无法在匿名方法中使用ref或out参数 [英] Cannot use ref or out parameter inside an anonymous method

问题描述

如果有人可以解决我的问题，我在c#中的代码有问题.

I have a problem with my code in c# if someone could help resolve my problem.

在一个函数中，我正在解析Xml文件并将其保存到结构中.

In a function I am parsing a Xml file and saving it to a struct.

然后我尝试从具有特定节点ID的结构中检索一些信息，并且我的代码失败

Then I try to retreive some info from said struct with a specific node id and my code fails with

不能在匿名方法，lambda表达式或查询表达式中使用ref或out参数'c'"

"Cannot use ref or out parameter 'c' inside an anonymous method, lambda expression, or query expression"

这是我的代码:

public void XmlParser(ref Point a, ref Point b, ref Point c)
{
     XDocument xdoc = XDocument.Load(XmlDirPath); 
     var coordinates = from r in xdoc.Descendants("move")
                        where int.Parse(r.Attribute("id").Value) == c.NodeID  // !! here is the error !!
                        select new
                        {
                              X = r.Element("x").Value,
                              Y = r.Element("y").Value,
                              Z = r.Element("z").Value, 
                              nID = r.Attribute("id").Value
                         };

     foreach (var r in coordinates)
     {
          c.x = float.Parse(r.X1, CultureInfo.InvariantCulture);
          c.y = float.Parse(r.Y1, CultureInfo.InvariantCulture);
          c.z = float.Parse(r.Z1, CultureInfo.InvariantCulture);
          c.NodeID = Convert.ToInt16(r.nID);
     }
}

public struct Point
{
    public  float x;
    public  float y;
    public  float z;
    public  int   NodeID;
}

推荐答案

好吧，您不能在匿名方法或lambda中使用ref或out参数，就像编译器错误指出的那样

Well, you're not allowed to use a ref or a out parameter in an anonymous method or a lambda, just as the compiler error says.

相反，您必须将ref参数中的值复制到局部变量中并使用该变量:

Instead you have to copy the value out of the ref parameter into a local variable and use that:

var nodeId = c.NodeID;
var coordinates = from r in xdoc.Descendants("move")
    where int.Parse(r.Attribute("id").Value) == nodeId
    ...

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