Overview: Accessing Other Game Objects

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Most advanced game code does not only manipulate a single object. The Unity scripting interface has various ways to find and access other game objects and components there-in. In the following we assume there is a script named OtherScript.js attached to game objects in the scene.

JavaScript

function Update () { 
     var otherScript: OtherScript = GetComponent(OtherScript); 
     otherScript.DoSomething(); 
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Update() {
        OtherScript otherScript = GetComponent<OtherScript>();
        otherScript.DoSomething();
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Update():
        otherScript as OtherScript = GetComponent[of OtherScript]()
        otherScript.DoSomething()

1. Through inspector assignable references.

You can assign variables to any object type through the inspector:

JavaScript

// Translate the object dragged on the target slot

var target : Transform;
function Update () {
    target.Translate(0, 1, 0);
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    public Transform target;
    void Update() {
        target.Translate(0, 1, 0);
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public target as Transform

    def Update():
        target.Translate(0, 1, 0)

You can also expose references to other objects to the inspector. Below you can drag a game object that contains the OtherScript on the target slot in the inspector.

JavaScript

// Set foo DoSomething on the target variable assigned in the inspector.

var target : OtherScript;

function Update () {
    // Set foo variable of the target object
    target.foo = 2;
    // Call do something on the target
    target.DoSomething("Hello");
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    public OtherScript target;
    void Update() {
        target.foo = 2;
        target.DoSomething("Hello");
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public target as OtherScript

    def Update():
        target.foo = 2
        target.DoSomething('Hello')

2. Located through the object hierarchy.

You can find child and parent objects to an existing object through the Transform component of a game object:

JavaScript

// Find the child "Hand" of the game object 
// we attached the script to

transform.Find("Hand").Translate(0, 1, 0);

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Example() {
        transform.Find("Hand").Translate(0, 1, 0);
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Example():
        transform.Find('Hand').Translate(0, 1, 0)

Once you have found the transform in the hierarchy, you can use GetComponent to get to other scripts.

JavaScript

// Find the child named "Hand".
// On the OtherScript attached to it, set foo to 2.
transform.Find("Hand").GetComponent(OtherScript).foo = 2;

// Find the child named "Hand".
// Call DoSomething on the OtherScript attached to it.
transform.Find("Hand").GetComponent(OtherScript).DoSomething("Hello");

// Find the child named "Hand".
// Then apply a force to the rigidbody attached to the hand.
transform.Find("Hand").rigidbody.AddForce(0, 10, 0);

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Example() {
        transform.Find("Hand").GetComponent<OtherScript>().foo = 2;
        transform.Find("Hand").GetComponent<OtherScript>().DoSomething("Hello");
        transform.Find("Hand").rigidbody.AddForce(0, 10, 0);
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Example():
        transform.Find('Hand').GetComponent[of OtherScript]().foo = 2
        transform.Find('Hand').GetComponent[of OtherScript]().DoSomething('Hello')
        transform.Find('Hand').rigidbody.AddForce(0, 10, 0)

You can loop over all children:

JavaScript

// Moves all transform children 10 units upwards!

for (var child : Transform in transform) {
    child.Translate(0, 10, 0);
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Example() {
        foreach (Transform child in transform) {
            child.Translate(0, 10, 0);
        }
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Example():
        for child as Transform in transform:
            child.Translate(0, 10, 0)

See the documentation for the Transform class for further information.

3. Located by name or Tag.

You can search for game objects with certain tags using GameObject.FindWithTag and GameObject.FindGameObjectsWithTag. Use GameObject.Find to find a game object by name.

JavaScript

function Start () {
    // By name
    var go = GameObject.Find("SomeGuy");
    go.transform.Translate(0, 1, 0);

    // By tag
    var player = GameObject.FindWithTag("Player");
    player.transform.Translate(0, 1, 0);
    
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Start() {
        GameObject go = GameObject.Find("SomeGuy");
        go.transform.Translate(0, 1, 0);
        GameObject player = GameObject.FindWithTag("Player");
        player.transform.Translate(0, 1, 0);
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Start():
        go as GameObject = GameObject.Find('SomeGuy')
        go.transform.Translate(0, 1, 0)
        player as GameObject = GameObject.FindWithTag('Player')
        player.transform.Translate(0, 1, 0)

You can use GetComponent on the result to get to any script or component on the found game object

JavaScript

function Start () {
    // By name
    var go = GameObject.Find("SomeGuy");
    go.GetComponent(OtherScript).DoSomething();

    // By tag
    var player = GameObject.FindWithTag("Player");
    player.GetComponent(OtherScript).DoSomething();
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Start() {
        GameObject go = GameObject.Find("SomeGuy");
        go.GetComponent<OtherScript>().DoSomething();
        GameObject player = GameObject.FindWithTag("Player");
        player.GetComponent<OtherScript>().DoSomething();
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Start():
        go as GameObject = GameObject.Find('SomeGuy')
        go.GetComponent[of OtherScript]().DoSomething()
        player as GameObject = GameObject.FindWithTag('Player')
        player.GetComponent[of OtherScript]().DoSomething()

Some special objects like the main camera have shorts cuts using Camera.main.

4. Passed as parameters.

Some event messages contain detailed information on the event. For instance, trigger events pass the Collider component of the colliding object to the handler function.

OnTriggerStay gives us a reference to a collider. From the collider we can get to its attached rigidbody.

JavaScript

function OnTriggerStay( other : Collider ) {
    // If the other collider also has a rigidbody
    // apply a force to it!
    if (other.rigidbody)
        other.rigidbody.AddForce(0, 2, 0);
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void OnTriggerStay(Collider other) {
        if (other.rigidbody)
            other.rigidbody.AddForce(0, 2, 0);
        
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def OnTriggerStay(other as Collider):
        if other.rigidbody:
            other.rigidbody.AddForce(0, 2, 0)

Or we can get to any component attached to the same game object as the collider.

JavaScript

function OnTriggerStay( other : Collider ) {
    // If the other collider has a OtherScript attached
    // call DoSomething on it.
    // Most of the time colliders won't have this script attached,
    // so we need to check first to avoid null reference exceptions.
    if (other.GetComponent(OtherScript))
        other.GetComponent(OtherScript).DoSomething();
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void OnTriggerStay(Collider other) {
        if (other.GetComponent<OtherScript>())
            other.GetComponent<OtherScript>().DoSomething();
        
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def OnTriggerStay(other as Collider):
        if other.GetComponent[of OtherScript]():
            other.GetComponent[of OtherScript]().DoSomething()

Note that by suffixing the other variable in the above example, you can access any component inside the colliding object.

5. All scripts of one Type

Find any object of one class or script name using Object.FindObjectsOfType or find the first object of one type using Object.FindObjectOfType.

JavaScript

function Start () {
    // Find the OtherScript which is attached to any game object in the scene.
    var other : OtherScript = FindObjectOfType(OtherScript);
    other.DoSomething();
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Start() {
        OtherScript other = FindObjectOfType(typeof(OtherScript));
        other.DoSomething();
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Start():
        other as OtherScript = FindObjectOfType(OtherScript)
        other.DoSomething()

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