(Solved) An arraylist error I couldn't* fix

Scripting
1

I have a list of grid classes which contains a list of __l__and classes .I get a object reference is set to null reference exception error when I try to add something to the land class. I can’t seem to figure out what could be the problem*.* Here is the map creator script :

//creating the grid
                    grid myGrid = new grid();
              
                    //creating the city block/grid
                    blockNumber = Random.Range(0, denseCityBlocks.Length);
                    GameObject myBlock = Instantiate(denseCityBlocks[blockNumber], myBlocks[blockId].transform.position, transform.rotation);
                                
              
                    //creating the elements in the city block
                    for (int i = 0; i < myBlock.GetComponent<cityBlock>().Lands.Length; i++)
                    {
                        land myLand = new land();

                        //saving the land to mygrid
                        myGrid.myLands.Add(myLand); //this is where I get error
// the file runs perfectly without this line
                    }
              
                    //saving the grid to game state manager
                    gameStateManager.GetComponent<gameState>().myGrids.Add(myGrid);

Here is the grid class:

[System.Serializable]
public class grid {

  public int blockNumber;
  public int blockRotation;
  public List<land> myLands;
}
;

and the land class

[System.Serializable]
public class land {
  public bool isEmpty;
  public bool isOwned;

  public GameObject building;
  public bool hasBuildingOnIt;

  public GameObject decoration;
  public bool hasDecorationOnIt;


}
;

Can someone help me figuring out the problem? Thanks :slight_smile:

PS: I edited out some lines of code to make it easier to look at from the mapcreator script. The code runs the same way without those lines. I could add them back if required.

2

Hard to say without the exact error message and line number. Do you know which object it says has a null reference?
I’m guessing its this line here:

  for (int i = 0; i < myBlock.GetComponent<cityBlock>().Lands.Length; i++)

I can’t see the script for cityBlock, but I assume Lands is some List or array. When you instantiate a new myBlock is the script allocating space for the Lands with the new keyword?

3

Yes.

4

Lands is a array of gameobject in the city block prefab. It contains nothing else. Used to set position.

5

Figured out the problem, the nested myGrid.myLands had to be declared for each grid even after the class. I don’t think I am expressing myself correctly. But my fix was: 1. Declare a temporary new list. After creating all elements of the list pass it to myGrid.myLands using > myGrid.myLands = new List(templist);

My first time working with nested lists. Didn’t know nested lists work this way. [Added the fix incase someone runs into same problem(unlikely)]

6

In your constructor method for grid. Add myLands = new List<Land>();
Then you wont need to assign it in a different class.

1 Like
7

Ah, that’s what I needed to do. Thanks, I appreciate it. :slight_smile: