Object Reference Error when passing a Dictionary - Help?

I am trying to pass a dictionary from one script to another to then write into the dictionary in the second script via a trigger. The initialization worked (I added using System.Collections.Generic, but when I pass the Dictionary I get an error. Odd thing is that when I do the same thing with a list, I have no problem. Here is the error:

Code (csharp):

1. NullReferenceException: Object reference not set to an instance of an object
2.  

Here is my initialization of my dictionary and list in the first script called NN_PositionNode:

Code (csharp):

1.  
2. public List<NN_PositionNode> connectedPositionList = new List<NN_PositionNode>();
3. public Dictionary<int,float> distanceToPositionDic = new Dictionary<int,float>();    

Here is the Code from my second script:

Code (csharp):

1.  
2. void OnTriggerEnter (Collider other)
3.     {  
4.         NN_PositionNode NN_CurrentNode = other.gameObject.GetComponent<NN_PositionNode>();     
5.        
6.         MyPositionNode.connectedPositionList.Add(NN_CurrentNode);  
7.   MyPositionNode.distanceToPositionDic.Add(NN_CurrentNode.myID,Vector3.Distance(this.transform.position,other.transform.position));
8.             }
9.        

Anyone have any thoughts?

Thanks!

 

Need to know which line the error occurred on but my guess is that your "other" collider doesn't have an NN_PositionNode component so your GetComponent call is returning null. Attach the debugger and set a breakpoint there and step through, see what's happening.

 

Hmm. Well, what is odd is that I have a list in the NN_PositionNode (the same script as the dictionary) that is passed and updated just fine. It is there in the code I put above. The error is on the dictionary line in the collider, not on the list line, which works fine. I will Log the position node and see what happens. If you have any other ideas, please let me know. Thanks!

 

NN_PositionNode NN_CurrentNode = other.gameObject.GetComponent<NN_PositionNode>();
This line is not getting a NN_PositionNode, so the currentnode variable is null
Check what the colliding object is.

 

@hpjohn, the line is actually getting a NN_PositionNode because I am able to add to a list from that script. I just can't seem to add to the dictionary. The following line is from that same script and it works fine:

MyPositionNode.connectedPositionList.Add(NN_CurrentNode);


I am really at a loss. Why would the dictionary return null while the list does not?

 

Show us the whole error. Highlight it in the console and give us the whole stack trace, or just the first 3 or 4 lines if it's a long one.

 

You are still not getting my point

Code (csharp):

1.     class myClass {
2.         public int id;
3.     }
4.  
5.     List<myClass> aList = new List<myClass>();
6.     Dictionary<int, float> aDict = new Dictionary<int, float>();
7.  
8.     void Start () {
9.         myClass newClass = new myClass();   //make or get an instance of myClass
10.         aList.Add( newClass );              //add to list ##WORKS##
11.         aDict.Add( newClass.id, 5f );       //get property from instance, and add to dict using it ##WORKS##
12.  
13.         myClass anotherNewClass = null;     //try to get an instance that is null
14.                                             //(eg. via getcomponent on a GO that doesnt have component)
15.         aList.Add( anotherNewClass );       //add null reference to list ##WORKS##
16.         aDict.Add( anotherNewClass.id, 5f );//get property from a null reference ##DONT WORK##
17.     }
18.  

when the instace of a class is null, you cannot pull properties from it.
your other.gameObject.GetComponent<NN_PositionNode>(); is probably not finding a NN_PositionNode, so the reference is null, and properties do not exist

 

Angry Penguin:

Code (csharp):

1. NullReferenceException: Object reference not set to an instance of an object ListConnections.OnTriggerEnter (UnityEngine.Collider other) (at Assets/Neural Net Scripts/ListConnections.cs:45) .

The line is the dictionary.add line.

hpjohn: I believe I do understand what you are saying. What is weird is that I can debug.log a dictionary declared in both this script and another script without a problem, but then if I .add to the dictionary, all of a sudden I get a NULL reference:

This is how I reference the script:

Code (csharp):

1. MyPositionNode = MyNodeObject.GetComponent<NN_PositionNode>(); 

This is in the collider and works:

Code (csharp):

1.  
2.             NN_PositionNode NN_CurrentNode = other.gameObject.GetComponent<NN_PositionNode>();     
3.             Debug.Log("Node Dic:" + NN_CurrentNode.distanceToPositionDic);
4.  

However, if I try to add to the dictionary as below, then I get the error above:

Code (csharp):

1. MyPositionNode.distanceToPositionDic.Add(CurrentNode.myID,Vector3.Distance(this.transform.position,other.transform.position));

This doesn't happen with a list. I might be misunderstanding you, but I don't understand why I can add to a list, but not to a dictionary of the same script. I am also referencing a script from the "other" object, and a script on the parent of this script which is allocated like this:

Code (csharp):

1.  
2. if (MyNodeObject == null)   //if the programmer hasn't set the node object, then this can be done automatically via this script
3.         {
4.             try
5.             {
6.                 MyNodeObject = this.transform.parent.gameObject;
7.             }
8.             catch
9.             {
10.                 Debug.LogError("Parent isn't a Node");
11.             }
12.         }
13.  

This doesn't throw an error either... ugh. I read what you sent me and I am pretty sure I am understanding what you are saying and have done that properly. Why would it not a throw an error when I just log the dictionary, but then log an error when I try to add to it? the distance formula works fine in the list as well.