编译器错误 C3450
“type”:不是特性;不能指定 [System::AttributeUsageAttribute] 或 [Windows::Foundation::Metadata::AttributeUsageAttribute]
用户定义的托管特性必须继承自 AttributeCollection。 Windows 运行时特性必须在 Windows::Foundation::Metadata
命名空间中定义。
有关更多信息,请参见 User-Defined Attributes。
示例
下面的示例将生成 C3450,并演示如何修复此错误。
// C3450.cpp
// compile with: /clr
// C3450 expected
using namespace System;
using namespace System::Security;
using namespace System::Security::Permissions;
public ref class MyClass {};
class MyClass2 {};
[attribute(AttributeTargets::All)]
ref struct AtClass {
AtClass(Type ^) {}
};
[attribute(AttributeTargets::All)]
ref struct AtClass2 {
AtClass2() {}
};
// Apply the AtClass and AtClass2 attributes to class B
[AtClass(MyClass::typeid), AtClass2]
[AttributeUsage(AttributeTargets::All)]
// Delete the following line to resolve.
ref class B {};
// Uncomment the following line to resolve.
// ref class B : Attribute {};