Clicking out and then in to the Unity Player while game is running will something throw me a Null Exception.

Hello,

happy new year to all of you!

I have this problem an the script background_beha. When I leave the Unity Player running while I check on my script in Mono Develop and click back to the player to continue playing, it sometimes throws me a Null Exception. After Debbuging it seems that "Grid" is null inside the Grid Class, while accessing the method NodeFromWorldPoint(). It is pretty weird and I don't have any clue on how to debug this.

When I play the game and don't switch windows or do any other stuff on the computer everything runs fine. The error only appears when I click in and out of the Unity Player Window.

As a background, the Grid Class:MonoBehaviour is a Component of the A* GameObject. In its Start() it Instantiate the Background Sprite (which has the background_beha Script attached) like this:

 void CreateBuild() {
         grid = new Node[gridSizeX, gridSizeY];
         worldBottomLeft = transform.position - Vector3.right * gridWorldSize.x / 2 - Vector3.up * gridWorldSize.y / 2;
 
         for (int x = 0; x < gridSizeX; x++) {
             for (int y = 0; y < gridSizeY; y++) {
                 Vector3 worldPoint = worldBottomLeft + Vector3.right * (x*nodeDiameter+nodeRadius) + Vector3.up *(y*nodeDiameter+nodeRadius);
                 Vector3 snapPoint = worldBottomLeft + Vector3.right * (x*nodeDiameter+nodeDiameter) + Vector3.up *(y*nodeDiameter+nodeDiameter);
 
                 grid [x, y] = new Node (worldPoint, true, x, y,snapPoint,primaryElement);
                 Instantiate (gridTexture.gameObject, grid[x,y].getWorldCoor (), Quaternion.Euler (Vector3.zero),gridParent);
                 Instantiate (backgroundSprite.gameObject, grid[x,y].getWorldCoor (), Quaternion.Euler (Vector3.zero),backgroundParent);
 
             }
         }
         gridParent.gameObject.SetActive (false);
     }

 

Here the NodeFromWorldPoint() inside the Grid Class:

     public Node NodeFromWorldPoint (Vector3 _worldPosition) {
         float percentX = (_worldPosition.x + gridWorldSize.x / 2) / gridWorldSize.x;
         float percentY = (_worldPosition.y + gridWorldSize.y / 2) / gridWorldSize.y;
         percentX = Mathf.Clamp01 (percentX);
         percentY = Mathf.Clamp01 (percentY);
 
         int x = Mathf.RoundToInt((gridSizeX - 1) * percentX);
         int y = Mathf.RoundToInt((gridSizeY - 1) * percentY);
 
         return grid [x, y];
     }
 

And here is the background_beha Class that is part of the backgroundSprite that is instantiated inside the Grid.

 public class background_beha : MonoBehaviour {
 
     public Sprite day,night;
     public GameObject ResText;
     public GameObject CoordText;
     public GameObject WeightPenaltyText;
 
     public GameObject elementIcon;
     public Vector3 localSlotLocation2;
     public Vector3 localSize = new Vector3 (0.4f, 0.4f, 1f);
 
     [SerializeField]
     private int showStatus = 0;
 
     private Grid theGrid;
     private Node currentNode;
     private Transform refObject;
     private float worldSizeX;
     private SpriteRenderer sr;
 
     private Inventory inventory;
 
     private List<GameObject> localSlot2 = new List<GameObject>();
 
     // Use this for initialization
     void Start () {
         ResText.SetActive (false);
         CoordText.SetActive (false);
         WeightPenaltyText.SetActive (false);
 
         Setting_Button_Controller.showRessourceCap += Setting_Button_Controller_showRessourceCap;
 
         refObject = GameObject.Find ("Night0.1Ref").transform;
         sr = GetComponent<SpriteRenderer> ();
 
         theGrid = GameObject.Find ("A*").GetComponent<Grid> ();
         currentNode = theGrid.NodeFromWorldPoint (transform.position);
         worldSizeX = theGrid.gridWorldSize.x;
         inventory = currentNode.inventory;
     }
 
 
 
     void Setting_Button_Controller_showRessourceCap ()
     {
         if (showStatus < 2)
             showStatus++;
         else
             showStatus = 0;
 
         switch (showStatus) {
         case 0:
             ResText.SetActive (false);
             CoordText.SetActive (false);
             WeightPenaltyText.SetActive (false);
             break;
         case 1:
             ResText.SetActive (true);
             CoordText.SetActive (true);
             WeightPenaltyText.SetActive (false);
             break;
         case 2:
             ResText.SetActive (false);
             CoordText.SetActive (true);
             WeightPenaltyText.SetActive (true);
             break;
         }
 
     }
     
     void Update() {
         float dif = Mathf.Abs (refObject.position.x - transform.position.x);
         float alpha = Mathf.Sin (dif * Mathf.PI / worldSizeX);
 
         if (currentNode == null) {
 // HERE THE ERROR APPEARS !! //
             Debug.LogError ("currentNode is null!");
             theGrid = GameObject.Find ("A*").GetComponent<Grid> ();
             currentNode = theGrid.NodeFromWorldPoint (transform.position);
         }
 
         if (alpha >= 0.5) {
             sr.sprite = day;    
             currentNode.isNight = false;
         } else {
             sr.sprite = night;
             currentNode.isNight = true;
         }
 
         ResText.GetComponent<TextMesh> ().text = currentNode.inventory.Count(currentNode.primaryElement).ToString();
         Vector2 gridPos = currentNode.getGridPosition ();
         CoordText.GetComponent<TextMesh> ().text = Mathf.RoundToInt (gridPos.x) + "," + Mathf.RoundToInt (gridPos.y);
         WeightPenaltyText.GetComponent<TextMesh> ().text = currentNode.movementPenalty.ToString ();
     }
 
     void ShowInv() {
         int counter = 0;
         foreach (Element _e in inventory.AllElementsinInventory()) {
             if (_e != currentNode.primaryElement) {
 
                 //print (gameObject.name+ ":found Element in Inventory: " + _e.elementName);
                 GameObject tempSlot = localSlot2.Find (i => i.name == "LocalSlot_" + _e.name);
                 if (tempSlot == null) {
                     tempSlot = (GameObject)Instantiate (elementIcon, transform);
                     tempSlot.transform.localScale = localSize;
                     tempSlot.transform.localPosition = localSlotLocation2 + new Vector3 (localSlotLocation2.x + 2 * counter, localSlotLocation2.y, localSlotLocation2.z);
                     tempSlot.name = "LocalSlot_" + _e.name;
                     tempSlot.GetComponent<ElementBehaivor> ().Element = _e;
                     tempSlot.GetComponent<ElementBehaivor> ().Amount = inventory.Count (_e);
 
                     localSlot2.Add (tempSlot);
                 } else {
                     if (inventory.Count (_e) > 0) {
                         tempSlot.SetActive (true);
                         tempSlot.transform.localPosition = localSlotLocation2 + new Vector3 (localSlotLocation2.x + 2 * counter, localSlotLocation2.y, localSlotLocation2.z);
                         tempSlot.GetComponent<ElementBehaivor> ().Amount = inventory.Count (_e);
                         counter++;
                     } else {
                         tempSlot.SetActive (false);
                     }
                 }
             }
         }
     }
 }

Project Background:

Prototyping Stage, A kind of city builder/strategy game. Doing it in my free time. First time developing a game. 10+ experience developing/designing/implementing business applications. I know the code is ugly.

Thanks for the help on guiding me where to keep digging into this.

Christian