ScrollView using Button (NGUI C# UNITY)

Question

I'm having a problem implementing the button to swipe it to the next page I am using NGUI

Here's my script

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

public class NGUI_PageNavigation : MonoBehaviour {

public GameObject sv;
public SpringPanel sp = null;
int xSpring = 1278;
// Use this for initialization
void Start()
{
    sp = sv.GetComponent<SpringPanel>();
    if (sp == null) sv.AddComponent<SpringPanel>();

}

private void OnStoppedMoving()
{

    int pagewidth = 320;
    int pageposition = (int)sp.target.x;
    int page = System.Math.Abs(pageposition / pagewidth) + 1;

    print("page " + (page));
}


public void LeftArrow()
{

    sp.target.x = 1278;
    sp.target.y = 0;
    sp.target.z = 0;
    sp.target = new Vector3(sp.target.x, sp.target.y, sp.target.z);
    sp.enabled = true;

    //Debug.Log("I've been clicked - Left Arrow()");
}

public void RightArrow()
{
    sp.target.x = -1278;
    sp.target.y = 0;
    sp.target.z = 0;
    sp.target = new Vector3(sp.target.x,sp.target.y,sp.target.z);
    sp.enabled = true;
    //Debug.Log("I've been cliked - Right Arrow()");
}
}

it says

NullReferenceException: A null value was found where an object instance was required.

Could someone help me

Answer 1

Take a look at this part of your code:

void Start()
{
    sp = sv.GetComponent<SpringPanel>();
    if (sp == null) sv.AddComponent<SpringPanel>();
}

If GetComponent returns null because SpringPanel is not attached to the sv GameObject, the SpringPanel component will be added to the sv GameObject. The problem is that sp will still be null. You should also assign the value returned by AddComponent to sp.

Replace

if (sp == null) 
    sv.AddComponent<SpringPanel>();

with

if (sp == null) 
    sp = sv.AddComponent<SpringPanel>();