dotNet Events

Events

• Publishers fires of an event, all subscribers get notified that event was fired.
• Publisher is not aware of Subscribers.

EventHandler is simple Delegate.

public delegate void EventHandler(object sender, [EventAgrs](#eventargs) e )

It is dotNet standard. Not necessary to use. One may chose to define own custom delegate instead.

Delegate vs Events

A delegate is a type that defines a method signature. This allows you to pass methods as arguments to other methods. like a variable that holds a reference to a method, instead of a value.

An event, is essentially a special type of delegate that allows classes to communicate with each other in a loosely coupled way .

public event System.EventHandler OnKeyPress;

OnKeyPress(this, EventArgs.Empty); //Call it when needed

• Above code will throw error because there are no subscribers. Check for Null

OnKeyPress?.Invoke(this, EventArgs.Empty)

• In order to subscribe, we have to define a function that will recieve that event.
• Function signature needs to be same as event.

private void Fn_OnKeyPress(object sender, EventArgs e){}

• Finally, in order to subscribe, we use +=

OnKeyPress += Fn_OnKeyPress;

Do not forget to detach using -=

EventArgs

public event System.EventHandler<OnKeyPressEventArgs> OnKeyPress;

public class OnKeyPressEventArgs : EventArgs {
    public int keyNum;
}

OnKeyPress?.Invoke(this, new OnKeyPressEventArgs{keyNum=11});

private void Fn_OnKeyPress(object sender, OnKeyPressEventArgs e){}

Delegates

• Stores a function in a variable
• Delegates are essentially function signatures, without any implementation

public delegate void SimpleDelegate();

private SimpleDelegate simpleDelegateFunction;

private void MySimpleDelegateFunction() 
{ Debug.Log("Hello"); }

private void SecondSimpleDelegateFunction() 
{ Debug.Log("bye"); }

simpleDelegateFunction = MySimpleDelegateFunction;
simpleDelegateFunction();

simpleDelegateFunction = SecondSimpleDelegateFunction;
simpleDelegateFunction();

Multicasting

simpleDelegateFunction = MySimpleDelegateFunction;
simpleDelegateFunction += SecondSimpleDelegateFunction;
simpleDelegateFunction();

Predefined Delegates

1. Action
2. func
3. [de]

Delegates for PubSub

public delegate void OnKeyPressEventDelegate(int i);

Events with custom delegates

• instead of EventHandler delegate

public event OnKeyPressEventDelegate OnKeyPressEvent;

OnKeyPressEvent?.Invoke(11);

Action

Action is the default delegate. It retuns void. It has a generic version, which can be defined with different types.

//Action = delegate void System.Action()
pubic event Action OnKeyOne;

public event Action<bool> OnKeyTwo;

public event Action<int, float, bool> OnKeyThree;

OnKeyTwo?.Invoke(true);