C#•7mo ago

Absolute Beginner - Accessing Variables From Other Classes

Hi. DecodeButton.cs:

using UnityEngine;

public class DecodeButton : MonoBehaviour
{
    void Start()
    {
        Decoders decoder = new Decoders();
    }

    void OnClick()
    {
        Decoders.CaesarCipher(ReadStringInput.input);
    }
}

using UnityEngine;

public class DecodeButton : MonoBehaviour
{
    void Start()
    {
        Decoders decoder = new Decoders();
    }

    void OnClick()
    {
        Decoders.CaesarCipher(ReadStringInput.input);
    }
}

ReadStringInput.cs:

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

public class ReadStringInput : MonoBehaviour
{
    public string input;
    
    // Start is called before the first frame update
    void Start()
    {
        
    }

    // Update is called once per frame
    void Update()
    {
        
    }

    public void ReadInput(string s)
    {
        input = s;
    }
}

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

public class ReadStringInput : MonoBehaviour
{
    public string input;
    
    // Start is called before the first frame update
    void Start()
    {
        
    }

    // Update is called once per frame
    void Update()
    {
        
    }

    public void ReadInput(string s)
    {
        input = s;
    }
}

In DecodeButton.cs, I'm getting the error CS0120 about Object references but frankly I'm not understanding it. Can someone help me out?

53 Replies

AdiZ•7mo ago

The exact error text is:

An object reference is required for the non-static field, method, or property 'ReadStringInput.input'

An object reference is required for the non-static field, method, or property 'ReadStringInput.input'

Thinker•7mo ago

The error is telling you that you need an instance to access the input field

AdiZ•7mo ago

Oh right The word reference was confusing me Thank you! I'll try it really quickly I changed DecodeButton.cs to this:

using UnityEngine;

public class DecodeButton : MonoBehaviour
{
    void Start()
    {
        Decoders decoder = new Decoders();
        ReadStringInput readStringInput = new ReadStringInput();
    }

    void OnClick()
    {
        string output = Decoders.CaesarCipher(readStringInput.input);
    }
}

using UnityEngine;

public class DecodeButton : MonoBehaviour
{
    void Start()
    {
        Decoders decoder = new Decoders();
        ReadStringInput readStringInput = new ReadStringInput();
    }

    void OnClick()
    {
        string output = Decoders.CaesarCipher(readStringInput.input);
    }
}

@🌈 Thinker 🌈 but i get a different error now Just that readStringInput doesn't exist I'm guessing that this is because the IDE doesn't know whether Start() will be called before OnClick()? But Unity still doesn't let me run the app

Thinker•7mo ago

You're creating a variable readStringInput which is local to Start, it's destroyed immediately after the method stops.

AdiZ•7mo ago

But I can't really define it outside of the method, right?

Thinker•7mo ago

yes you can You did that with input

AdiZ•7mo ago

Well isn't that a good point So just

ReadStringInput readStringInput;

ReadStringInput readStringInput;

? Or do I include the new() bit as well And then actually create the instance just before using it

Thinker•7mo ago

yep Also about this, this is something called scope which determines where and how variables are accessible. It's a pretty fundamental concept, so it's quite important to know about

AdiZ•7mo ago

Yeah I understand it from Python, just kinda forgot it here haha - still getting into the frame of mind needed for coding Would it also work if I instantiated it within the scope of the entire class?

Thinker•7mo ago

Yeah, and C# is quite different from Python

AdiZ•7mo ago

Oh yeah Definitely Quite cool though

Thinker•7mo ago

Well yes, but that works a bit differently

AdiZ•7mo ago

How so?

Thinker•7mo ago

Fields (variables in a class) cannot depend on each other, and you wouldn't be able to call any Unity methods from a field initializer.

AdiZ•7mo ago

So what could I use that for?

Thinker•7mo ago

class Foo : MonoBehavior
{
    private int x = GetComponent<Bar>().Value;
}

class Foo : MonoBehavior
{
    private int x = GetComponent<Bar>().Value;
}

This wouldn't work

AdiZ•7mo ago

Thinker•7mo ago

You set the value in Start or similar

AdiZ•7mo ago

And that is because it cannot change? So that value must always be the same so it can't depend on what GetComponent<Bar>().Value actually is?

Thinker•7mo ago

not exactly In field initializers, Unity methods do not work

AdiZ•7mo ago

Got it

Thinker•7mo ago

You have to set the value of fields in Start or some other method Though of course this is just in Unity

AdiZ•7mo ago

Yes I understand Not exactly why Unity methods don't work, though

Thinker•7mo ago

Do you know what a constructor is?

AdiZ•7mo ago

Somewhat, yes Called when the class is instantiated

Thinker•7mo ago

yep

AdiZ•7mo ago

Sets some intial fields' values depending on parameters That's about the extent of my knowledge on them

Thinker•7mo ago

So field initializers are actually just put inside the class's constructor. Unity doesn't let you use constructors for MonoBehavior classes, for various reasons including multithreading (I believe). Constructors are called before the object has any information about its place in the scene, eg. what components it has, its transform, etc., and this prevents you from calling Unity methods in said constructor.

AdiZ•7mo ago

That makes a lot of sense Pretty logical to be fair

Thinker•7mo ago

However Start is called after this initialization is complete, therefore you have to initialize fields from there.

AdiZ•7mo ago

Got it So Start() is effectively your constructor when using Unity

Thinker•7mo ago

yep

AdiZ•7mo ago

Okay Thank you, that's actually quite useful to know

Thinker•7mo ago

AdiZ•7mo ago

Really quick, I saw this thing in codecademy at school that's like if ? myBool x : y Something vaguely resembling that Like a really short if/else statement to set the value of a variable And I've completely forgotten it

Thinker•7mo ago

int x = c ? a : b;

// same as

int x;
if (c)
{
    x = a;
}
else
{
    x = b;
}

int x = c ? a : b;

// same as

int x;
if (c)
{
    x = a;
}
else
{
    x = b;
}

AdiZ•7mo ago

That's the one Brilliant Thank you

Thinker•7mo ago

yeah, it's quite useful

AdiZ•7mo ago

Now I've just got to figure out how to restrict the contents of an Input Field in Unity to digits Shouldn't be too hard But knowing me I'll make some super complicated method for doing it when there's already a built-in function or something 😢

Thinker•7mo ago

Hint: use int.TryParse

AdiZ•7mo ago

Yep I'm using that rn Just don't want to run that over every char every time the field is edited I feel like Unity will have something in there that does it for me @🌈 Thinker 🌈

AdiZ•7mo ago

AdiZ•7mo ago

I'm now just getting a bunch of these errors This is the script that is supposedly causing issues:

using UnityEngine;

public class DecodeButton : MonoBehaviour
{
    ReadStringInput plaintextStringInput;
    ReadStringInput shuffleStringInput;

    void Start()
    {
        plaintextStringInput = new ReadStringInput();
        shuffleStringInput = new ReadStringInput();
    }

    void OnClick()
    {
        int shuffle = 0;
        // string output = Decoders.CaesarCipher(plaintextStringInput.input);
    }
}

using UnityEngine;

public class DecodeButton : MonoBehaviour
{
    ReadStringInput plaintextStringInput;
    ReadStringInput shuffleStringInput;

    void Start()
    {
        plaintextStringInput = new ReadStringInput();
        shuffleStringInput = new ReadStringInput();
    }

    void OnClick()
    {
        int shuffle = 0;
        // string output = Decoders.CaesarCipher(plaintextStringInput.input);
    }
}

AdiZ•7mo ago

https://discussions.unity.com/t/you-are-trying-to-create-a-monobehaviour-using-the-new-keyword-this-is-not-allowed/97887

Unity Discussions

You are trying to create a MonoBehaviour using the 'new' keyword. ...

You are trying to create a MonoBehaviour using the ‘new’ keyword. This is not allowed. MonoBehaviours can only be added using AddComponent(). Alternatively, your script can inherit from ScriptableObject or no base class at all I am trying to connect these two scripts and I don’t know which one this error is for. The full error is: You...

AdiZ•7mo ago

Looking at this link, it suggests MyScript script = obj.AddComponent<MyScript>(); However I don't understand the syntax We're creating a script - where does it go? Is it a temporary file? Why are we adding a component? Also isn't MonoBehaviour.Awake() Unity's version of a constructor?

AdiZ•7mo ago

I was doing some reading and found this: https://docs.unity3d.com/ScriptReference/MonoBehaviour.Awake.html

AdiZ•7mo ago

Found the fix for this.

AdiZ•7mo ago

https://github.com/AdiZ-1579887/CipherDecoderApp/tree/main/Assets/Scripts

GitHub

CipherDecoderApp/Assets/Scripts at main · AdiZ-1579887/CipherDecode...

Adi, Karter, Kavya. Contribute to AdiZ-1579887/CipherDecoderApp development by creating an account on GitHub.

AdiZ•7mo ago

You can find it here if you're curious 🙂

Thinker•7mo ago

Read what it says

Dharmang•7mo ago

Altho a bit late, I suggest watching tarodev's videos. Excellent resource and he also has a discord. https://www.youtube.com/watch?v=tE1qH8OxO2Y

Tarodev

YouTube

Unity Architecture for Noobs - Game Structure

Unity Architecture is one of those things which can completely overwhelm new devs. This video will introduce you to a handful of architectural design patterns, which shy away from over-engineering, allowing you to learn the basics and get on with developing your game. Simple patterns are perfectly fine for most projects solo devs and small teams...

Dharmang•7mo ago

it covers basically everything for beginners. I am also learning from it

AdiZ•7mo ago

@Dharmang thank you, definitely needed something like this, I'll go check it out.

Gaming

Programming

Absolute Beginner - Accessing Variables From Other Classes