How to block the player from moving left and right from two empty game objects?

Question

I made the game space shooter in that game my spaceship move left and right but its not stop in right and left corner. When its move to left its go out of the screen. how i stop/block in the left and right screen edges.

using UnityEngine;
using System.Collections;

public class PlayerMovement : MonoBehaviour {
    public float speedMove = 3;
    public float bonusTime;
    private Rigidbody rb;
   private float _limit = 3;

    // 1 for right and -1 for left.
    private float _direction = 1;

    // You can call it as speed
    private float _speed = 0.01f;

    private bool toLeft = false;
    private bool toRight = false;

    public GameObject shield;
    public GUIText bonustimeText;

    private bool counting = true;
    private float counter;

    private Weapon[] addWeapons;

    public Sprite strongShip;
    public Sprite normalSprite;
    public Sprite shieldSprite;

    private SpriteRenderer sRender;
    private Weapon weaponScript;

    void Start () {

        counter = bonusTime;
        rb = GetComponent<Rigidbody>();

        sRender = GetComponent<SpriteRenderer> ();
        addWeapons = GetComponentsInChildren<Weapon> ();
        foreach (Weapon addWeapon in addWeapons) {
            addWeapon.enabled = false;
        }

        weaponScript = GetComponent<Weapon>();
        weaponScript.enabled = true;
    }

    // Update is called once per frame
    void Update () {

        transform.position = Vector3.MoveTowards (transform.position,new Vector3 (transform.position.x + _direction, transform.position.y, transform.position.z),_speed);

        if (Input.GetMouseButtonDown (0))
            _direction *= -1;


    }


    void OnCollisionEnter2D(Collision2D coll)
    {
        if (coll.gameObject.tag == "StrongMode") {
            Destroy (coll.gameObject);
            counting = true;
            StrongMode();
            Invoke ("Downgrade", bonusTime);
        }


        if (coll.gameObject.tag == "ShieldMode") {
            Destroy (coll.gameObject);
            counting = true;
            ShieldMode();
            Invoke("Downgrade", bonusTime);
        }

        if (coll.gameObject.tag == "Life") {
            GUIHealth gui = GameObject.Find ("GUI").GetComponent<GUIHealth> ();
            gui.AddHealth();
            SendMessage("AddHp");
            SoundHelper.instanceSound.PickUpSound();
            Destroy(coll.gameObject);
        }

        if (coll.gameObject.tag == "Enemy") {
            SendMessage("Dead");
        }
    }

    void Downgrade()
    {
        SoundHelper.instanceSound.BonusDownSound ();
        counting = false;
        bonustimeText.text = "";
        counter = bonusTime;

        sRender.sprite = normalSprite;
        weaponScript.enabled = true;
        foreach (Weapon addWeapon in addWeapons) {
            addWeapon.enabled = false;
        }
        weaponScript.enabled = true;
        shield.SetActive (false);
    }


    void StrongMode()
    {
        SoundHelper.instanceSound.BonusUpSound ();
        sRender.sprite = strongShip;
        foreach (Weapon addWeapon in addWeapons) {
            addWeapon.enabled = true;
        }
        weaponScript.enabled = false;
    }


    void ShieldMode()
    {
        SoundHelper.instanceSound.BonusUpSound ();
        sRender.sprite = shieldSprite;
        shield.SetActive (true);
    }


//  void OnDestroy()
//  {
//      bonustimeText.text = "";
//  }
}

Answer 1

The easiest solution would probably be to put some box colliders at the edges of the screen. Then collision will prevent your ship from passing through and force it to stay on screen.

Answer 2

Although you could use just box colliders as already suggested, it's pretty much killing a fly with a canon.

A simple approach through code is to compare player's position to camera boundaries position, so if the next position to move to is out of bounds, you don't apply it.

Following this link to the Unity3D forums, you can get an idea of how to get World's position out of screen's.

Then, you just compare the next player's position to corners', and you apply the movement if it won't get out of boundaries.

int leftUpBoundX = x; //Calculate using link
int leftUpBoundY = y; //Same
int movX = -10
int movY = 5
if (playerX + movX >= leftUpBoundX
    && playerY + movY <= leftUpBoundY) {
    playerX += movX;
    playerY += movY;
}

You just do this for the 4 corners and X/Y coords. If you wanted to move in 1 axis even if you can't move in both, you just split X/Y if statements too.

This may seem complicated or CPU consuming but it's actually just adding and comparing integers.

Besides that, have in mind that you can extract this to a common script and use it to both player and/or enemies as well, having no more work than sending the appropiate object's position parameters.