ModernUO/dev-docs/events.md

ModernUO Event System

This document covers ModernUO's event system, including EventSink static events and the CodeGeneratedEvents system for custom entity events.

Overview

ModernUO provides two event mechanisms:

1. EventSink: Static events for core game lifecycle (login, logout, death, speech, etc.)
2. CodeGeneratedEvents: Attribute-based events on game entities (player login, creature death, etc.)

EventSink

Architecture

EventSink is a static partial class spread across multiple files in Projects/Server/Events/. Each event is defined as a public static event Action<T> with a corresponding InvokeXxx() method.

Subscribing to Events

Subscribe in your Configure() static method:

public static class MySystem
{
    public static void Configure()
    {
        EventSink.Connected += OnPlayerConnected;
        EventSink.Disconnected += OnPlayerDisconnected;
        EventSink.Speech += OnSpeech;
        EventSink.ServerStarted += OnServerStarted;
    }

    private static void OnPlayerConnected(Mobile m)
    {
        if (m is PlayerMobile pm)
            pm.SendMessage("Welcome to the server!");
    }

    private static void OnPlayerDisconnected(Mobile m)
    {
        // Cleanup player state
    }

    private static void OnSpeech(SpeechEventArgs e)
    {
        if (e.Speech.InsensitiveContains("help"))
        {
            e.Mobile.SendMessage("Type [help for commands.");
            e.Handled = true;
        }
    }

    private static void OnServerStarted()
    {
        // Initialize after all systems loaded
    }
}

Available Events

Server Lifecycle

Event	Signature	When
ServerStarted	Action	Server fully initialized
Shutdown	Action	Server shutting down
WorldLoad	Action	World loaded from saves
WorldSave	Action	World save triggered
WorldSavePostSnapshot	Action<WorldSavePostSnapshotEventArgs>	After save snapshot
ServerCrashed	Action<ServerCrashedEventArgs>	Unhandled exception

Player Connection

Event	Signature	When
Connected	Action<Mobile>	Player connected to server
BeforeDisconnected	Action<Mobile>	About to disconnect
Disconnected	Action<Mobile>	Player disconnected
Logout	Action<Mobile>	Player logged out

Account

Event	Signature	When
AccountLogin	Action<AccountLoginEventArgs>	Account login attempt

Communication

Event	Signature	When
Speech	Action<SpeechEventArgs>	Player speaks
PaperdollRequest	Action<Mobile, Mobile>	Paperdoll opened (beholder, beheld)

Combat

Event	Signature	When
AggressiveAction	Action<AggressiveActionEventArgs>	Aggressive action taken

Movement

Event	Signature	When
Movement	Action<MovementEventArgs>	Player moves

Network

Event	Signature	When
SocketConnect	Action<SocketConnectEventArgs>	New socket connection

EventArgs Classes

SpeechEventArgs

public class SpeechEventArgs
{
    public Mobile Mobile { get; }
    public string Speech { get; set; }     // Can modify speech text
    public MessageType Type { get; }
    public int Hue { get; }
    public int[] Keywords { get; }
    public bool Handled { get; set; }      // Set true to consume
    public bool Blocked { get; set; }      // Set true to block
    public bool HasKeyword(int keyword);
}

AccountLoginEventArgs

public class AccountLoginEventArgs
{
    public NetState State { get; }
    public string Username { get; }
    public string Password { get; }
    public bool Accepted { get; set; }           // Set false to reject
    public ALRReason RejectReason { get; set; }  // Reason for rejection
}

MovementEventArgs (Pooled)

public class MovementEventArgs
{
    public Mobile Mobile { get; }
    public Direction Direction { get; }
    public bool Blocked { get; set; }  // Set true to block movement

    // Object pooling
    public static MovementEventArgs Create(Mobile m, Direction dir);
    public void Free();  // Return to pool
}

AggressiveActionEventArgs (Pooled)

public class AggressiveActionEventArgs
{
    public Mobile Aggressed { get; }
    public Mobile Aggressor { get; }
    public bool Criminal { get; }

    public static AggressiveActionEventArgs Create(Mobile aggressed, Mobile aggressor, bool criminal);
    public void Free();
}

WorldSavePostSnapshotEventArgs

public class WorldSavePostSnapshotEventArgs
{
    public string OldSavePath { get; }
    public string NewSavePath { get; }
}

ServerCrashedEventArgs

public class ServerCrashedEventArgs
{
    public Exception Exception { get; }
    public bool Close { get; set; }  // Set false to continue running
}

SocketConnectEventArgs

public class SocketConnectEventArgs
{
    public IPAddress Address { get; }
    public bool AllowConnection { get; set; }  // Set false to reject
}

Creating Custom EventSink Events

Add to EventSink as a partial class:

// Projects/Server/Events/MyCustomEvent.cs
namespace Server;

public static partial class EventSink
{
    public static event Action<Mobile, Item> ItemCrafted;

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static void InvokeItemCrafted(Mobile crafter, Item item) =>
        ItemCrafted?.Invoke(crafter, item);
}

Then invoke from game code:

EventSink.InvokeItemCrafted(crafter, craftedItem);

---

CodeGeneratedEvents

For events on specific game entities, ModernUO uses source-generated events via the CodeGeneratedEvents package.

External reference: https://github.com/modernuo/CodeGeneratedEvents

Defining Generated Events

On the class that fires the event:

[GeneratedEvent(nameof(PlayerLoginEvent))]
public static partial void PlayerLoginEvent(PlayerMobile player);

Subscribing to Generated Events

On any class that handles the event:

[OnEvent(nameof(PlayerMobile.PlayerLoginEvent))]
public static void HandlePlayerLogin(PlayerMobile player)
{
    // Handle the event
}

Known Generated Events

• PlayerMobile.PlayerLoginEvent -- Player logs in
• PlayerMobile.PlayerDeathEvent -- Player dies
• BaseCreature.CreatureDeathEvent -- Creature dies

---

Static Content Events

Generated events dispatch statically inside UOContent; content that other assemblies must observe exposes a plain static event instead (shape: Projects/UOContent/Engines/Help/HelpEvents.cs).

• SkillEvents.SkillUsed -- Action<Mobile, Skill, bool success>, raised once per skill attempt from the four Mobile_SkillCheck* handlers with the attempt's outcome, including attempts resolved without a roll (too difficult, no challenge). Not raised when the mobile lacks the skill. Fires for every Mobile.

---

Event Args Pooling Pattern

Some EventArgs use object pooling to avoid allocation in hot paths:

// System that fires the event:
var args = MovementEventArgs.Create(mobile, direction);
EventSink.InvokeMovement(args);
// Check args.Blocked after invocation
args.Free();  // Return to pool

This pattern is used for high-frequency events (movement, combat) to minimize GC pressure.

---

Best Practices

1. Subscribe in Configure() -- called automatically during startup
2. Check player type -- Connected fires for all mobiles; cast to PlayerMobile if needed
3. Keep handlers fast -- they run on the game loop thread
4. Use Handled/Blocked -- on SpeechEventArgs to consume/block messages
5. Unsubscribe on disable -- if your system can be turned off, unsubscribe (-=) to prevent leaks
6. Don't throw exceptions -- unhandled exceptions in event handlers can crash the server

Key File References

File	Description
Projects/Server/Events/EventSink.cs	Core EventSink (partial)
Projects/Server/Events/SpeechEvent.cs	Speech event
Projects/Server/Events/MovementEvent.cs	Movement event (pooled)
Projects/Server/Events/AggressiveActionEvent.cs	Combat event (pooled)
Projects/Server/Events/AccountLoginEvent.cs	Account login
Projects/Server/Events/EventSink.cs	World save/load (WorldLoad, WorldSave, ServerStarted, Shutdown)
Projects/Server/Events/SocketConnectionEvent.cs	Socket connections
Projects/Server/Events/ServerCrashedEvent.cs	Crash handling