问题描述
在下面的代码中，是否可以将x转换为要传递给 Activator.CreateInstance 的类型，而无需提前知道它是什么?我尝试传递 typeof ... ，但这不起作用.
In the code below, is it possible to convert x to the type you're passing into Activator.CreateInstance without knowing what it is ahead of time? I tried passing in typeof...but that doesn't work.
var testClasses = AppDomain.CurrentDomain.GetAssemblies()
.Single(a=>a.FullName.StartsWith("VerifyStuff")).GetTypes()
.Where(t=>t.UnderlyingSystemType.Name.StartsWith("VerifyXXX"));
var x = Activator.CreateInstance(testClasses.ElementAt(0));
谢谢！
推荐答案
您只需要强制转换:
MyObject x = (MyObject) Activator.CreateInstance(testClasses.ElementAt(0));
当然，如果您在 testClasses 中具有各种类型的类型，这将变得更加困难.如果它们都衍生自相同的基类或实现相同的接口，则可以强制转换为该基类或接口.
of course this is going to be more difficult if you have a whole range of types in testClasses. If they are all derived from the same base class or implement the same interface then you can cast to that base class or interface.
更多一点解释:x 是 是您传递给 CreateInstance 的类型，但它被强制转换为对象，因为CreateInstance不知道可能要扔给它什么.创建具体实例后会发生问题-无法将其传递给另一个(强类型化)函数，因为您将其作为 object .有两种解决方法:
just to be a little more explanatory: x is of the type you passed in to CreateInstance, but it is cast as an object, because CreateInstance has no idea what you may throw at it. You problem occurs after you've created your concrete instance - you can't pass it into another (strongly typed) function because you have it as an object. There are a couple of ways around this:
- 如上所述，
-
让它们全部派生自相同的基类或接口，以便您可以将它们作为该基类或接口类型进行传递
as i mentioned above, have them all derive from the same base class or interface, so that you can pass them around as that base class or interface type
如果您有一个需要在这些具体实例上执行操作的函数，请创建一个通用函数来执行此操作:
if you have a function that needs to perform an operation on those concrete instances, create a generic function to do it:
public T MyFunc(T myConcreteInstance)
{
... do whatever it is i need to do...
}
这很丑陋，但是可能很难避免...使用大的 if..else if 语句来确定它们的类型，然后再对其进行操作(提示:避免这种情况使用上面的选项#1 ...):
this is ugly, but it may be difficult to avoid... use a big if..else if statement to determine their types before operating on them (hint: to avoid this use option #1 above...):
Type t = myConcreteInstance.GetType();
if (t == typeof(someType1))
{
}
else if (t == typeof(someType2))
{
}
... etc ...
如果此时您在考虑为什么我不只是创建通用版本的CreateInstance()?" 然后不要打扰-已经有一个，但仍然没有解决在传递内容之前先进行强类型输入的问题.引用MSDN:
If at this point you are thinking "why don't i just make a generic version of CreateInstance()?" then don't bother - there already is one, it still doesn't solve your issue of having things strongly typed before passing them around. To quote MSDN:
如果要使用CreateInstance，这是因为您不提前知道类型，因此您必须解决该问题.
If you are going to use CreateInstance, it's because you don't know the type ahead of time, therefore you must work around it.
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