Add listener to multiple buttons

Question

I have a menuController that creates a matrix of buttons which represent the levels. When a certain button is clicked, that level should be loaded. However, it doesn't matter which button I click, I always get level 25 returned... altough the highest possible level is only 20. I think this has something to do with the lambda expression that is set to every button over and over but I don't know how to fix this.

 public class MenuController : MonoBehaviour {
     
         public GameObject btnLevelPrefab;
         public GameObject levelContainer;
         public GameObject communicationManager;
     
         private GameObject[,] btnLevels;
     
         void Start () {
             btnLevels = new GameObject[4, 5];
     
             for(int i = 0; i < 5; i++)
             {
                 for(int j = 0; j < 4; j++)
                 {
                     btnLevels[j,i] = Instantiate(btnLevelPrefab, new Vector3(63 + j*90, 500 - i*90, 0), Quaternion.identity) as GameObject;
                     btnLevels[j,i].transform.SetParent(levelContainer.transform);
                     btnLevels[j,i].GetComponentInChildren<Text>().text = (j+1+i*4).ToString();
                     btnLevels[j,i].GetComponent<Button>().onClick.AddListener(() => { startLevel(j + 1 + i * 4); });
                 }
             }
         }
         
         private void startLevel(int level)
         {
             Debug.Log(level); // Returns 25 everytime???
             communicationManager.GetComponent<CommunicationManager>().setLevel(level);
             Application.LoadLevel(1);
         }
     }

Answer 1

SOLUTION!!

For some reason the AddListener can only be attached to every single button when I send the button as parameter instead of an integer that represents the level.

The new working code is now:

 for(int i = 0; i < 5; i++)
         {
             for(int j = 0; j < 4; j++)
             {
                 btnLevels[j,i] = Instantiate(btnLevelPrefab, new Vector3(63 + j*90, 500 - i*90, 0), Quaternion.identity) as GameObject;
                 btnLevels[j,i].transform.SetParent(levelContainer.transform);
                 btnLevels[j,i].GetComponentInChildren<Text>().text = (j+1+i*4).ToString();
                 Button btnTemp = btnLevels[j, i].GetComponent<Button>();
                 btnLevels[j, i].GetComponent<Button>().onClick.AddListener(() => { startLevel(btnTemp); });
 
             }
         }
     }
     
     private void startLevel(Button btnLevel)
     {
         Debug.Log(btnLevel.GetComponentInChildren<Text>().text);
         communicationManager.GetComponent<CommunicationManager>().setLevel(int.Parse(btnLevel.GetComponentInChildren<Text>().text));
         Application.LoadLevel(1);
     }

Answer 2

Answer by Thajocoth · May 25, 2016 at 05:14 PM

The issue was that adding the functionality that way doesn't preserve the state of the variables used inside it.

 int i = 5;
 AddListener(() => { function(i); });
 i++;

This will call function(6) when clicked, because i later became 6. The fact that i was 5 when the listener was set up is irrelevant.

I've been burned by this before as well. I wish there was a way to say "The current value of" instead of "Whatever the value will be of" when doing that.

 (j + 1 + i * 4)

may as well be

 (4 + 1 + 5 * 4)

Which is 25.

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Add listener to multiple buttons

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