requiredif实体框架空场

Question

我验证基于使用自定义的验证在MVC另一个字段的字段，我碰到这个实施传来：

public class RequiredIfAttribute : ValidationAttribute 
    { 
     private String PropertyName { get; set; } 
     private String ErrorMessage { get; set; } 
     private Object DesiredValue { get; set; } 

     public RequiredIfAttribute(String propertyName, Object desiredvalue, String errormessage) 
     { 
      this.PropertyName = propertyName; 
      this.DesiredValue = desiredvalue; 
      this.ErrorMessage = errormessage; 
     } 

     protected override ValidationResult IsValid(object value, ValidationContext context) 
     { 
      Object instance = context.ObjectInstance; 
      Type type = instance.GetType(); 
      Object proprtyvalue = type.GetProperty(PropertyName).GetValue(instance, null); 
      if (proprtyvalue.ToString() == DesiredValue.ToString()) 
      { 
       return new ValidationResult(ErrorMessage); 
      } 
      return ValidationResult.Success; 
     } 
    } 

而且我有一个简单的类定义如下：

public class Person 
{ 
    public int PersonID { get; set; } 
    public string name { set; get; } 
    [RequiredIf("name","","Address is required")] 
    public string addr { get; set; } 
} 

当我运行页面，我得到一个Object reference not set to an instance of an object.错误，但改变了线[RequiredIf("name","John","Address is required")]产量预期的结果。我的问题是，你如何使用它来检查该字段是否为空。

我也试图改变行[RequiredIf("name",null,"Address is required")]，但我得到了同样的错误。

Answer 1

这似乎工作：

protected override ValidationResult IsValid(object value, ValidationContext context) 
     { 
      if (value != null) { return ValidationResult.Success; } 

      Object instance = context.ObjectInstance; 
      Type type = instance.GetType(); 
      Object proprtyvalue = type.GetProperty(PropertyName).GetValue(instance, null); 
      if (proprtyvalue == null) { 
       return new ValidationResult(ErrorMessage); 
      } 
      return ValidationResult.Success; 
     } 

Answer 2

你没有张贴你正在测试的实际实例化的人，所以我只是猜测：确保属性名的proprtyvalue是不是要调用toString（）就可以了之前空。所以，你的Person.Name不能空！