c# - 自定义验证属性

Question

目前我尝试通过同一类的另一个属性来验证一个属性。我收到一个错误，告诉我以下内容：

非静态字段、方法或属性需要对象引用

对于以下代码片段，这种错误对我来说绝对有意义。但无论如何，由于属性 B 的值（在我的示例级别中），我尝试验证属性 A（在我的示例 OrderNumber 中）。

是否有可能通过使用验证注释来做到这一点？

这是目前我的代码：

    public class A
    {
        /// <summary>
        /// Level 
        /// </summary>
        public string Level { get; set; }

        public B B {get;set;}
    }

    public class B
    {
        /// <summary>
        /// Order Number
        /// </summary>
        [Level(A.Level)]
        public int? OrderNumber { get; set; }
    }



    public class LevelAttribute : ValidationAttribute
    {

        private string Dlevel { get; set; }

        public LevelAttribute(string dlevel)
        {
            this.Dlevel = dlevel;
        }

        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            if (value!=null && (Dlevel.Equals("D1")||Dlevel.Equals("D2")))
            {
                return new ValidationResult("Invalid Error Message");
            }
            return ValidationResult.Success;
        }
    }

感谢帮助。

Answer 1

Directly referencing an instance member (method, property, field) is not possible in a custom attribute constructor. But there is an indirect way by defining the property name and resolve the corresponding property value via reflection:

public class A
{
    public A()
    {
        Level = "D3";
    }

    public string Level { get; set; }

    public B B { get; set; }
}

public class B
{
    [Level("MyNamespace.A.Level")]
    public int? OrderNumber { get; set; }
}

public class LevelAttribute : ValidationAttribute
{
    private string PropName { get; set; }

    public LevelAttribute(string prop)
    {
        this.PropName = prop;
    }

    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        System.Reflection.PropertyInfo property = null;
        object objectinstance = null;

        if (this.PropName.Contains("."))
        {
            string classname = PropName.Substring(0, PropName.LastIndexOf("."));
            string prop = PropName.Substring(PropName.LastIndexOf(".") + 1);
            Type type = Type.GetType(classname);

            objectinstance = System.Activator.CreateInstance(type);
            property = type.GetProperty(prop, System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.Static | System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.NonPublic);
        }
        else
        {
            objectinstance = validationContext.ObjectInstance;
            property = validationContext.ObjectInstance.GetType().GetProperty(this.PropName, System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.Static | System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.NonPublic);
        }

        object propertyvalue = property.GetValue(objectinstance, new object[0]);

        if (value != null && propertyvalue != null && (propertyvalue.Equals("D1") || propertyvalue.Equals("D2")))
        {
            return new ValidationResult("Invalid Error Message");
        }
        return ValidationResult.Success;
    }
}