我可以使用typeof（）来创建新对象吗？ [英] Can I use typeof() to make new objects?
问题描述
嗨。
我正在尝试以编程方式决定新对象应该具有哪种类型，
但是typeof-function显然不是答案，如下面的代码
将无法编译。
class AbstractClass：Object {}
class DerivedClass1：AbstractClass {}
类DerivedClass2：AbstractClass {}
静态类程序
{
static void Main（）
{
AbstractClass a，b，c;
a = new DerivedClass1（）;
b = new DerivedClass2（）;
if（some_condition）
c = new（typeof（a））（）;
else
c = new（typeof（b））（）;
}
}
如何实现这个？
最好的问候
Einar V？rnes
Einar V？rnes schrieb：
嗨。
我想亲从逻辑上决定新对象应该具有哪种类型，
但是typeof-function显然不是答案，因为以下代码
将无法编译。
类AbstractClass：Object {}
class DerivedClass1：AbstractClass {}
class DerivedClass2：AbstractClass {}
静态课程
{
static void Main（）
{
AbstractClass a，b，c;
a = new DerivedClass1（）;
b = new DerivedClass2（）;
if（some_condition）
c = new（typeof（a））（）;
else
c = new（typeof（b））（）;
}
}
如何实现这个？
查看System.Reflection命名空间。使用typeof，你将获得一个Type对象
。 Assembly类型有一个CreateInstance方法，
将创建一个类型的新对象：
AbstractClass myObject;
/ / ...
类型t = typeof（myObject）;
程序集a = Assembly.GetAssembly（t）;
AbstractClass newObject = a .CreateInstance（t.FullName）;
// ...
Assembly :: CreateInstance有几个签名。所以你可以将
传递给构造函数的参数，例如。
顺便说一下，如果没有提出你的问题，我觉得上课时很困惑
被命名为AbstractClass的但并未宣布为抽象。但那只是味道的美元。 :)
HTH，
Tobi
嗯，你已经创建了实例？在一个简单的层面上，
以下就足够了：
AbstractClass c;
if（some_condition）{
c = new DerivedClass1（）;
} else {
c = new DerivedClass2（）;
}
还有其他方法：
* Activator.CreateInstance（{各种重载}）
*来自你可以获得的反射并调用构造函数
*您可以将泛型与：new（）一起使用（也许是：
AbstractClass）条款
*您可以在现有实例上使用工厂界面
你能解释一下这个场景，找出一个可能的候选人吗？
注意typeof（）适用于类型定义，而不是实例;在您的
代码中，您将使用a.GetType（）和b.GetType（）来获取Type，
，可用于创建*附加*实例。
Tobias Schr？er schrieb：
AbstractClass myObject;
//。 ..
类型t = typeof（myObject）;
程序集a = Assembly.GetAssembly（t）;
AbstractClass newObject = a.CreateInstance （t.FullName）;
// ...
Argh，刚看到一个错误：
类型t = myObject.GetType（）; //不：输入t = typeof（myObject）;
这是对的，对不起。
Tobi
Hi.
I am trying to programatically decide which type a new object should have,
but the typeof-function is apparently not the answer, as the following code
will not compile.
class AbstractClass:Object { }
class DerivedClass1 : AbstractClass { }
class DerivedClass2 : AbstractClass { }
static class Program
{
static void Main()
{
AbstractClass a,b,c;
a = new DerivedClass1();
b = new DerivedClass2();
if (some_condition)
c = new (typeof(a))();
else
c = new (typeof(b))();
}
}
How can implement this?
Best regards
Einar V?rnes
Hi,
Einar V?rnes schrieb:Hi.
I am trying to programatically decide which type a new object should have,
but the typeof-function is apparently not the answer, as the following code
will not compile.
class AbstractClass:Object { }
class DerivedClass1 : AbstractClass { }
class DerivedClass2 : AbstractClass { }
static class Program
{
static void Main()
{
AbstractClass a,b,c;
a = new DerivedClass1();
b = new DerivedClass2();
if (some_condition)
c = new (typeof(a))();
else
c = new (typeof(b))();
}
}
How can implement this?Take a look into the System.Reflection namespace. With typeof you will
get a Type object. The Assembly type has a CreateInstance method, which
will create a new object of a type:
AbstractClass myObject;
// ...
Type t = typeof(myObject);
Assembly a = Assembly.GetAssembly(t);
AbstractClass newObject = a.CreateInstance(t.FullName);
// ...
There are several signatures for Assembly::CreateInstance. So you can
pass arguments to the constructor, for example.
Btw and not concering your question, I find it confusing to have a class
that is named "AbstractClass" but is not declared abstract. But that
just a metter of "taste" :)
HTH,
Tobi
Well, you already created the instances? At a simple level, the
following should suffice:
AbstractClass c;
if(some_condition) {
c = new DerivedClass1();
} else {
c = new DerivedClass2();
}
There are other approaches:
* Activator.CreateInstance({various overloads})
* from reflection you can obtain and invoke the constructor
* you can use generics with the ": new() " (and perhaps " :
AbstractClass") clause(s)
* you can perhaps use a factory interface on existing instances
Can you explain a little more about the scenario, to identify a likely
candidate?
Note that typeof() works on type-definitions, not instances; in your
code you would use a.GetType() and b.GetType() to obtain the Type,
which can be used to create *additional* instances.
Tobias Schr?er schrieb:
AbstractClass myObject;
// ...
Type t = typeof(myObject);
Assembly a = Assembly.GetAssembly(t);
AbstractClass newObject = a.CreateInstance(t.FullName);
// ...Argh, just saw an error:
Type t = myObject.GetType(); // not: Type t = typeof(myObject);
That would be correct, sorry.
Tobi
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