How to stop clones sharing listener?

Question

Unity 4.6, scripting the buttons... Iterate through a directory and create a button for each file... The value of f.Name in the AddListener bit should be set independently for each button. Instead every button has the value of the last f.Name to be processed (the last file alphabetically in the directory). Any ideas?

 foreach (FileInfo f in fileInfo) {
     Button btnCurrLvl = (Button) Instantiate(btnLvl);
 
     btnCurrLvl.GetComponentInChildren<Text>().text = f.Name.Remove(f.Name.Length-5);
 
     Debug.Log(f.Name); // f.Name is different every time
     btnCurrLvl.name = f.Name; // renaming the btns works
     btnCurrLvl.GetComponent<Button>().onClick.AddListener(() => LoadLocalLvl(f.Name)); // all the listeners on all created buttons are set to the last value of f.Name!?
 }

Answer 1

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Answer by Kiwasi · Nov 11, 2014 at 06:32 AM

Shameless self promotion: I've got a video tutorial here on this.

This is the nature of loops and variable scopes. To fix you simply need to declare a local scope variable.

 string tempName = f.Name;
 btnCurrLvl.GetComponent<Button>().onClick.AddListener(() => LoadLocalLvl(tempName));

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Kiwasi · Nov 11, 2014 at 06:35 AM 0

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The longer explanation runs something like this:

f is declared outside of the loop. So it lasts longer then the loop does. Each iteration f changes. Your listener only holds a reference to the memory location of f. So a f changes in memory so does the listener.

By contrast my tempName is declared inside the loop. So it only lasts until the closing } of the loop. This means a new memory location is used for tempName each iteration through the loop. When your listener is called later the memory is correct.

jasmyn · May 04, 2015 at 12:12 AM 0

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Reference vs value, really should have remembered that one... Thanks. :)

Upfront_Applications · Nov 20, 2015 at 12:02 AM 0

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Hi, I tried this solution and it didn't work for me :/;

 foreach (Items it in ItemsToGenerate)
         {
             GameObject go = new GameObject() ;
             go.transform.SetParent (GlobalState.appController.searchScene.transform);
             go.tag = "Item";
             go.name =  it.itemName;
             go.transform.SetAsFirstSibling();
             int i = 0;
             if (!listView)
             {
                 Image image = go.AddComponent(typeof (Image)) as Image;
                 image.rectTransform.sizeDelta = new Vector2 ((Screen.width / maxColumns) - Screen.width * 0.03f, (Screen.width / maxColumns) - Screen.width * 0.03f);
                 image.rectTransform.pivot = new Vector2 (0f, image.rectTransform.rect.max.y * 0.02f);
                 //image.overrideSprite = it.image;
                 float spacer = column * (Screen.width *0.02f);
 
                 Vector3 slotPosition = new Vector3((Screen.width *0.02f) +(spacer) + (image.rectTransform.sizeDelta.x * column),
                                                    Screen.height - (Screen.height * 0.15f) - (image.rectTransform.sizeDelta.y * row),
                                                    0);
                 image.rectTransform.position  = slotPosition;
                 image.sprite = it.image[0];
 
                 Button b = go.AddComponent (typeof(Button)) as Button;
                 Items item = it;
                 b.onClick.AddListener (() => ItemListener(it));
 
                 if (column + 1 > maxColumns -1)
                 {
                     column = 0;
                     row ++;
                 }
 
                 else
                 {
                     column ++;
                 }
             }
 
             else
             {
 
             }
             i++;
         }
     }
 
     void ItemListener(Items it)
     {
         currentItem = it;
         ToItem();
         //GlobalState.DownloadItem(it.bundleLink);
     }

How to stop clones sharing listener?

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