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：

代码

[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：

 

 

代码

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

    }

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

    }

 

 

 

 

调用：

代码

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());
        }
    }