[AttributeUsage(AttributeTargets.All)]public class TestAttribute : Attribute{}[TestAttribute]//结构public struct TestStruct { }[TestAttribute]//枚举public enum TestEnum { }[TestAttribute]//类上public class TestClass{[TestAttribute]public TestClass() { }[TestAttribute]//字段private string _testField;[TestAttribute]//属性public string TestProperty { get; set; }[TestAttribute]//方法上[return: TestAttribute]//定义返回值的写法public string TestMethod([TestAttribute] string testParam)//参数上
    {throw new NotImplementedException();}}

[AttributeUsage(AttributeTargets.Property)]
public class StringLengthAttribute : Attribute
{private int _maximumLength;public StringLengthAttribute(int maximumLength){_maximumLength = maximumLength;}public int MaximumLength{get { return _maximumLength; }}
}

public class People
{[StringLength(8)]public string Name { get; set; }[StringLength(15)]public string Description { get; set; }
}

public class ValidationModel
{public void Validate(object obj){var t = obj.GetType();//由于我们只在Property设置了Attibute,所以先获取Propertyvar properties = t.GetProperties();foreach (var property in properties){//这里只做一个stringlength的验证，这里如果要做很多验证，需要好好设计一下,千万不要用if elseif去链接//会非常难于维护，类似这样的开源项目很多，有兴趣可以去看源码。if (!property.IsDefined(typeof(StringLengthAttribute), false)) continue;var attributes = property.GetCustomAttributes();foreach (var attribute in attributes){//这里的MaximumLength 最好用常量去做var maxinumLength = (int)attribute.GetType().GetProperty("MaximumLength").GetValue(attribute);//获取属性的值var propertyValue = property.GetValue(obj) as string;if (propertyValue == null)throw new Exception("exception info");//这里可以自定义，也可以用具体系统异常类if (propertyValue.Length > maxinumLength)throw new Exception(string.Format("属性{0}的值{1}的长度超过了{2}", property.Name, propertyValue, maxinumLength));}}}
}

private static void Main(string[] args)
{var people = new People(){Name = "qweasdzxcasdqweasdzxc",Description = "description"};try{new ValidationModel().Validate(people);}catch (Exception ex){Console.WriteLine(ex.Message);}Console.ReadLine();
}