Trouble with assigning/generating Physics material

I've been trying to work out how to attach or set the physics materials bounciness/friction, I know it's this: gameObject.GetComponent<BoxCollider2D> ().sharedMaterial.bounciness = 1f;

But I keep getting an error, "object reference not set to an instance of an object" and I don't quite know why, is it to do with not assigning a Physics material to the object and trying to set something that's not there? I don't really know how to assign a physics material to the collider when doing it generatively.

Has anyone got any ideas?

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3. using System.Collections.Generic;
4.  
5. public class GenerateColliders : MonoBehaviour
6. {
7.  
8.     public float widthOfCollider = 2f;
9.     public float z_axis = 0f;
10.     private Vector2 screenSize;
11.  
12.     void Start ()
13.     {
14.         Dictionary<string,Transform> colliders = new Dictionary<string,Transform>();
15.         //Create GameObjects and add their Transform components to the Dictionary created above
16.         colliders.Add("Top",new GameObject().transform);
17.         colliders.Add("Bottom",new GameObject().transform);
18.         colliders.Add("Right",new GameObject().transform);
19.         colliders.Add("Left",new GameObject().transform);
20.  
21.         Vector3 cameraPos = Camera.main.transform.position;
22.         screenSize.x = Vector2.Distance (Camera.main.ScreenToWorldPoint(new Vector2(0,0)),Camera.main.ScreenToWorldPoint(new Vector2(Screen.width, 0))) * 0.5f;
23.         screenSize.y = Vector2.Distance (Camera.main.ScreenToWorldPoint(new Vector2(0,0)),Camera.main.ScreenToWorldPoint(new Vector2(0, Screen.height))) * 0.5f;
24.  
25.                     //loop through the transforms in colliders
26.             foreach(KeyValuePair<string,Transform> bc in colliders)
27.             {
28.                        //Add the collider component
29.                     bc.Value.gameObject.AddComponent<BoxCollider2D>();
30.  
31.                     bc.Value.gameObject.GetComponent<BoxCollider2D> ().sharedMaterial.bounciness = 1f;
32.  
33.                     bc.Value.gameObject.GetComponent<BoxCollider2D> ().sharedMaterial.friction = 1f;
34.  
35.                     //give the objects a name
36.                     bc.Value.name = bc.Key + "Collider";
37.                       //Make the object with collider child of the object this script is attached to
38.                     bc.Value.parent = transform;
39.                        //Scale the object to the width and height of the screen
40.                     if(bc.Key == "Left" || bc.Key == "Right")
41.                         bc.Value.localScale = new Vector3(widthOfCollider, screenSize.y * 2, widthOfCollider);
42.                     else
43.                         bc.Value.localScale = new Vector3(screenSize.x * 2, widthOfCollider, widthOfCollider);
44.             }
45.                 colliders["Right"].position = new Vector3(cameraPos.x + screenSize.x + (colliders["Right"].localScale.x * 0.5f), cameraPos.y, z_axis);
46.             colliders["Left"].position = new Vector3(cameraPos.x - screenSize.x - (colliders["Left"].localScale.x * 0.5f), cameraPos.y, z_axis);
47.         colliders["Top"].position = new Vector3(cameraPos.x, cameraPos.y + screenSize.y + (colliders["Top"].localScale.y * 0.5f), z_axis);
48.         colliders["Bottom"].position = new Vector3(cameraPos.x, cameraPos.y - screenSize.y - (colliders["Bottom"].localScale.y * 0.5f), z_axis);
49.     }
50. }

 

Unless you already have one assigned, it will indeed be null.
Making a new one is simple;
http://docs.unity3d.com/ScriptReference/PhysicMaterial-ctor.html

 

Thanks I was just being dumb! I worked it out, was just coming back on to say!

public physicsmaterial2d mat;
and then shared material = mat;

Gets late and sometimes the simplest things mess me up!