NullReferenceException : Object reference not set to an instance of an object

i am making a new 2d game using unity and C# scripting. i got an error that containt this message.
NullReferenceException: Object reference not set to an instance of an object
CharLayer.Update () (at Assets/CharLayer.cs:24)
these are my codes

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3.  
4. public class CharLayer : MonoBehaviour {
5.     public GameObject treeGO;
6.     private TreeScript treeScript;
7.     private float positionChar;
8.     public const string LAYER_NAME = "ForeGround";
9.     public const string LAYER_BACK = "Character";
10.     public int sortingOrder = 0;
11.     private SpriteRenderer sprites;
12.  
13.  
14.     // Use this for initialization
15.     void Start () {
16.         treeScript = GetComponent<TreeScript> ();
17.         sprites = GetComponent<SpriteRenderer>();
18.     }
19.     // Update is called once per frame
20.     void Update () {
21.         positionChar = rigidbody2D.velocity.y;
22.         if (treeScript.TreePos < positionChar)
23.         {
24.             sprites.sortingOrder = sortingOrder;
25.             sprites.sortingLayerName = LAYER_NAME;
26.         }
27.         else if (treeScript.TreePos > rigidbody2D.velocity.y)
28.         {
29.             sprites.sortingOrder = sortingOrder;
30.             sprites.sortingLayerName = LAYER_BACK;
31.         }
32.     }
33. }

and another one

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3.  
4. public class TreeScript : MonoBehaviour {
5.     public float TreePos;
6.     // Use this for initialization
7.     void Start () {
8.         TreePos = transform.localScale.y;
9.  
10.     }
11.     // Update is called once per frame
12.     void Update () {
13.     }
14. }

what's wrong with my code, please help. i'm sorry, my english is so bad.

 

If you want someone to spend time helping you with a problem, spend time using Code Tags so that what you post is more readable.

As for your error, it means your trying to access something on an object that is missing or not linked correctly. In this case, I'd imagine one of your GetCompenent calls is falling to find something and your later trying to access it (treeScript or sprites)

 

thanks NomadKing, i've edited my thread.