csharp-signals

Signals in C# (Godot 4.x)

This skill is C# only. For general C# conventions and project setup, see the csharp-godot skill. Godot signals in C# require a different mental model from GDScript: delegates declared with [Signal], strongly-typed +=/-= connections, and mandatory disconnection in _ExitTree(). All examples target Godot 4.x with no deprecated APIs.

Related skills: csharp-godot for C# conventions and project setup, event-bus for global signal hub architecture, component-system for signal-based component communication.

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1. Signal Declaration

Signals are declared as public delegate void with the [Signal] attribute inside a partial class that extends a Godot type. The delegate name must end with EventHandler — Godot strips that suffix to produce the signal name exposed to the engine.

using Godot;

public partial class Player : CharacterBody2D
{
    // Signal name in engine: "HealthChanged"
    [Signal] public delegate void HealthChangedEventHandler(int current, int maximum);

    // Signal name in engine: "Died"
    [Signal] public delegate void DiedEventHandler();

    // Signal name in engine: "ItemCollected"
    [Signal] public delegate void ItemCollectedEventHandler(string itemName);
}

Naming rules:

Delegate name	Engine signal name
HealthChangedEventHandler	HealthChanged
DiedEventHandler	Died
ItemCollectedEventHandler	ItemCollected
PlayerSpawnedEventHandler	PlayerSpawned

Omitting the EventHandler suffix compiles without error but registers no Godot signal — the signal will not appear in the editor and EmitSignal will throw at runtime.

Parameter type constraints: Signal parameters must be Godot-marshallable types: int, float, bool, string, Vector2, Vector3, Color, GodotObject subclasses, GodotDictionary, GodotArray. Plain C# classes, structs, and generics are not allowed as parameters.