FuncEvent.md

FuncEvent

Namespace: SpawnDev.SpawnJS
Inheritance: CallbackEvent -> FuncEvent<TResult> -> FuncEvent<T1, TResult> -> ... -> FuncEvent<T1...T7, TResult>
Source: SpawnDev.SpawnJS/Events/FuncEvent.cs

FuncEvent works exactly like ActionEvent but wraps Func delegates instead of Action delegates, allowing a return value to be sent back to JavaScript. This is used for events where the JavaScript caller expects a return value from the handler - for example, the beforeunload event where returning a string shows a confirmation dialog.

Variants

Class	Description
FuncEvent<TResult>	No-argument event handler that returns TResult.
FuncEvent<T1, TResult>	Event handler with 1 argument that returns TResult.
FuncEvent<T1, T2, TResult>	Event handler with 2 arguments that returns TResult.
FuncEvent<T1, T2, T3, TResult>	Event handler with 3 arguments that returns TResult.
FuncEvent<T1, T2, T3, T4, TResult>	Event handler with 4 arguments that returns TResult.
FuncEvent<T1, T2, T3, T4, T5, TResult>	Event handler with 5 arguments that returns TResult.
FuncEvent<T1, T2, T3, T4, T5, T6, TResult>	Event handler with 6 arguments that returns TResult.
FuncEvent<T1, T2, T3, T4, T5, T6, T7, TResult>	Event handler with 7 arguments that returns TResult.

Constructors

// Using event name with addEventListener/removeEventListener delegates
new FuncEvent<TResult>(string eventName, Action<string, Callback> on, Action<string, Callback>? off)

// Using direct on/off delegates
new FuncEvent<TResult>(Action<Callback> on, Action<Callback>? off)

Operators

Operator	Description
+= Func	Subscribe a .NET Func delegate. Auto-creates and ref-counts the Callback.
-= Func	Unsubscribe a .NET Func delegate. Decrements ref count and removes the listener.
+= Callback	Subscribe a raw Callback instance.
-= Callback	Unsubscribe a raw Callback instance.

Methods

Method	Return Type	Description
On(Func<TResult> listener)	void	Add a listener that returns a value.
Off(Func<TResult> listener)	void	Remove a listener.
On(Func<T1, TResult> listener)	void	Add a typed listener (on FuncEvent<T1, TResult>).
Off(Func<T1, TResult> listener)	void	Remove a typed listener.

Example

// FuncEvent property on a SpawnJSObject wrapper
public FuncEvent<Event, string> OnBeforeUnload
{
    get => new FuncEvent<Event, string>("beforeunload", AddEventListener, RemoveEventListener);
    set { }
}

// Usage
string HandleBeforeUnload(Event e)
{
    return "Are you sure you want to leave?";
}

window.OnBeforeUnload += HandleBeforeUnload;
// ...
window.OnBeforeUnload -= HandleBeforeUnload;

Important Notes

• Same lifecycle rules as ActionEvent: every += must have a matching -= before disposal.
• The return value from the Func delegate is marshaled back to JavaScript as the event handler's return value.
• FuncEvent inherits from CallbackEvent just like ActionEvent - the only difference is Func vs Action delegate types.