Look, I know programming. Getting into Unity now. Started following a tutorial on scripting but got stuck mentally on the first step.
He's trying to explain how GetComponent works but does a really poor job.
So, this is the code:

public Rigidbody rigid;

void Start () {

rigid = GetComponent<Rigidbody>();

}

Now what I don't understand is if rigid is already declared as the type Rigidbody why does it have to be assigned via GetComponent?
If someone could explain this I would be sooo happy.
Thanks,

Compu

Quote

Now what I don't understand is if rigid is already declared as the type Rigidbody why does it have to be assigned via GetComponent?

So, if you declare a variable of type Rigidbody, which is class

public Rigidbody rigid;

You have a null object, since class needs to be initialized. To make an instance of a class you'd normally use a new keyword or if the instance already exists, you want to get it, this.GetComponent<T>() lets you get an existing instance of type T from GameObject that has this script attached to. There is also another way to get the instance - since this field is public, it's also serialized, so you'll see an empty field in inspector where you can drag there which rigidody you want to access.

Unity won't automatically inject instance to this field since it would be less flexible and would make too much magic.

By the way, if it doesn't need to be public, don't make it public. If you want to see fields in inspector, you can use [SerializeField] attribute. Remember about encapsulation.

On 3/8/2019 at 9:20 AM, Prastiwar said:

So, if you declare a variable of type Rigidbody, which is class

public Rigidbody rigid;

You have a null object, since class needs to be initialized. To make an instance of a class you'd normally use a new keyword or if the instance already exists, you want to get it, this.GetComponent<T>() lets you get an existing instance of type T from GameObject that has this script attached to.

errm...I'm having trouble understanding this fully. Ok, so it's a null object to begin with...when I assign rigid via this ->

rigid = GetComponent<Rigidbody>();

do I instantiate something? (or is it initialize??? I'm having a headache right now trying to differentiate between these expressions please guys...help me out) and...well yeah...as u noted: can I get it

it's just that...you express it like this: "you'd normally use" errm...what does this mean? are you suggesting that the above is an optional form of doing it?

When you assign rigid by

rigid = GetComponent<Rigidbody>();

You get existing instance, the instance of Rigidbody was created by Unity in Editor when you added the Rigidbody in the inspector.

3 hours ago, CompuServe said:

it's just that...you express it like this: "you'd normally use" errm...what does this mean? are you suggesting that the above is an optional form of doing it?

I meant, pure classes would be needed to initialize this way

public class SomeClass
{
    public int SomeInteger { get; set; }
}
...
SomeClass mySomeClassVariable; // value is null
mySomeClassVariable = new SomeClass(); // value is new created object of type SomeClass

You don't make this way with Unity's components (Rigidbody, MonoBehaviour) because Unity prefers you to use Unity Editor (inspector), you can initialize it via `AddComponent<Rigidbody>()` tho, it will use make an instance underhood.