为什么不能使用Type.InvokeMember检索类型为out或ref的参数的值? [英] Why can't I retrieve the value for parameters of type out or ref using Type.InvokeMember?

问题描述

很长的标题，但我希望它具体.标题确实是个问题.即使 InvokeMember 所调用的方法具有一个 out 参数，并且正在将值分配给该参数，但我无法获取该值.这是我最初使用的代码:

A long title, but I wanted it to be specific. The title is really the question. Even though the method that InvokeMember is calling has an out parameter and is assigning a value to to that parameter I can't grab that value. Here is the code I was initially using:

string parameter = "";
int result = Convert.ToInt32(typeof(Ability).InvokeMember(selectedMove, BindingFlags.InvokeMethod | BindingFlags.Public | BindingFlags.Static, null, null, new object[] { parameter }));

我对此进行了更改，现在可以使其按预期运行，但我不知道为什么:

I changed it this, which now makes it work as intended but I don't know why:

object[] args = new object[1];      //necessary to retrieve ref/out parameter
int result = Convert.ToInt32(typeof(Ability).InvokeMember(selectedMove, BindingFlags.InvokeMethod | BindingFlags.Public | BindingFlags.Static, null, null, args));

推荐答案

在您的第一个代码示例中，对 InvokeMember 的调用不会修改 parameter 的值变量，它仅替换参数数组中的第一项(现在指向另一个 string 实例).由于未保留对此数组的引用，因此无法检索输出参数的值.

In your first code example, the call to InvokeMember doesn't modify the value of the parameter variable, it just replaces the first item in the parameter array (which now points to a different string instance). Since you didn't keep a reference to this array, you can't retrieve the value of the output parameter.

换句话说:该数组最初包含 parameter 变量的副本(即，对空字符串的引用的副本).调用后， parameter 和数组中的值引用2个不同的字符串实例.

In other words: the array initially contains a copy of the parameter variable (i.e. a copy of the reference to an empty string). After the call, parameter and the value in the array refer to 2 different string instances.

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