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

The error message says the problem is at line 21. I have a number of panels with an image that I drag and drop into another panel. Every time I try to drag from one panel to the other in play mode, I get the error message.

Code (CSharp):

1. using System.Reflection;
2. using UnityEngine;
3. using UnityEngine.EventSystems;
4. using UnityEngine.UI;
5.  
6. public class DropMe : MonoBehaviour, IDropHandler, IPointerEnterHandler, IPointerExitHandler
7. {
8.     public Image containerImage;
9.     public Image receivingImage;
10.     private Color normalColor;
11.     public Color highlightColor = Color.yellow;
12.    
13.     public void OnEnable ()
14.     {
15.         if (containerImage != null)
16.             normalColor = containerImage.color;
17.     }
18.    
19.     public void OnDrop(PointerEventData data)
20.     {
21.             containerImage.color = normalColor;
22.        
23.        
24.         if (receivingImage == null)
25.             return;
26.        
27.         Sprite dropSprite = GetDropSprite (data);
28.         if (dropSprite != null)
29.             receivingImage.overrideSprite = dropSprite;
30.     }
31.  
32.     public void OnPointerEnter(PointerEventData data)
33.     {
34.         if (containerImage == null)
35.             return;
36.        
37.         Sprite dropSprite = GetDropSprite (data);
38.         if (dropSprite != null)
39.             containerImage.color = highlightColor;
40.     }
41.  
42.     public void OnPointerExit(PointerEventData data)
43.     {
44.         if (containerImage == null)
45.             return;
46.        
47.         containerImage.color = normalColor;
48.     }
49.    
50.     private Sprite GetDropSprite(PointerEventData data)
51.     {
52.         var originalObj = data.pointerDrag;
53.         if (originalObj == null)
54.             return null;
55.        
56.         var dragMe = originalObj.GetComponent<DragMe>();
57.         if (dragMe == null)
58.             return null;
59.        
60.         var srcImage = originalObj.GetComponent<Image>();
61.         if (srcImage == null)
62.             return null;
63.        
64.         return srcImage.sprite;
65.     }
66. }
67.  

 

Seems like you need a null check at line 20.

 

That's what I thought originally too, I already tried

Code (CSharp):

1.         if(normalColor != null)
2.             containerImage.color = normalColor;

but I got the same error message.

 

normalColor isn't the thing you need to null check. containerImage is the one that would be causing the issue.

 

Thank you. My compiler issues are fixed. Now I can fix the other problems.