Why is this a null reference exception

Questions & Answers
1

Why is this a null reference exception and how can I fix it. Its on line 44. Thanks!

using UnityEngine;
using System.Collections;

public class BallController : MonoBehaviour {
	public float cSpeed = 15.0f; //Constant speed.

	public float sFactor = 15.0f; //Smoothing factor.

	public static int playerScore = 0; //Holds the current score of the player.

	public static int enemyScore = 0; //Holds the current Enemy's score.

	public Transform target;

	public AudioClip Sfx;

	public float z;


	void Start(){
		GetComponent<Rigidbody>().AddForce(new Vector3(10, 0, 0)); //Initial force to the x-axis to make it move to a direction.
	}
	void Update() {
		PlayerController PC = GetComponent<PlayerController>();
		EnemyController EC = GetComponent<EnemyController>();

		Vector3 cVel = GetComponent<Rigidbody>().velocity;
		Vector3 tVel = cVel.normalized * cSpeed;

		GetComponent<Rigidbody>().velocity = Vector3.Lerp(cVel, tVel, Time.deltaTime * sFactor);

		//Check the boundries on the x-axis.
		if (transform.position.x > 23) {
			enemyScore++; //Increase value by 1;
			GetComponent<Rigidbody>().velocity = new Vector3(10, 0, 0);
			transform.position = new Vector3(0, -16, -20); //Reset ball pos.
			PC.position(-20F, -16F, -19.5F);
			EC.position(20F, -16F, -19.5F);
		}
		if (transform.position.x < -23) {
			playerScore++; //Increase value by 1;
			GetComponent<Rigidbody>().velocity = new Vector3(10, 0, 0);
			transform.position = new Vector3(0, -16, -20); //Reset ball pos.
			PC.position(-20F, -16F, -19.5F);
			EC.position(20F, -16F, -19.5F);
		} 
	}
	void OnGUI() {
		GUI.Label(new Rect(10, 100, 100, 20), "Player 1: " + enemyScore);
		GUI.Label(new Rect(310, 100, 100, 20), "SCORE");
		GUI.Label(new Rect(580, 100, 100, 20), "Player 2: " + playerScore);
	}	
	float hitFactor(Vector3 ballPos, Vector3 racketPos, float racketHeight) {
		return (ballPos.z - racketPos.z) / racketHeight;
	}
	void OnCollisionEnter(Collision collision) {
		GetComponent<AudioSource>().PlayOneShot (Sfx, 0.7F);
		if (collision.gameObject.name == "Player") {
			z = hitFactor(transform.position, collision.transform.position, collision.collider.bounds.size.z);
			Vector3 dir = new Vector3(1, 0, z).normalized;
			GetComponent<Rigidbody>().velocity = dir * cSpeed;
		}

		if (collision.gameObject.name == "Enemy") {
			z = hitFactor(transform.position, collision.transform.position, collision.collider.bounds.size.z);
			Vector3 dir = new Vector3(-1, 0, z).normalized;

			GetComponent<Rigidbody>().velocity = dir * cSpeed;
		}
	}
}
2

What are you trying to do? PC.position(-20F, -16F, -19.5F); would be trying to set the position of a class, which obviously wouldn’t work. I assume PC and EC have a public variable or function in them called position? If so you should really name it something else so it isn’t confused with transform.position.

Which objects are PlayerController and EnemyController on? You are using GetComponent without an object reference so it will be looking for those classes on the same object that this script is on. If it doesn’t also have those scripts on it that will cause a null reference. You need to give it an object reference before the GetComponent.

You should declare them as private variables on start as they are currently local to Update which means OnGUI will not be able to use them.

You should also cache your other references on start so you aren’t constantly using GetComponent.

private Rigidbody rb;
private PlayerController PC;
private PlayerController EC;

void Start()
{
rb = GetComponent<Rigidbody>();

//Add an object reference before GetComponent if these scripts are on another object
PC = GetComponent<PlayerController>();
EC = GetComponent<EnemyController>();
rb.AddForce(new Vector3(10, 0, 0));
}