Instance variable modification during runtime using reflection

Question

I have been through the below code . Here i am not able to get/set the value of the variable during runtime . Variable value has been taken through console .

using System;
using System.Collections.Generic;
using System.Text;
using System.Reflection;

namespace ReflectionTest
{
    class Addition
    {
        public  int a = 5, b = 10, c = 20;
        public Addition(int a)
        {
            Console.WriteLine("Constructor called, a={0}", a);
        }
        public Addition()
        {
            Console.WriteLine("Hello");
        }
        protected Addition(string str)
        {
            Console.WriteLine("Hello");
        }

    }

    class Test
    {
        static void Main()
        {
            //changing  variable value during run time
            Addition add = new Addition();
            Console.WriteLine("a + b + c = " + (add.a + add.b + add.c));
            Console.WriteLine("Please enter the name of the variable that you wish to change:");
            string varName = Console.ReadLine();
            Type t = typeof(Addition);
            FieldInfo fieldInfo = t.GetField(varName ,BindingFlags.Public);
            if (fieldInfo != null)
            {
                Console.WriteLine("The current value of " + fieldInfo.Name + " is " + fieldInfo.GetValue(add) + ". You may enter a new value now:");
                string newValue = Console.ReadLine();
                int newInt;
                if (int.TryParse(newValue, out newInt))
                {
                    fieldInfo.SetValue(add, newInt);
                    Console.WriteLine("a + b + c = " + (add.a + add.b + add.c));
                }
                Console.ReadKey();
            }
       }
    }
  }

Thanks in advance ..

Answer 1

类中的字段是特定于实例的并且是公共的，但是您正在使用中午公共绑定标志而不是公共绑定标志，并且未应用实例绑定标志（对于位或使用|）。

Answer 2

There are multiple issues.

Firstly, you're passing BindingFlags.NonPublic . This won't work. You need to pass BindingFlags.Public and BindingsFlags.Instance like this:

t.GetField(varName, BindingFlags.Public | BindingFlags.Instance);

Or, just don't do it at all:

t.GetField(varName);

You can pass nothing at all because the implementation of GetField is this:

return this.GetField(name, BindingFlags.Instance | BindingFlags.Static | BindingFlags.Public);

So it does it for you.

Also, you need to pass instances of Addition to GetValue and SetValue , like so:

Console.WriteLine("The current value of " + 
    fieldInfo.Name + 
    " is " + 
    fieldInfo.GetValue(add) + ". You may enter a new value now:");
//                     ^^^ This

..and..

fieldInfo.SetValue(add, newInt);
//                 ^^^ This