How to get a Collision2D Name that is in a brackets after a function name from another script in c#?

Questions & Answers
1

void OnCollisionEnter2D (Collision2D collision){

        //I want access this -------↑ from another script,How to do it?

}

2

You’ll set an identifier and expose it either by setting its access modifier public, or encapsulating it in a property and exposing it that way.

Field using public access:

using UnityEngine;

public class ExampleClass : MonoBehaviour {
    public Collision2D m_collision;

    void OnCollisionEnter(Collision2D collision) {
        m_collision = collision;
    }
}

Property example:

using UnityEngine;

public class ExampleClass : MonoBehaviour {
    private Collision2D m_collision = null;

    void OnCollisionEnter(Collision2D collision) {
        m_collision = collision;
    }

    public Collision2D MyCollision { get { return m_collision; } }
}

In the other class, you’ll have to get a reference to ExampleClass in this case in order to access the identifier:

using UnityEngine;

public class SomeOtherExampleClass : MonoBehaviour {    
    void Start() {

        // From the public field access
        if (FindObjectOfType<ExampleClass>().m_collision)
            Debug.Log(FindObjectOfType<ExampleClass>().m_collision);
        else
            Debug.Log("Collision data was null");

        // From the property access
        if (FindObjectOfType<ExampleClass>().MyCollision)
            Debug.Log(FindObjectOfType<ExampleClass>().MyCollision);
        else
            Debug.Log("Collision data was null");
    }
}

The search method is up to you, depending on how you have your hierarchy set up. FindObjectOfType<T> is rather expensive. GetComponent<T> is less so, GetComponentInChildren<T> is marginally slower than GetComponent<T>, etc. I can’t remember if a Collision object can be assigned a null value. If it can’t, initialize it as a new Collision object and in the conditional, check for MyCollision or m_collision being equal to a new Collision object if the script you have OnCollision2D hasn’t run yet.