Am I having Variable Scope issues?

Question

I am writing in Unity and not all classes can be instantiated as they inheriting Monobehaviour. I have several classes and am trying to Return an array to one class, but keep getting a null reference exception. I have made sure the array is indexed and initialized, yet it returns null. However in a same construction without an array, eg an Int, it works.

public class StartUp : MonoBehaviour  //Unity class
{
        public int x = 30,y = 30;
        public PlayField entireField;

        void Awake()
        {
            entireField = new PlayField(x,y);
            entireField.InitArray(entireField, x, y);
        }
}

public class CharacterController : MonoBehaviour
{
       //edit: playField is not supposed hold value, just to get
       //access to a method in PlayField
       PlayField playField; 

       FieldData fData;           

       void Start(){
           playField = new PlayField();
           fData = new FieldData();
       }
       void Update(){
          fData = playField.GetFieldData(5,6); //We're just telling it go to that method 
       } 
}
public class PlayField
{
       public SingleField[,] singleField;

       public PlayField()
       {

       }
       public PlayField(int x, int y)
       {
              singleField = new SingleField[x,y];
       }

       void InitArray(PlayField playfield, int x, int y){
              //In an effort to save the data I also did
              this.singleField = new SingleField[x,y];

              for(int j ...
              {
                  for (int x...
                  {
                      playfield.singleField[x, y] = new SingleField();
                      playfield.singleField[x, y].fielData = new FieldData();
                      playfield.singleField[x, y].fielData.height = GetRandom();
                      //and here
                      this.singleField[x,y] = new SingleField();
                      this.singleField[x,y].fieldData = new FieldData();
                  }
              }
              //to ..
              this.singleField = playfield.singleField;
       }

       public FieldData GetFieldData(int x, int y){

            //Here it keeps returning null reference
            return this.singleField[x,y].fieldData;
       }
}

public class SingleField
{
       public FieldData fieldData;
       public GameObject fieldObject;
}
public class FieldData
{
        public float height;
        public Vector3 position = new Vector3();
}

I know I can use a static variable but I'd like to know what I am doing wrong here or how I can get the values from entireField in StartUp class to the FieldData fData in CharacterController using the none-MonoBehaviour class PlayField? I thought the this.singleField-array would have values, but not during the Method call from CharacterController?

Answer 1

Erkan, I think you're going to need to take a step back and rethink how you're approaching this. Here's why I say that:

   //edit: playField is not supposed hold value, just to get
   //access to a method in PlayField
   PlayField playField; 

... that's not how things work. If you've got a 'main' PlayField that holds all your values, and initialize another one ... any time you call functions on that second one, it'll use the values from the second one. In your case, you're trying to call the GetFieldData function, which will grab field data from the second instance of PlayField - not the one you're going for.

So Where Do You Go From Here?

First, you might want to brush up a bit on Object Oriented Programming concepts. I'm not trying to be condescending - but it'll be hard to continue on with your program if you don't have a decent grasp on them.

Second, consider the use of 'static'. Static says, "I only have one instance of this throughout my program". Take the following for example:

class Playfield
{ /* code */ }

class SomeAlreadyExistingMainClassInYourCode
{
  static Playfield globalFieldInstance = new Playfield();
  /* rest of the class */
}

... at this point, you've got a single Playfield that's accessible throughout your program: SomeAlreadyExistingMainClassInYourCode.globalFieldInstance.

You shouldn't overuse/abuse this - but if you're only intending on having a single instance of an object being created, creating a static instance of it is a good way to do.

Answer 2

@m.rogalski Yes I was trying to avoid using a static too that's how this started.

Have solved the nullreference error. Really didn't think I had to initialize everything when I just wanted to use it only to call a method* in another class and use another instance of the same class for Return.

public class CharacterController : MonoBehaviour
{
   //edit: playField is not supposed hold value, just to get
   //access to a method in PlayField
   PlayField playField; 

   FieldData fData;           

   void Start(){
       playField = new PlayField();
       InitArray(playField,30,30);
       fData = new FieldData();
   }
  void InitArray(PlayField playfield int x, int y){
       playfield.singleField = new SingleField[x,y];
       for (int j =0; j< y;.. {
            for (int i..  {
                playfield.singleField[x,y] = new SingleField();
                playfield.singleField[x,y].fieldData = new FieldData();
            }
       }
  }
   void Update(){
      //The return was not supposed to be a field in this instance of
      //PlayField, but come from the PlayField class itself as 
      //this.singleField[x,y] (a array in PlayField)
      fData = playField.GetFieldData(5,6); //We're just telling it go to that method 
   } 
}

public class PlayField
{
    public SingleField[,] singleField = new SingleField[30,30];//evrything initailized and so on in the rest of the class here ommited. ect.

    public FieldData GetFieldData(int x,int y){
         //Here was the catch. Return values form this Class
         // and not read from the instance created in CharacterController
         //was giving me a nullrefence while I was using only FieldData
         return this.singleField[x,y].fieldData;
    }
}

This is solved for me. On to the next question. Thanks