[AttributeUsage(AttributeTargets.All)]
  public class TestAttribute : Attribute
  {
  }
  [TestAttribute]//結(jié)構(gòu)
  public struct TestStruct { }
  
  [TestAttribute]//枚舉
  public enum TestEnum { }


  [TestAttribute]//類上
  public class TestClass
  {
    [TestAttribute]
    public TestClass() { }
    
    [TestAttribute]//字段
    private string _testField;

    [TestAttribute]//屬性
    public string TestProperty { get; set; }

    [TestAttribute]//方法上
    [return: TestAttribute]//定義返回值的寫法
    public string TestMethod([TestAttribute] string testParam)//參數(shù)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();

    //由于我們只在Property設(shè)置了Attibute,所以先獲取Property
    var properties = t.GetProperties();
    foreach (var property in properties)
    {

      //這里只做一個(gè)stringlength的驗(yàn)證，這里如果要做很多驗(yàn)證，需要好好設(shè)計(jì)一下,千萬不要用if elseif去鏈接
      //會(huì)非常難于維護(hù)，類似這樣的開源項(xiàng)目很多，有興趣可以去看源碼。
      if (!property.IsDefined(typeof(StringLengthAttribute), false)) continue;

      var attributes = property.GetCustomAttributes();
      foreach (var attribute in attributes)
      {
        //這里的MaximumLength 最好用常量去做
        var maxinumLength = (int)attribute.GetType().
          GetProperty("MaximumLength").
          GetValue(attribute);

        //獲取屬性的值
        var propertyValue = property.GetValue(obj) as string;
        if (propertyValue == null)
          throw new Exception("exception info");//這里可以自定義，也可以用具體系統(tǒng)異常類

        if (propertyValue.Length > maxinumLength)
          throw new Exception(string.Format("屬性{0}的值{1}的長(zhǎng)度超過了{(lán)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();
}