How do I add a NetworkView to other classes?

How do I add a NetworkView to other classes?
I have some problem with calling the [command] and [clientrpc] on any classes in my scripts.

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using UnityEngine.Networking;
5.  
6. public class Sync : MonoBehaviour {
7.     public bool position, rotation, child;
8.     public bool syncChildTransform,syncChildRotation;
9.     public GameObject[] childObjs;
10.     Sync_NetManager sync = new Sync_NetManager();
11.     NetworkIdentity id;
12.     void Update(){
13.         if (id == null)
14.             id = transform.GetComponent<NetworkIdentity>();
15.         if (!sync.isLocal(id))
16.             return;
17.         if(child)
18.         sync.SetChildObjects(childObjs);
19.        
20.         SyncManager();
21.     }
22.     private void SyncManager(){
23.         if (transform) {
24.             if (child) {
25.                
26.             } else {
27.                 sync.CmdSync(1,2,transform.position,transform.rotation);
28.             }
29.         }
30.         if (rotation) {
31.             if (child) {
32.                
33.             } else {
34.                 sync.CmdSync(2,2,transform.position,transform.rotation);
35.             }
36.         }
37.     }
38. }
39.  
40.  
41.  
42. public class Sync_NetManager : NetworkBehaviour {
43.     private GameObject[] _childObjs;
44.  
45.     public bool isLocal(NetworkIdentity id){
46.         return id.isLocalPlayer;
47.     }
48.     public void SetChildObjects(GameObject[] childObjs){
49.         this._childObjs = childObjs;
50.     }
51.  
52.     [Command]
53.     public void CmdSync(int type, int num, Vector3 pos, Quaternion rot){
54.         RpcSync(type,num,pos,rot);
55.     }
56. }

Error:
NullReferenceException
UnityEngine.Component.GetComponent[NetworkIdentity];
How can I solve it?