Function gives NullReferenceException after running through succesfully once.

Hello everyone.

In Unityscript, I have a function to pick a random string out of an array, and this function is called in a foreach loop, but it returns a NullReferenceException. I printed to the console to have a look, and it's running through the foreach loop once, picking the random string, and on the second go through it's giving me the error.

This is the relevant parts of the code, with Module and ModuleConnector being scripts on an object and it's children, respectively:

Code (JavaScript):

1. import System.Collections.Generic;
2. import System.Linq;
3.  
4. var modules  :  GameObject[];
5. var startModule  :  GameObject;
6.  
7. var iterations       =   5;
8.  
9. function Start ()
10. {
11.    var startModule = Instantiate(startModule, transform.position +Vector3(0,40,0), transform.rotation);
12.    var pendingExits = new Array(startModule.GetComponent(Module).GetExits());
13.  
14.    for (var iteration = 0; iteration < iterations; iteration++)
15.    {
16.      var newExits = new List.<ModuleConnector>();
17.  
18.      for(var pendingExit:ModuleConnector in pendingExits)
19.      {
20.        var newTag       =   GetRandom(pendingExit.connectorTags);
21.          print(newTag);
22.        var newModuleObject =   GetRandomWithTag(modules, newTag);
23.        var newModulePrefab   :   GameObject = newModuleObject;   //This is to convert the object to a GameObject so I can access it's components.
24.        var newModule     =   Instantiate(newModulePrefab);
25.      }
26.    }
27. }
28.  
29. function GetRandom(randomArray:Array)
30. {
31.    return randomArray[Random.Range(0, randomArray.length)];
32. }
33.  
34. function GetRandomWithTag(modules:GameObject[],tagToMatch:String)     //Fetches a random module that has matching tags
35. {
36.    var matchingModules   :   GameObject[];
37.  
38.    for(var i=0; i < modules.Length; i++)
39.    {
40.      if (modules[i].GetComponent(Module2).moduleTags.Contains(tagToMatch))
41.      {
42.        matchingModules[i] =  modules[i];   //This is the line that throws the exception.
43.      }
44.    }
45.    return GetRandom(matchingModules);
46. }
47.  

If it's relevant, this is the code for the GetExits() function in the Module script:

Code (JavaScript):

1. function GetExits()
2. {
3.     return GetComponentsInChildren(ModuleConnector);
4. }

I had something similar to this working a while back in C#, but I clearly need to catch up as far as Unityscript goes. I'd really appreciate the help if someone could point me in the right direction and let me know where I went wrong.

 

Code (CSharp):

1. function GetRandom(randomArray:Array)
2. {
3.    return randomArray[Random.Range(0, randomArray.length)];
4. }

Shouldn't it be randomArray.length - 1?
Random.Range(min, max) has min and max both inclusive, I believe.

 

"The returned value will never be max unless min equals max."

From the documentation

 

That is correct only when it is Random.Range(int, int).
Which is true in this case.
I did not know int and float Random.Range are different, my bad, thanks for pointing out my mistake!

 

I had a look at that function earlier, when I was trying to figure out what was going on. GetRandom() works without any issues though, and the error isn't pointing at that line (though that's not always an accurate measure of the problem).

 

Then what line does it say it fails at?
NullReferenceException means that a null value is being accessed.
Either use the debugger, or just print every value (or at least it's size) and see where it get stuck.

 

I added a note in the code detailing the line that throws the exception, but I probably should have mentioned this outside of the posted code, as well.
It's here, in any case, the line inside the if statement:

Code (JavaScript):

1. function GetRandomWithTag(modules:GameObject[],tagToMatch:String)     //Fetches a random module that has matching tags
2. {
3.    var matchingModules   :   GameObject[];
4.    for(var i=0; i < modules.Length; i++)
5.    {
6.      if (modules[i].GetComponent(Module2).moduleTags.Contains(tagToMatch))
7.      {
8.        matchingModules[i] =  modules[i];   //This is the line that throws the exception.
9.      }
10.    }
11.    return GetRandom(matchingModules);
12. }

 

My bad, I did not notice that part.
I am not much of a JS coder, but is it okay to access matchingModules before declaring matchingModules = new GameObject[modules.length] ?

 

No worries, I didn't realize before posting the code that it'd be that subtle and difficult to notice. It doesn't exactly stand out.

While your suggestion wasn't the problem, it was the catalyst for my changing things that led to a series of errors that, in the end, allowed me to figure it out. =P

I'd forgotten that GameObject[], as a builtin array, had the size I initially set and that size wasn't inclined to change, so a majority of the entries in that array were null.

I ended up making a normal array with a length of 0, then increased it's length by 1 for each module that had the correct tag, before assigning that module to the array.

Thanks for all your help. =)

 

Glad you managed to have it work