# OnCollisionEnter2D(Collision2D)

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

## Definition

* **Type:** Method
* **Namespace:** [UnityEngine](/engine/6000.6/script-reference/unityengine.md)

## OnCollisionEnter2D()

```csharp
public void OnCollisionEnter2D(Collision2D collision2D)
```

### Parameters

**** (\[Collision2D]\(/engine/6000.6/script-reference/unityengine/collision2d)): 

### Remarks

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:** OnCollisionEnter2D is only called on scripts attached to GameObjects that have a Collider2D and/or Rigidbody2D directly involved in the collision. It is not automatically passed up to parent GameObjects unless they themselves have the relevant components. Compound colliders (parent Rigidbody2D + child Collider2Ds) receive events on both the parent and the specific child involved. Collision events are sent to disabled MonoBehaviours, to allow enabling Behaviours in response to collisions. Additional Resources: [Collision2D](/engine/6000.6/script-reference/unityengine/collision2d.md) class, OnCollisionExit2D, OnCollisionStay2D. The following 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.

### Examples

```csharp

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");
    }
}
```