自定义属性Attribute(二)

自定义属性类实例的比较，默认的Attribute.Match 只是简单的调用了Equal方法，我们可以重写此Match方法来精确定义对Attribute的比较。

代码：

自定义属性类：

[AttributeUsage(AttributeTargets.Class)]
    internal class AccountsAttribute : System.Attribute
    {
        private EnumAccounts m_accounts;

        public AccountsAttribute(EnumAccounts accounts)
        {
            this.m_accounts = accounts;
        }

        public override bool Match(object obj)
        {
            //if the base type is not System.Attribute
            //it is a Customer Attribute inhreit from System.Attribute
            //the next line should not be annotate
            //return base.Match(obj); 

            if (obj == null) 
                return false;

            if (this.GetType() != obj.GetType()) 
                return false;

            AccountsAttribute other = (AccountsAttribute)obj;
            if ((other.m_accounts & this.m_accounts) != this.m_accounts)
                return false;

            return true;
        }

        public override bool Equals(object obj)
        {
            //return base.Equals(obj);

            if (obj == null)
                return false;

            if (this.GetType() != obj.GetType())
                return false;

            AccountsAttribute other = (AccountsAttribute)obj;
            if (other.m_accounts != this.m_accounts)
                return false;

            return true;
        }

        public override int GetHashCode()
        {
            //return base.GetHashCode();

            return (Int32)m_accounts;
        }
    }

目标类：

 

 

　　[Accounts(EnumAccounts.Savings)]
    internal sealed class ChildAccount
    { 
    
    }

    [Accounts(EnumAccounts.Savings | EnumAccounts.Brokerage | EnumAccounts.Checking)]
    internal sealed class AdultAccount
    { 
    
    }

 

 

 

 

调用：

public class AccountsAdapter
    {
        private static void CanWriteCheck(object obj)
        {
            Attribute checking = new AccountsAttribute(EnumAccounts.Checking);

            Attribute validAccounts = Attribute.GetCustomAttribute(obj.GetType(), typeof(AccountsAttribute), false);

            if ((validAccounts != null) && checking.Match(validAccounts))
            {
                Console.WriteLine("{0} types can write checks.", obj.GetType());
            }
            else
            {
                Console.WriteLine("{0} types can not write checks.", obj.GetType());
            }
        }

        public static void AttributeMatch()
        {
            CanWriteCheck(new ChildAccount());
            CanWriteCheck(new AdultAccount());
            CanWriteCheck(new AccountsAdapter());
        }
    }