程式 :

 public class ClassExample
    {
        public string myString;
    }
    public struct StructExample {
        public string myString;
    }

    public class FieldInfo_SetValue
    {
        public static void Main()
        {

            ClassExample c = new ClassExample();
            StructExample s = new StructExample();
            object o = s;
            ArrayList al = new ArrayList();
            al.Add(s);

            Type cType = c.GetType();
            FieldInfo cFieldInfo = cType.GetField("myString");
            cFieldInfo.SetValue(c, "value");
            Console.WriteLine("ClassExample:" + c.myString);
           
            Type sType = s.GetType();
            FieldInfo sFieldInfo = sType.GetField("myString");
            sFieldInfo.SetValue(s,"value");
            Console.WriteLine("StructExample:" + s.myString);

            sFieldInfo.SetValue(o, "value");
            Console.WriteLine("objectExample:" + ((StructExample)o).myString);
           
            sFieldInfo.SetValue(al[0], "value");
            Console.WriteLine("ArrayList:" + ((StructExample)al[0]).myString);
   
            Console.Read();
        }
    } 

結果

ClassExample:value
StructExample:
objectExample:value
ArrayList:value

結果表明在

sFieldInfo.SetValue(s,"value"); ////這兒有個裝箱過程setvalue(s,"value")時s被copy了一份

//這樣操作的結果是在SetValue另一個StructExample  克隆被設定了值,但傳入的值StructExample   s並不會被改變
Console.WriteLine("StructExample:" + s.myString);

s.myString此時還是預設值String.Empty,解決的方法是傳入一個引用型別還不是值型別,比如將struct轉為object然後傳入.或其它任何辦法都行