Unity Movement Questions

Question

I have recently been trying to learn how to make Unity games through Lynda.com using the tutorials provided by Jesse Freeman. But I have one issue, he doesn't explain any of the coding. This bit has me confused.

Body2D.AddForce (new Vector2 (forceX, forceY));

1.) Why is Body2D (this is a variable) separated by AddForce with a .?

2.) Why does a new vector2 have to be created?

3.) My last question isn't quite in the code itself but why must we add a () to methods?

(Full Code)

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

public class Player : MonoBehaviour {

public float Speed = 2.5f;
public Vector2 MaxVelocity = new Vector2 (5, 10);

private Rigidbody2D Body2D;
private SpriteRenderer Renderer2D;

// Use this for initialization
void Start () {
    Body2D = GetComponent<Rigidbody2D> ();
    Renderer2D = GetComponent<SpriteRenderer> ();

}

// Update is called once per frame
void Update () {
    var absValX = Mathf.Abs (Body2D.velocity.x);

    var forceX = 0f;
    var forceY = 0f;

    if (Input.GetKey("right")){
        if (absValX < MaxVelocity.x) {
            forceX = Speed;
        }
    } else if (Input.GetKey("left")) {
        if (absValX < MaxVelocity.x){
            forceX = -Speed;
        }
    }
    Body2D.AddForce (new Vector2 (forceX, forceY));

}

You should watch/do some tutorials/courses on programming and OOP in general. It will be easier to pick up the lessons this way. From my own experience it's hard to fully understand the programming unless you try to create something yourself. So rather than watching big chunks of data on some topic, try to learn small things. Search for them on the internet. But in the end you will need to read some books, articles. If you want to do game dev in parallel, then just copy line by line the code from tutorials, after that try to fully understand why it's working like that, search for info on it. — Candid Moon _Max_
– Candid Moon _Max_, Commented May 8, 2018 at 20:08

user1430 · Accepted Answer · 2018-05-08 17:53:03Z

But I have one issue, he doesn't explain any of the coding. This bit has me confused.

It sounds like the tutorials you are following assume a certain level of familiarity with the C# programming language used by Unity that you may not have. You may want to take a break from those tutorials to read a little bit about the language itself outside the context of Unity. The MSDN has some reference you might find helpful. At the very least you should consider looking at this material concurrently with the Unity tutorials.

1.) Why is Body2D (this is a variable) separated by AddForce with a .?

The "dot operator" is used to access members of a type (or namespace, but that isn't the case here). The type of variable Body2D has a collection of functions and properties, and the dot operator is used to access them -- in this case, to access and call the AddForce member function of whatever Body2D's type is.

2.) Why does a new vector2 have to be created?

The new operator is how all new instances of objects are created. AddForce() requires a Vector2 for its first parameter. One could create that vector earlier, like:

Vector2 force = new Vector(10, -1);
Body2D.AddForce(force);

or one could just create the new vector inside the function call, as in your original example.

3.) My last question isn't quite in the code itself but why must we add a () to methods?

The () in this case represent the invocation operator. They exist to indicate that the expression is a call to (an invocation of) some function, with parameters specified in between the opening ( and closing ). When you define methods, they're used to indicate what the parameters to that method (if any) are.

Thank you! You helped me with this so much! This will help me with my assignment. Thanks again! — user116244
– user116244, Commented May 9, 2018 at 17:26

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