[英]Check if generic parameter of a class implements an interface
I have a following generic class: 我有一个以下泛型类:
public class SearchResult<T>
{
public int ResultCount { get; set; }
public IEnumerable<T> Result { get; set; }
}
I also have a Bird
class, which implements IFlyble
interface: 我还有一个
Bird
类,它实现了IFlyble
接口:
public class Bird : IFlyable
{
public void Fly() {}
}
public interface IFlyable
{
void Fly();
}
I also have a variable res
of type object
. 我还有一个类型为
object
的变量res
。 How do I check if res
is a SearchResult<IFlyable>
? 如何检查
res
是否是SearchResult<IFlyable>
?
I tryied this way: 我这样试试:
if (res.GetType().IsAssignableFrom(typeof(SearchResult<IFlyable>)))
{
///
}
And this way: 这样:
if(res is SearchResult<IFlyable>)
{
///
}
But it does not seems to work. 但它似乎不起作用。
The problem you are having is probably due to the fact that SearchResult<Bird>
is not convertible to SearchResult<IFlyable>
because SearchResult<T>
is invariant in T
. 您遇到的问题可能是由于
SearchResult<Bird>
无法转换为SearchResult<IFlyable>
因为SearchResult<T>
在T
是不变的。
C# only admitís generic type variance in interfaces and delegates. C#只允许接口和委托中的泛型类型差异。 You need to define an
ISearchResult<>
interface that is covariant in its generic type. 您需要定义一个
ISearchResult<>
接口,该接口在其泛型类型中是协变的。
In your case, if it's accepatable that T
Is only used as an output you could define such interface as follows: 在您的情况下,如果可以接受
T
仅用作输出,则可以按如下方式定义此类接口:
public interface ISearchResult<out T>
{
int ResultCount { get; }
IEnumerable<T> Result { get; }
}
And now a ISearchResult<Bird>
is a ISearchResult<IFlyable>
because you've given the compiler enough information so that it can verify that the conversion is in fact safe 现在,
ISearchResult<Bird>
是一个ISearchResult<IFlyable>
因为您已经为编译器提供了足够的信息,以便它可以验证转换实际上是否安全
You can also try this using reflection, which also works and no need to create another interface. 您也可以使用反射来尝试这个,它也可以工作,不需要创建另一个接口。
static void Main()
{
var sr = new SearchResult<Bird>();
Console.WriteLine(IsSearchResultIFlyable(sr.GetType())
? "sr is SearchResult<IFlyable>"
: "sr is Not SearchResult<IFlyable>");
Console.ReadLine();
}
public static bool IsSearchResultIFlyable(Type t)
{
if (!t.IsGenericType) return false;
if (t.GetGenericTypeDefinition() != typeof(SearchResult<>)) return false;
var gr = t.GetGenericArguments();
return gr.Length == 1 && typeof(IFlyable).IsAssignableFrom(gr[0]);
}
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