PlayerController File

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PlayerController : MonoBehaviour
{

    public delegate void OnCollectBallAction();
    public OnCollectBallAction OnCollectBall;
    float speed = 600.0f;
    public Camera mainCamera;
    Vector3 leftBound;
    Vector3 rightBound;

    void Start()
    {
      leftBound = mainCamera.ViewportToWorldPoint(new Vector3(0,1, -mainCamera.transform.localPosition.z));
      rightBound = mainCamera.ViewportToWorldPoint(new Vector3(1, 0, -mainCamera.transform.localPosition.z));

    }


    void Update()
    {
        keepInBounds();
        processInput();
        lockPlayerZPosition();
    }

    void lockPlayerZPosition()
    {
        this.transform.position = new Vector3(this.transform.position.x, this.transform.position.y, 0);
    }

    void keepInBounds()
    {
        if(this.transform.position.x < leftBound.x)
        {
            this.transform.position = new Vector3(leftBound.x, this.transform.position.y, this.transform.position.z);
        }
        if(this.transform.position.y > leftBound.y)
        {
            this.transform.position = new Vector3(this.transform.position.x, leftBound.y, this.transform.position.z);
        }
        if(this.transform.position.x > rightBound.x)
        {
            this.transform.position = new Vector3(rightBound.x, this.transform.position.y, this.transform.position.z);
        }
        if(this.transform.position.y < rightBound.y)
        {
            this.transform.position = new Vector3(this.transform.position.x, rightBound.y, this.transform.position.z);
        }

    }

    void processInput()
    {
        if(Input.GetKey("left") || Input.GetKey("a"))
        {
            this.GetComponent<Rigidbody>().AddForce(Vector3.left * speed * Time.deltaTime);
        }
        if(Input.GetKey("right") || Input.GetKey("d"))
        {
            this.GetComponent<Rigidbody>().AddForce(Vector3.right * speed * Time.deltaTime);
        }

    }

    public void OnCollisionEnter (Collision collision)
    {
        if(GetComponent<Collider>().GetComponent<BallController>() != null)
        {
            if(OnCollectBall != null)
            {
                OnCollectBall();
            }
            GameObject.Destroy(GetComponent<Collider>().gameObject);
        }
    }

}