.NET泛型方法问题 [英] .NET Generic Method Question

问题描述

我试图掌握.NET泛型的概念和实际使用他们自己的code，但我依然会碰到的一个问题。

I'm trying to grasp the concept of .NET Generics and actually use them in my own code but I keep running into a problem.

可有人试图向我解释为什么以下安装不能编译？

Can someone try to explain to me why the following setup does not compile?

public class ClassA
{
	ClassB b = new ClassB();

	public void MethodA<T>(IRepo<T> repo) where T : ITypeEntity
	{
		b.MethodB(repo);
	}
}

public class ClassB
{
	IRepo<ITypeEntity> repo;

	public void MethodB(IRepo<ITypeEntity> repo)
	{
		this.repo = repo;
	}
}

我收到以下错误：
不能从IRepo＆LT转换，'T>为IRepo＆LT;'ITypeEntity>

I get the following error:
cannot convert from IRepo<'T> to IRepo<'ITypeEntity>

治法被调用了IRepo＆LT;DetailType>目标参数，其中DetailType从ITypeEntity继承

MethodA gets called with a IRepo<'DetailType> object parameter where DetailType inherits from ITypeEntity.

我一直在想，这应该编译为我牛逼约束内治法为类型ITypeEntity的。

I keep thinking that this should compile as I'm constraining T within MethodA to be of type ITypeEntity.

任何想法或意见，将非常有帮助。

Any thoughts or feedback would be extremely helpful.

感谢。

编辑：尼克R有一个伟大的建议，但遗憾的是在我的情况下，我没有做通用的ClassA的选择。 ClassB的可能，但。

Nick R has a great suggestion but unfortunately in my context, I don't have the option of making ClassA Generic. ClassB could be though.

推荐答案

继承使用泛型时不工作一样。由于Smashery指出，即使从类型A的TypeB，与的myType其中继承;类型A>不会从＆的myType其中继承;的TypeB>。

Inheritance doesn't work the same when using generics. As Smashery points out, even if TypeA inherits from TypeB, myType<TypeA> doesn't inherit from myType<TypeB>.

因此​​，你不能让一个呼叫定义为治法的方法;期待与的myType LT（ - 的myType LT>乙的TypeB）;类型B>，并给它一个 - 的myType其中，类型A>代替。问题的类型必须完全匹配。因此，以下不会编译：

As such, you can't make a call to a method defined as MethodA(myType<TypeB> b) expecting a myType<TypeB> and give it a myType<TypeA> instead. The types in question have to match exactly. Thus, the following won't compile:

myType<TypeA> a; // This should be a myType<TypeB>, even if it contains only TypeA's

public void MethodB(myType<TypeB> b){ /* do stuff */ }

public void Main()
{
  MethodB(a);
}

所以，你的情况，你需要传递一个IRepo＆LT; ITypeEntity>到方法b，即使它只包含DetailTypes。你需要做两者之间的一些转换。如果你使用的是通用的IList，你可以做到以下几点：

So in your case, you would need to pass in an IRepo<ITypeEntity> to MethodB, even if it only contains DetailTypes. You'd need to do some conversion between the two. If you were using a generic IList, you might do the following:

public void MethodA<T>(IList<T> list) where T : ITypeEntity
{
  IList<T> myIList = new List<T>();

  foreach(T item in list)
  {
    myIList.Add(item);
  }

  b.MethodB(myIList);
}

我希望这是有帮助的。

I hope this is helpful.

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