [Email]
    public string Email
    {
        get => this.email;
        set
        {
            SetProperty(ref this.email, value, true);
            OnPropertyChanged("ErrorDictionary[Email]");
        }
    }

    [Required]
    [DataType(DataType.Password)]
    [MinLength(8)]
    public string Password
    {
        get => this.password;
        set
        {
            SetProperty(ref this.password, value, true);
            OnPropertyChanged("ErrorDictionary[Password]");
        }
    }
}

解决方案 #

方案1：改用系统内置验证属性 #

直接替换自定义的[Email]属性为.NET内置的EmailAddressAttribute，无需自定义实现，避免反射兼容性问题：

[Required]
[MinLength(5)]
[EmailAddress(ErrorMessage = "Please provide a valid email address")]
public string Email { ... }

方案2：重写自定义验证属性的实现 #

避免继承RegularExpressionAttribute，直接继承ValidationAttribute并实现验证逻辑，减少基类带来的反射冲突：

[AttributeUsage(AttributeTargets.Field | AttributeTargets.Property, AllowMultiple = false)]
public class EmailAttribute : ValidationAttribute
{
    private static readonly Regex _emailRegex = 
        new Regex(@"[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}", RegexOptions.Compiled | RegexOptions.Singleline);

    public override bool IsValid(object value)
    {
        if (value is not string email) return false;
        return string.IsNullOrEmpty(email) || _emailRegex.IsMatch(email);
    }

    public override string FormatErrorMessage(string name)
    {
        return "Please provide a valid email address";
    }
}

方案3：调整ViewModel的属性变更通知逻辑 #

将OnPropertyChanged("ErrorDictionary[Email]")改为更标准的写法，避免字符串索引可能引发的反射问题：

OnPropertyChanged(nameof(ErrorDictionary));

或者确保ErrorDictionary的更新逻辑能够正确处理属性变更，避免在清理阶段触发异常。

内容的提问来源于stack exchange，提问作者Wasyster