指定.NET属性目标所需的基类 [英] Specify required base class for .NET attribute targets
问题描述
我试图创建与下面的code,但意外离开的子类的自定义的.NET属性。这产生在评论中所示的易于固定的编译错误。
//导致编译器错误CS0641:属性AttributeUsage'是
//仅适用于从System.Attribute派生类
[AttributeUsage(AttributeTargets.Class)
内部类ToolDeclarationAttribute
{
内部ToolDeclarationAttribute()
{
}
}
我的问题是如何编译器知道 [AttributeUsage]
属性只能应用到子类 System.Attribute
?使用.NET反射我看不出有什么特别的 AttributeUsageAttribute特性
类声明本身。不幸的是,这可能仅仅是由编译器本身产生的一个特例。
[Serializable接口,标记有ComVisible特性(真),AttributeUsage(AttributeTargets.Class,继承=真)
公共密封类AttributeUsageAttribute特性:属性
{
...
我想可以指定我的自定义属性只能被放置在一个特定的类(或接口)的子类。这可能吗?
我想可以指定我的自定义属性只能被放置在一个特定的类(或接口)的子类。这可能吗?
其实,有一种方法可以做到这一点,使用受保护的子类(而不是接口)
- 看的Restricting属性用法。要重现code(但不讨论):
抽象类MyBase {
[AttributeUsage(AttributeTargets.Property)
保护密封类SpecialAttribute:属性{}
}
类ShouldBeValid:MyBase {
[专题] //工作正常
公众诠释富{获得;组; }
}
MyBase的类ShouldBeInvalid {//不是一个子类
[专题] //类型或命名空间找不到
[MyBase.Special] //人迹罕至,由于保护级别
公众诠释吧{获得;组; }
}
I tried to create a custom .NET attribute with the code below but accidentally left off the subclass. This generated an easily-fixed compiler error shown in the comment.
// results in compiler error CS0641: Attribute 'AttributeUsage' is
// only valid on classes derived from System.Attribute
[AttributeUsage(AttributeTargets.Class)]
internal class ToolDeclarationAttribute
{
internal ToolDeclarationAttribute()
{
}
}
My question is how does the compiler know the [AttributeUsage]
attribute can only be applied to a subclass of System.Attribute
? Using .NET Reflector I don't see anything special on the AttributeUsageAttribute
class declaration itself. Unfortunately this might just be a special case generated by the compiler itself.
[Serializable, ComVisible(true), AttributeUsage(AttributeTargets.Class, Inherited=true)]
public sealed class AttributeUsageAttribute : Attribute
{
...
I would like to be able to specify that my custom attribute can only be placed on subclasses of a particular class (or interface). Is this possible?
I would like to be able to specify that my custom attribute can only be placed on subclasses of a particular class (or interface). Is this possible?
Actually, there is a way to do this for subclasses (but not interfaces) using protected
- see Restricting Attribute Usage. To reproduce the code (but not the discussion):
abstract class MyBase {
[AttributeUsage(AttributeTargets.Property)]
protected sealed class SpecialAttribute : Attribute {}
}
class ShouldBeValid : MyBase {
[Special] // works fine
public int Foo { get; set; }
}
class ShouldBeInvalid { // not a subclass of MyBase
[Special] // type or namespace not found
[MyBase.Special] // inaccessible due to protection level
public int Bar{ get; set; }
}
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