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所调用的方法有一个out参数，并且正在为该参数分配一个值，我也无法获取该值.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变量的值，它只是替换了参数数组(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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