SubEvent System

A lightweight, thread-safe pub/sub event system with conditional activation for .NET.

Subscribers can be paused and resumed at runtime without unsubscribing. Producers can auto-start/stop based on whether anyone is listening.

How It Works

var token = event.Subscribe(handler)    -> Token created (inactive by default)
token.IsActive = true                   -> Starts receiving events
token.IsActive = false                  -> Stops receiving (still subscribed)
event.Unsubscribe(token)                -> Token removed and disposed

Key Features

Feature	What it does
Activatable tokens	Toggle IsActive to pause/resume without resubscribing
Conditional activation	Provide a Func<bool> evaluated at each Invoke
Listener tracking	HasActiveListeners fires callbacks on first/last toggle
Thread-safe	Lock + snapshot pattern for concurrent invocation
Zero dependencies	Pure .NET

Quick Example

// Producer starts/stops based on listeners
var sensorEvent = new SubEvent<double>(
    OnFirstListenerActivation: () => sensor.StartStreaming(),
    OnLastListenerDeactivation: () => sensor.StopStreaming());

// Consumer subscribes
var token = sensorEvent.Subscribe(value => Console.WriteLine(value), initialState: true);

sensorEvent.Invoke(42.0);  // prints 42
token.IsActive = false;
sensorEvent.Invoke(99.0);  // nothing - token paused
token.IsActive = true;
sensorEvent.Invoke(7.0);   // prints 7

API

SubEvent

Method	Description
Subscribe(handler)	Subscribe inactive
Subscribe(handler, initialState)	Subscribe with explicit state
Subscribe(handler, activateCondition)	Subscribe with auto-eval condition
Unsubscribe(token)	Remove and dispose
Invoke(value)	Dispatch to active subscribers
Dispose()	Clean up all

SubEventToken

Member	Description
IsActive	Toggle activation
RefreshActivation()	Re-evaluate ShouldActivate
Dispose()	Null references for GC

Demo App (WPF)

A visual playground showing SubEvent in action:

• Producer generates Temperature/Pressure data every second
• Widgets subscribe via SubEvent<SensorReading>
• Checkboxes toggle token.IsActive in real-time
• Event log traces delivery
• LED indicators reflect HasActiveListeners

dotnet run --project SubEventSystem

Tests

dotnet test

Project Structure

SubEventSystem/
|-- Events/
|   |-- SubEvent.cs
|   |-- SubEventToken.cs
|-- MainWindow.xaml
|-- MainWindow.xaml.cs
|-- SensorReading.cs

SubEventSystemTests/
|-- SubEventTests.cs

Requirements

• .NET 8+
• Windows (WPF demo)

License

MIT