MonoBehaviour.OnCollisionEnter2D(Collision2D)

Parameters

Description

Sent when an incoming collider makes contact with this object's collider (2D physics only).

Further information about the collision is reported in the Collision2D parameter passed during the call. If you don't need this information then you can declare OnCollisionEnter2D without the parameter.

Note: Collision events will be sent to disabled MonoBehaviours, to allow enabling Behaviours in response to collisions.

Additional resources: Collision2D class, OnCollisionExit2D, OnCollisionStay2D.

The folllowing two script examples create an OnCollisionEnter2D demo. Example1 generates a (white) box sprite called GameObject1. This sprite collides with the Example2 GameObject2 which is the floor sprite. The box sprite can be moved using the up, down, left and right keys. For example, once the box has fallen to the floor it can be pushed upwards with the up key. Once the up key is released the box will fall back to the floor. Each time the box hits the floor an OnCollisionEnter2D call will be made. GameObject1 simply provides a string in the console to indicate the collision has happened.

using UnityEngine;

// Create a box sprite which falls and hits a floor sprite.  The box can be moved/animated
// with the up, left, right, and down keys.  Moving the box sprite upwards and letting it
// fall will increase the number of calls from OnCollisionEnter2D.

public class Example1 : MonoBehaviour
{
    public Texture2D tex;

    void Awake()
    {
        SpriteRenderer sr = gameObject.AddComponent<SpriteRenderer>() as SpriteRenderer;
        transform.position = new Vector3(0.0f, 2.5f, 0.0f);

        Sprite sp = Sprite.Create(tex, new Rect(0.0f, 0.0f, tex.width, tex.height), new Vector2(0.5f, 0.5f), 100.0f);
        sr.sprite = sp;

        gameObject.AddComponent<BoxCollider2D>();

        Rigidbody2D rb = gameObject.AddComponent<Rigidbody2D>();
        rb.bodyType = RigidbodyType2D.Dynamic;
    }

    void FixedUpdate()
    {
        float moveHorizontal = Input.GetAxis("Horizontal");
        float moveVertical = Input.GetAxis("Vertical");

        gameObject.transform.Translate(moveHorizontal * 0.05f, moveVertical * 0.25f, 0.0f);
    }

    // called when the cube hits the floor
    void OnCollisionEnter2D(Collision2D col)
    {
        Debug.Log("OnCollisionEnter2D");
    }
}

Example2. This creates the floor.

using UnityEngine;

public class Example2 : MonoBehaviour
{
    public Texture2D tex;

    void Awake()
    {
        SpriteRenderer sr = gameObject.AddComponent<SpriteRenderer>() as SpriteRenderer;
        transform.position = new Vector3(0.0f, -2.0f, 0.0f);

        Sprite sp = Sprite.Create(tex, new Rect(0.0f, 0.0f, tex.width, tex.height), new Vector2(0.5f, 0.5f), 100.0f);
        sr.sprite = sp;

        gameObject.AddComponent<BoxCollider2D>();
    }
}

The two objects are stored as GameObjects each with one of the scripts. These GameObjects start with just the script example that it needs. Example1 is applied to GameObject1 and Example2 to GameObject2.