如何使用局部变量作为类型？编译器说“它是一个变量，但像类型一样使用”。 [英] How to use local variable as a type? Compiler says "it is a variable but is used like a type"

问题描述

在运行时，我不知道变量 v1 是什么类型。
出于这个原因，我写了许多 if 语句：

At run-time, I don't know what type of variable v1 is. For this reason, I wrote many if else statements:

if (v1 is ShellProperty<int?>)
{
    v2 = (v1 as ShellProperty<int?>).Value;
}
else if (v1 is ShellProperty<uint?>)
{
    v2 = (v1 as ShellProperty<uint?>).Value;
}
else if (v1 is ShellProperty<string>)
{
    v2 = (v1 as ShellProperty<string>).Value;
}
else if (v1 is ShellProperty<object>)
{
    v2 = (v1 as ShellProperty<object>).Value;
}    

唯一的区别是 ShellProperty< AnyType> 。

因此，我决定使用反射来获取该属性，而不是使用很多 if 语句来编写它。在运行时键入：

So instead of writing this with a lot of if else statements, I decided to use reflection to get the property type at run-time:

 Type t1 = v1.GetType().GetProperty("Value").PropertyType;
 dynamic v2 = (v1 as ShellProperty<t1>).Value;

此代码获取 PropertyType c $ c> v1 并将其分配给局部变量 t1 ，但是在那之后，我的编译器说：

This code gets the PropertyType of v1 and assigns it to the local variable t1, but after that, my compiler says that:

t1是变量，但像类型一样使用

t1 is a variable but is used like a type

不允许我在 ShellProperty<> 内写 t1 。

请告诉我如何解决此问题以及如何获得比我现有的紧凑的代码。我需要创建一个新班吗？

Please tell me how to solve this problem and how to get more compact code than what I have. Do I need to create a new class?

推荐答案

您非常接近，您只是错过了对 MakeGenericType 。

You were very close, you were just missing a call to MakeGenericType.

我相信您的代码应如下所示：

I believe your code would look like the following:

Type t1 = v1.GetType().GetProperty("Value").PropertyType;
var shellPropertyType = typeof(ShellProperty<>);
var specificShellPropertyType = shellPropertyType.MakeGenericType(t1);
dynamic v2 = specificShellPropertyType.GetProperty("Value").GetValue(v1, null);

编辑：
正如@PetSerAl指出的那样，我添加了一些不必要的间接层。抱歉，OP，您可能想要一个像这样的班轮：

As @PetSerAl pointed out I added some layers of indirection that were unnecessary. Sorry OP, you probably want a one liner like:

dynamic v2 = v1.GetType().GetProperty("Value").GetValue(v1, null);

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