Accessing a script from another script at runtime in Unity C#

Question

Like in here, but the difference is that it's supposed to be done from an instantiated prefab, so I can not drag the GameObject, that has the script with the variable I want to access, into this script.

This was working

public ScriptA script;

void Update() {
   if (script.varX < 0) {
      // . . .
   }
}

But now I'm getting "Object reference not set to an instance of an object" error, which I think comes from the fact that the script trying to access ScriptA, is attached to an instantiated prefab.

How do I attach scripts and/or GameObjects at runtime?

Possible duplicate of Accessing a variable from another script C# — Draco18s no longer trusts SE
– Draco18s no longer trusts SE, Commented Mar 12, 2018 at 19:33
It's not a duplicate. I linked that same question in my post, the difference is that I need to access the other script from a prefab GameObject, it can't be done in the same way. — RealAnyOne
– RealAnyOne, Commented Mar 13, 2018 at 0:08
You instantiate a prefab and then with a reference to that clone, given to you by the instantiate method, you....do the thing listed in the dupe target... — Draco18s no longer trusts SE
– Draco18s no longer trusts SE, Commented Mar 13, 2018 at 0:51

Tom · Accepted Answer · 2018-03-12 14:28:22Z

1

Looks like you need to find your script type first, if it already exists in the scene:

public ScriptA script;

void Start()
{
    script = GameObject.FindObjectOfType<ScriptA>();
}

void Update()
{
    if(script.variable...)
}

answered Mar 12, 2018 at 14:28

Tom

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2 Comments

RealAnyOne Over a year ago

Why FindObjectOfType and not just .Find or any of the others?

Tom Over a year ago

@RealAnyOne Find returns a GameObject (maybe other objects, I'm unsure) where as FindObjectOfType finds the type you are searching for, in this case ScriptA. It's safer and quicker than doingGameObject.Find("YourGameObject").GetComponent<ScriptA>() Another useful one is FindObjectsOfType which is plural, so you can populate an array of ScriptA types that way, like ScriptA[] scripts = GameObject.FindObjectsOfType<ScriptA>()

user2936032 · Accepted Answer · 2018-03-12 14:22:05Z

1

You want to use AddComponent, like:

ScriptA script = gameObject.AddComponent<ScriptA>() as ScriptA;

See the docs here: https://docs.unity3d.com/ScriptReference/GameObject.AddComponent.html

answered Mar 12, 2018 at 14:22

user2936032

4 Comments

Basile Perrenoud Over a year ago

you don't need as ScriptA

RealAnyOne Over a year ago

What about attaching a GameObject to the instantiated Prefab? :P

user2936032 Over a year ago

Assuming the GameObject has already been instantiated, you can use GameObject's Find, FindWithTag, FindObjectOfType, FindObjectsOfType to (hopefully) locate it

RealAnyOne Over a year ago

As to the direct answer to my post: ScriptA script = gameObject.AddComponent<ScriptA>() as ScriptA; actually adds that script to the gameobject, when I only wanted to access and change some variables. I'll look more into what I have and maybe edit my first post to be clearer, maybe it was my fault in explaining

zambari · Accepted Answer · 2018-03-16 15:52:53Z

0

Best way to satify the links is fill the fields in the very next lines after you instantiate, that way you can avoid ugly and expenstive Find* calls (I am assuming the script that does the instancing can be made aware of what the target objects are, after all it knows what and where to instantiate)

Its worth noting that newly instantiated scripts' Awake() method will be called before Instantiate() returns, while its Start() will be called at the start of following frame, this is a major difference between the two calls, so if your instantiated script needs the refectences in Awake() you should either refactor (move stuff to Start()) or use Find* as suggested earlier.

answered Mar 16, 2018 at 15:52

zambari

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