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 v1 是什么类型的变量.为此，我写了很多if else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;
}    

唯一的区别在于ShellProperty.

因此，我决定使用反射来在运行时获取属性类型，而不是使用大量 if else 语句编写此代码:

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;

这段代码获取了v1的PropertyType，并将其分配给了局部变量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 是一个变量，但像类型一样使用

t1 is a variable but is used like a type

所以它不允许我在 ShellProperty<> 中写入 t1.

So it does not allow me to write t1 inside ShellProperty<>.

请告诉我如何解决这个问题以及如何获得比我现有的更紧凑的代码.我需要创建一个新类吗?

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

你很接近，只是错过了对 MakeGenericType 的调用.

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

我相信您的代码如下所示:

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);

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衬里:

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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