How do I fix this bug in Unity C# with getting a variable through reflection?

Question

I have this code to find my variable:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.EventSystems;
using System.Reflection;
using System;

public class Shop : MonoBehaviour
{
    public MoneyScript MS;

    [SerializeField] GameObject ChosenObject;
    string VarName = "speed";
    public float Price;

    public void OnMouseDown()
    {
        var Instance = ChosenObject.GetComponent<UpgradeValues>();
        var Value = typeof(UpgradeValues).GetField(VarName, BindingFlags.Public | BindingFlags.Instance).GetValue(Instance);
        Value = 100;
    }
}

And the variable lies in this script. It is minimal because I just want to know how to use this for my actual project.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class UpgradeValues : MonoBehaviour
{
    public float speed = 3;
}

I was tried this code and it didn't supply any bugs! But, the variable was simply not converting.

Answer 1

Why does yours not work?

Your Value from

var Value = typeof(UpgradeValues).GetField(VarName, BindingFlags.Public | BindingFlags.Instance).GetValue(Instance);

is a simple float (boxed in object). This is a Value type - meaning it is no reference but always a copy of the value in memory - and is in no way at all linked to the underlying field where you originally copied this value from!

So when you do

Value = 100;

all you do is overwriting your local value of your Value variable. This would actually even be the case if your field was a reference type anyway since as said you are just re-assigning your variable, not modifying any property of the thing you stored in it.

---

(Preferred) Solution

Well you would actually first of all not use Reflection at all in your use case!

You already have the according instance reference

var Instance = ChosenObject.GetComponent<UpgradeValues>();

your field is public so visible to all anyway. So you would rather simply go through

Instance.speed = 100f;

Done!

You could even go further and directly use the correct type for your exposed field and do (you will have to re-assign the field(s))

[SerializeField] private UpgradeValues ChosenObject;

and then simply do

ChosenObject.speed = 100f;

---

Reflection (don't!)

IF for whatever weird reason you still want to use reflection

You would rather store the FieldInfo reference

var valueField = typeof(UpgradeValues).GetField(VarName, BindingFlags.Public | BindingFlags.Instance);

and then use

valueField.SetValue(Instance, 100f);

but again: I really don't see any reason why you would go for this in your case