[英]Implementing Nullable Types in Generic Interface
So in a previous question I asked about implementing a generic interface with a public class and bingo, it works. 因此,在上一个问题中,我询问了如何使用公共类和宾果实现通用接口,它可以工作。 However, one of the types I'm looking to pass in is one of the built in nullable types such as: int, Guid, String, etc.
但是,我想要传入的其中一种类型是内置的可空类型之一,例如:int,Guid,String等。
Here's my Interface: 这是我的界面:
public interface IOurTemplate<T, U>
where T : class
where U : class
{
IEnumerable<T> List();
T Get(U id);
}
So when I implement this like so: 所以,当我这样实现时:
public class TestInterface : IOurTemplate<MyCustomClass, Int32>
{
public IEnumerable<MyCustomClass> List()
{
throw new NotImplementedException();
}
public MyCustomClass Get(Int32 testID)
{
throw new NotImplementedException();
}
}
I receive the error message: The type 'int' must be a reference type in order to use it as parameter 'U' in the generic type or method 'TestApp.IOurTemplate' 我收到错误消息: 类型'int'必须是引用类型才能在泛型类型或方法'TestApp.IOurTemplate'中将其用作参数'U'
I've tried to infer the type Int32?, but same error. 我试图推断类型Int32?,但同样的错误。 Any ideas?
有任何想法吗?
I wouldn't really do this but it's probably the only way to get it to work. 我不会真的这样做,但它可能是让它发挥作用的唯一方法。
public class MyWrapperClass<T> where T : struct
{
public Nullable<T> Item { get; set; }
}
public class MyClass<T> where T : class
{
}
Nullable types don't satisfy class
or struct
constraints: 可空类型不满足
class
或struct
约束:
C# Language Specification v3.0 (Section §10.1.5: Type parameter constraints):
C#语言规范v3.0(第10.1.5节:类型参数约束):
The reference type constraint specifies that a type argument used for the type parameter must be a reference type.
引用类型约束指定用于type参数的类型参数必须是引用类型。 All class types, interface types, delegate types, array types, and type parameters known to be a reference type (as defined below) satisfy this constraint.
已知为引用类型(如下定义)的所有类类型,接口类型,委托类型,数组类型和类型参数都满足此约束。 The value type constraint specifies that a type argument used for the type parameter must be a non-nullable value type.
值类型约束指定用于type参数的类型参数必须是非可空值类型。
All non-nullable struct types, enum types, and type parameters having the value type constraint satisfy this constraint.
具有值类型约束的所有非可空结构类型,枚举类型和类型参数都满足此约束。 Note that although classified as a value type, a nullable type (§4.1.10) does not satisfy the value type constraint.
请注意,虽然归类为值类型,但可空类型(第4.1.10节)不满足值类型约束。 A type parameter having the value type constraint cannot also have the constructor-constraint.
具有值类型约束的类型参数也不能具有构造函数约束。
Any reason why you need to restrict type U to class? 您需要将类型U限制为类的任何原因?
public interface IOurTemplate<T, U>
where T : class
{
IEnumerable<T> List();
T Get(U id);
}
public class TestInterface : IOurTemplate<MyCustomClass, Int32?>
{
public IEnumerable<MyCustomClass> List()
{
throw new NotImplementedException();
}
public MyCustomClass Get(Int32? testID)
{
throw new NotImplementedException();
}
}
FYI: int?
仅供参考:
int?
is the C# shorthand for Nullable<int>
. 是
Nullable<int>
的C#简写。
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