C# 如何实例化一个给定字符串名称的类？
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How do I instantiate a class given its string name?
提问by ctrlShiftBryan
I have an abstract class and I want to initalize it to a class that extends it.
我有一个抽象类，我想将它初始化为一个扩展它的类。
I have the child classes name as a string.
我将子类名称作为字符串。
Besides this...
除此以外...
String childClassString;
MyAbstractClass myObject;
if (childClassString = "myExtenedObjectA")
myObject = new ExtenedObjectA();
if (childClassString = "myExtenedObjectB")
myObject = new ExtenedObjectB();
How can I do this? Basically how do I get rid of the if statements here?
我怎样才能做到这一点？基本上我如何摆脱这里的 if 语句？
采纳答案by Seth Petry-Johnson
Look at Activator.CreateInstance().
看看 Activator.CreateInstance()。
myObject = (MyAbstractClass)Activator.CreateInstance("AssemblyName", "TypeName");
or
或者
var type = Type.GetType("MyFullyQualifiedTypeName");
var myObject = (MyAbstractClass)Activator.CreateInstance(type);
回答by IAbstract
I believe this should work:
我相信这应该有效：
myObject = (MyAbstractClass)Activator.CreateInstance(null, childClassString);
The nullin the first parameter defaults to the current executing assembly. For more reference: MSDN
第null一个参数中的默认为当前正在执行的程序集。更多参考：MSDN
edit: forgot to cast to MyAbstractClass
编辑：忘了投 MyAbstractClass
回答by Kevin Fichter
I had some difficulty implementing some of the answers here because I was trying to instantiate an object from a different assembly (but in the same solution). So I thought I'd post what I found to work.
我在这里实现一些答案时遇到了一些困难，因为我试图从不同的程序集（但在相同的解决方案中）实例化一个对象。所以我想我会发布我发现的工作。
First, the Activator.CreateInstancemethod has several overloads. If you just call Activator.CreateInstance(Type.GetType("MyObj")), that assumes the object is defined in the current assembly, and it returns a MyObj.
首先，该Activator.CreateInstance方法有几个重载。如果您只是调用Activator.CreateInstance(Type.GetType("MyObj"))，则假定该对象已在当前程序集中定义，并返回一个MyObj.
If you call it as recommended in the answers here: Activator.CreateInstance(string AssemblyName, string FullyQualifiedObjectName), then it instead returns an ObjectHandle, and you need to call Unwrap()on it to get your object. This overload is useful when trying to call a method defined in a different assembly (BTW, you can use this overload in the current assembly, just leave the AssemblyNameparameter null).
如果您按照此处的答案中的建议调用它：Activator.CreateInstance(string AssemblyName, string FullyQualifiedObjectName)，那么它会返回一个ObjectHandle，您需要调用Unwrap()它来获取您的对象。当尝试调用在不同程序集中定义的方法时，此重载很有用（顺便说一句，您可以在当前程序集中使用此重载，只需将AssemblyName参数留空）。
Now, I found that the suggestion above to use typeof(ParentNamespace.ChildNamespace.MyObject).AssemblyQualifiedNamefor AssemblyNameactually gave me errors, and I could not get that to work. I'd get System.IO.FileLoadException(could not load file or assembly...).
现在，我发现上面使用typeof(ParentNamespace.ChildNamespace.MyObject).AssemblyQualifiedNamefor的建议AssemblyName实际上给了我错误，我无法让它起作用。我会得到System.IO.FileLoadException（无法加载文件或程序集...）。
What I did get to work is as follows:
我所做的工作如下：
var container = Activator.CreateInstance(@"AssemblyName",@"ParentNamespace.ChildNamespace.MyObject");
MyObject obj = (MyObject)container.Unwrap();
obj.DoStuff();
