c# - MVVM - 验证真的需要这么麻烦吗？

Question

在我的应用程序中，我有大量的表单，其中大部分都有自己的绑定(bind)模型!当然数据验证很重要，但是没有比为所有模型实现 IDataErrorInfo 然后为所有属性编写代码来验证它们更好的解决方案了吗？

我已经创建了验证助手，它删除了很多实际的验证代码，但我仍然忍不住觉得我错过了一两个技巧!我可以补充一点，这是我在其中使用 MVVM 的第一个应用程序，所以我确信我在这个主题上还有很多东西要学习!

编辑:

这是我非常不喜欢的典型模型的代码(让我解释一下):

    string IDataErrorInfo.Error
    {
        get
        {
            return null;
        }
    }

    string IDataErrorInfo.this[string propertyName]
    {
        get
        {
            return GetValidationError(propertyName);
        }
    }

    #endregion

    #region Validation

    string GetValidationError(String propertyName)
    {
        string error = null;

        switch (propertyName)
        {
            case "carer_title":
                error = ValidateCarerTitle();
                break;
            case "carer_forenames":
                error = ValidateCarerForenames();
                break;
            case "carer_surname":
                error = ValidateCarerSurname();
                break;
            case "carer_mobile_phone":
                error = ValidateCarerMobile();
                break;
            case "carer_email":
                error = ValidateCarerEmail();
                break;
            case "partner_title":
                error = ValidatePartnerTitle();
                break;
            case "partner_forenames":
                error = ValidatePartnerForenames();
                break;
            case "partner_surname":
                error = ValidatePartnerSurname();
                break;
            case "partner_mobile_phone":
                error = ValidatePartnerMobile();
                break;
            case "partner_email":
                error = ValidatePartnerEmail();
                break;
        }

        return error;
    }

    private string ValidateCarerTitle()
    {
        if (String.IsNullOrEmpty(carer_title))
        {
            return "Please enter the carer's title";
        }
        else
        {
            if (!ValidationHelpers.isLettersOnly(carer_title))
                return "Only letters are valid";
        }

        return null;
    }

    private string ValidateCarerForenames()
    {
        if (String.IsNullOrEmpty(carer_forenames))
        {
            return "Please enter the carer's forename(s)";
        }
        else
        {
            if (!ValidationHelpers.isLettersSpacesHyphensOnly(carer_forenames))
                return "Only letters, spaces and dashes are valid";
        }

        return null;
    }

    private string ValidateCarerSurname()
    {
        if (String.IsNullOrEmpty(carer_surname))
        {
            return "Please enter the carer's surname";
        }
        else
        {
            if (!ValidationHelpers.isLettersSpacesHyphensOnly(carer_surname))
                return "Only letters, spaces and dashes are valid";
        }

        return null;
    }

    private string ValidateCarerMobile()
    {
        if (String.IsNullOrEmpty(carer_mobile_phone))
        {
            return "Please enter a valid mobile number";
        }
        else
        {
            if (!ValidationHelpers.isNumericWithSpaces(carer_mobile_phone))
                return "Only numbers and spaces are valid";
        }

        return null;
    }

    private string ValidateCarerEmail()
    {
        if (String.IsNullOrWhiteSpace(carer_email))
        {
            return "Please enter a valid email address";
        }
        else
        {
            if (!ValidationHelpers.isEmailAddress(carer_email))
                return "The email address entered is not valid";
        }
        return null;
    }

    private string ValidatePartnerTitle()
    {
        if (String.IsNullOrEmpty(partner_title))
        {
            return "Please enter the partner's title";
        }
        else
        {
            if (!ValidationHelpers.isLettersOnly(partner_title))
                return "Only letters are valid";
        }

        return null;
    }

    private string ValidatePartnerForenames()
    {
        if (String.IsNullOrEmpty(partner_forenames))
        {
            return "Please enter the partner's forename(s)";
        }
        else
        {
            if (!ValidationHelpers.isLettersSpacesHyphensOnly(partner_forenames))
                return "Only letters, spaces and dashes are valid";
        }

        return null;
    }

    private string ValidatePartnerSurname()
    {
        if (String.IsNullOrEmpty(partner_surname))
        {
            return "Please enter the partner's surname";
        }
        else
        {
            if (!ValidationHelpers.isLettersSpacesHyphensOnly(partner_surname))
                return "Only letters, spaces and dashes are valid";
        }

        return null;
    }

    private string ValidatePartnerMobile()
    {
        if (String.IsNullOrEmpty(partner_mobile_phone))
        {
            return "Please enter a valid mobile number";
        }
        else
        {
            if (!ValidationHelpers.isNumericWithSpaces(partner_mobile_phone))
                return "Only numbers and spaces are valid";
        }

        return null;
    }

    private string ValidatePartnerEmail()
    {
        if (String.IsNullOrWhiteSpace(partner_email))
        {
            return "Please enter a valid email address";
        }
        else
        {
            if (!ValidationHelpers.isEmailAddress(partner_email))
                return "The email address entered is not valid";
        }
        return null;
    }

    #endregion

用一个 switch 语句来识别正确的属性，然后必须为每个属性编写唯一的验证函数的想法感觉太多了(不是在工作量方面，而是在所需的代码量方面)。也许这是一个优雅的解决方案，但它就是不像一个解决方案!

注意:我将按照其中一个答案中的建议将我的验证助手转换为扩展(感谢 Sheridan)

解决方案:

所以，按照我接受的答案，这是我为让它最初工作而实现的基本框架(显然我会改进部分 - 但我只是想先让它开始，因为我没有使用 lambda 的经验实现之前的表达或反射(reflection))。

Validtion Dictionary 类(显示主要功能):

    private Dictionary<string, _propertyValidators> _validators;
    private delegate string _propertyValidators(Type valueType, object propertyValue);


    public ValidationDictionary()
    {
        _validators = new Dictionary<string, _propertyValidators>();
    }

    public void Add<T>(Expression<Func<string>> property, params Func<T, string>[] args)
    {
        // Acquire the name of the property (which will be used as the key)
        string propertyName = ((MemberExpression)(property.Body)).Member.Name;

        _propertyValidators propertyValidators = (valueType, propertyValue) =>
        {
            string error = null;
            T value = (T)propertyValue;

            for (int i = 0; i < args.Count() && error == null; i++)
            {
                error = args[i].Invoke(value);
            }

            return error;
        };

        _validators.Add(propertyName, propertyValidators);
    }

    public Delegate GetValidator(string Key)
    {
        _propertyValidators propertyValidator = null;
        _validators.TryGetValue(Key, out propertyValidator);
        return propertyValidator;
    }

模型实现:

public FosterCarerModel()
    {
        _validationDictionary = new ValidationDictionary();
        _validationDictionary.Add<string>( () => carer_title, IsRequired);
    }

    public string IsRequired(string value)
    { 
        string error = null;

        if(!String.IsNullOrEmpty(value))
        {
            error = "Validation Dictionary Is Working";
        }

        return error;
    }

IDataErrorInfo 实现(模型实现的一部分):

string IDataErrorInfo.this[string propertyName]
    {
        get
        {
            Delegate temp = _validationDictionary.GetValidator(propertyName);

            if (temp != null)
            {
                string propertyValue = (string)this.GetType().GetProperty(propertyName).GetValue(this, null);
                return (string)temp.DynamicInvoke(typeof(string), propertyValue);
            }                

            return null;
        }
    }

忽略我草率的命名约定和地方编码，我很高兴能让它工作!当然要特别感谢 nmclean，还要感谢为这个问题做出贡献的每个人，所有回复都非常有帮助，但经过一番考虑后我决定采用这种方法!

Answer 1

我使用 extension 方法来减少我必须编写的验证文本的数量。如果您不熟悉它们，请查看 Extension Methods (C# Programming Guide) MSDN 上的页面以了解有关 extension 方法的信息。我有几十个这样的验证每一种情况。例如:

if (propertyName == "Title" && !Title.ValidateMaximumLength(255)) error = 
    propertyName.GetMaximumLengthError(255);

在 Validation.cs 类中:

public static bool ValidateMaximumLength(this string input, int characterCount)
{
    return input.IsNullOrEmpty() ? true : input.Length <= characterCount;
}

public static string GetMaximumLengthError(this string input, int characterCount, 
    bool isInputAdjusted)
{
    if (isInputAdjusted) return input.GetMaximumLengthError(characterCount);
    string error = "The {0} field requires a value with a maximum of {1} in it.";
    return string.Format(error, input, characterCount.Pluralize("character"));
}

请注意，Pluralize 是另一种扩展 方法，如果输入值不等于 1，它会在输入参数的末尾简单地添加一个“s”。另一种方法可能是:

public static bool ValidateValueBetween(this int input, int minimumValue, int 
    maximumValue)
{
    return input >= minimumValue && input <= maximumValue;
}

public static string GetValueBetweenError(this string input, int minimumValue, int 
    maximumValue)
{
    string error = "The {0} field value must be between {1} and {2}.";
    return string.Format(error, input.ToSpacedString().ToLower(), minimumValue, 
        maximumValue);
}

当然，实现您需要的所有方法需要一些时间，但之后您将节省大量时间，并且您将获得所有错误消息保持一致的额外好处。