Question How to use the userData attribute with events?

In our game we dynamically create a list of buttons depending on what options a player has. What I would like to do is something like this:

Code (CSharp):

1. foreach( var option in options) {
2.    var button = new Button();
3.    // ...
4.    // remember which option belongs to each button
5.    button.userData = option;
6.    button.clicked += OnButtonClicked;
7. }
8.  
9. // ...
10.  
11. private void OnButtonClicked() {
12.     // now i would like to have my option back
13.     // but at this time i only know that a button was
14.    // clicked, not which one. If this function would take
15.    // a parameter with the event or the clicked element I could
16.    // use it.
17. }

I could solve this by using a lambda function like this:

Code (CSharp):

1. foreach( var option in options) {
2.    var button = new Button();
3.    // ...
4.    button.clicked += () => {  // do something with the option here }
5. }

But then I cannot un-register the function from the

clicked

event anymore. Also what is the point of having a

userData

attribute if you cannot access it in events because you don't know which element fired the event. I seem to be missing something here. Could someone shed some light on how the

userData

property is supposed to be used together with events?

 

Button.clicked would be an Action<Button> rather than an Action, which would allow OnButtonClicked to take a Button argument.

You should probably also not name the class Button, since that's a built-in Unity thing! I got confused and tried to look for .userData in the Button API page before I saw that you were new()ing it.

 

@Baste you mean this is how the UI Elements API should be, right? Because right now it is just an

Action

, not an

Action<Button>

.

 

Oh whoops, forgot which subforum I was in.

So, yeah, disregard that.

 

You can use nested methods like so:

Code (CSharp):

1. foreach (var option in options)
2. {
3.     var button = new Button();
4.     button.clicked += OnButtonClicked;
5.     resetAllButtons += () => button.clicked -= OnButtonClicked;
6.  
7.     void OnButtonClicked()
8.     {
9.         Debug.Log($"Clicked on: {option}");
10.     }
11. }

or Action variable if you use .NET 3.5

Code (CSharp):

1. foreach (var option in options)
2. {
3.     var button = new Button();
4.     Action onButtonClicked = () =>
5.     {
6.         Debug.Log($"Clicked on: {option}");
7.     };
8.    
9.     button.clicked += onButtonClicked;
10.     resetAllButtons += () => button.clicked -= onButtonClicked;
11. }

You can also overwrite the on-click callback like this:

Code (csharp):

1. button.clickable = new Clickable(OnButtonClicked);

 

@ErnestSurys thank you, overwriting the clickable looks like the thing I need.

The thing with the

resetAllButtons

event handler seems to just shift the problem elsewhere, because you need to remove your nested function from that event somehow, or you will probably build a memory leak by this.

Still i think if one would have an

Action<Event> 

or

Action<Button>

as the

clicked

event signature one would need less code acrobatics.

That being said, I'll roll with the

clickable

approach for now. Thank you again @ErnestSurys .