Question Cannot Convert from 'System.Func<int>' to 'UnityEngine.Events.UnityAction'

Hello,
I'm not new to unity or C# but I've only recently started to try to try out more 'advanced' things like event systems and more complex design patterns after taking some courses on C++.
Right now I'm working on a very simple clicker game, and for an item system, I'm trying to add a listener to a button for a function pointer. The idea being that I can define the functionality somewhere else, however just trying to pass in the function pointer 'myEffect' into clickerButton.onClick.Addlistener yields the error in the title. I tried to google it but I couldn't find anything similar to my problem. So my question is, is there a way to convert from a function pointer to a Unity Action, or am I going about this all wrong?

Heres the code.
Basically i have an abstract Item class that contains the Effect struct, EffectType Enum, and some properties. TestItem inherits Item, defines Effects for _effects, and then AddItem, a function in PointManager, is supposed to loop through _effects and add a listener for each Effect.

Code (CSharp):

1.  public class TestItem : Item
2.     {
3.         int _cost = 100;
4.         int _count = 1;
5.         List<Effect> _effects = new List<Effect>();
6.  
7.         public override int Cost => _cost;
8.  
9.         public override int Count { get => _count; set => _count = value; }
10.  
11.         public override List<Effect> Effects => _effects;
12.    
13.         public TestItem()
14.         {
15.             Effect e1 = new Effect();
16.             e1.type = EffectType.click;
17.             e1.myEffect = ()=> PointManager.singleton.points += 1 * _count;
18.             _effects.Add(e1);
19.         }

Code (CSharp):

1.  
2.  public struct Effect
3.     {
4.        public  EffectType type;
5.        public Func<int> myEffect;
6.  
7.     }
8.  

Code (CSharp):

1.  
2.         public void AddItem(Item item)
3.         {
4.             int itemIndex = items.IndexOf(item);
5.             if (itemIndex > -1)
6.             {
7.                 ++items[itemIndex].Count;
8.             }
9.             else
10.             {
11.                 items.Add(item);
12.                 foreach(Effect e in item.Effects)
13.                 {
14.                     if(e.type == EffectType.click)
15.                     {
16.                         clickerButton.onClick.AddListener(e.myEffect);
17.                     }
18.                 }
19.                 itemIndex = items.Count - 1;
20.             }
21.  

Any help is greatly appreciated!

Edit: Was able to resolve this by changing they type of myEffect from Func<int> to UnityEngine.Events.UnityAction, which sounds obvious now that I've got it.

 

A UnityAction is a parameter-less delegate with no return type. Ergo, it supports methods with a signature of:

void SomeMethod()

.

Func<int>

is a delegate that supports methods that have a return type of the defined generic type. Ergo, methods with a signature of:

int GetSomeInt()

.

Naturally delegates with different signatures aren't compatible with one another.

 

What should that int parameter be?

If you don't care at all, you could do a little something like this:

Code (CSharp):

1. clickerButton.onClick.AddListener(() => e.myEffect(0));

...but I suspect that you want a meaningful value!

 

Oh Ok, thank you, That makes sense. What do you suggest I do instead? a Function pointer/func<> must have a non-void return type. I'm assuming some kind of delegate would be better but I haven't been able to wrap my head around them so far.

 

That is actually its return type, not a parameter.

 

Well buttons just to fire off events to say something has happened. It doesn't make sense for them to send values nor to expect a return type. Really, all you should be passing through to a button's

onClick.AddListener

call is a parameter-less method, rather than another delegate.

It kind of looks like

myEffect

(which should be capitalised as MyEffect) should just be an System.Action as I don't see you using the return of the

Func<int>

delegate.

Hard to say with the full context though. Hopefully you can use this information to find yourself the solution.

 

Func<T>

demands a return type, but

Action

doesn't!

Code (CSharp):

1. Action foo = () => print("Hello");
2. Action<int> bar = x => print(1 + x);
3. Func<int> baz = () => 1;
4. Func<int,int> buz = x => 1 + x;

In general, Func<T1,T2,T3> is a function that takes T1 and T2 and produces T3, and Action<T1,T2,T3> is a function that takes T1, T2, and T3, with no return type.

 

oh theres literally a thing called Action. Ok, ill see if i can just use that later tonight

Edit: oh so different problem, here a unity event cannot have a return type or any parameters. That said, that gave me the bright idea to just make myEffect into a UnityAction, which worked. Thanks for the help guys.

 

I actually dont need the return type, Its just there cause Func<> needs one. So if theres some other data type i could use that would be great.