Question How to pass arguments to callback functions using IPointerClickHandler

Since I don't want to use the Unity genuine Button component, I'm using an alternative class for Button that I created with reference to someone else's source.

Code (CSharp):

1. public class CustomButton:Monobehaiviour,IPointerClickHandler{
2.     public System.Action onClickCallback;
3.     public void OnPointerClick(PointerEventData eventData)
4.     {
5.         onClickCallback?.Invoke();
6.     }
7. }

However, I noticed a problem when using it in combination with List.

Code (CSharp):

1. private int BUTTON_NUM = 3;
2. void Start()
3. {
4.     for (int i = 0; i < BUTTON_NUM; i++)
5.     {
6.         roomButtons[i].onClickCallback = () => {
7.             OnClickRoomBtn(i);
8.         };
9.     }
10. }
11.  
12. private void OnClickRoomBtn(int roomNo)
13. {
14.     Debug.Log("RoomNo: "+ roomNo);
15. }
16.  

Click roomButtons[0] to
> RoomNo: 3

As mentioned above, I noticed that I can't pass the arguments as intended in the For syntax.

Code (CSharp):

1. void Start()
2. {  
3.     roomButtons[0].onClickCallback = () => {
4.         OnClickRoomBtn(0);
5.     };
6.     roomButtons[1].onClickCallback = () => {
7.         OnClickRoomBtn(1);
8.     };
9.     roomButtons[2].onClickCallback = () => {
10.         OnClickRoomBtn(2);
11.     };
12. }

Click roomButtons[0] to
> RoomNo: 0

In this way, if you write only the number of buttons, it will work, but I want to use the For statement.
Please let me know how I can modify this format to make it more convenient.

 

Simply put, you'd have to introduce your own delegate with parameters. Such as

System.Action<int>

.

 

Code (CSharp):

1.     for (int i = 0; i < BUTTON_NUM; i++)
2.     {
3.         roomButtons[i].onClickCallback = () => {
4.             OnClickRoomBtn(i);
5.         };
6.     }

That will capture reference to i not the value of i. So all the callbacks you create refer to the same i variable. This may be slightly surprising since in rest of C# it's almost impossible to make a reference to value type variables, and parts that allow you to make something similar require to be somewhat explicit about it.

So you need to do it this way:

Code (CSharp):

1.     for (int i = 0; i < BUTTON_NUM; i++)
2.     {
3.         int buttonNum = i;
4.         roomButtons[i].onClickCallback = () => {
5.             OnClickRoomBtn(buttonNum);
6.         };
7.     }

 

I just realized that I don't understand delegates very well. I will take this opportunity to study. Thank you very much.

 

Thank you, I was surprised how easy it was to solve.
It was necessary to repeat, including the definition of variables.