{"slug":"jame581-event-bus","name":"event-bus","description":"Use when implementing decoupled communication between nodes — global EventBus autoload with typed signals","long_description":"---\nname: event-bus\ndescription: Use when implementing decoupled communication between nodes — global EventBus autoload with typed signals\n---\n\n# Event Bus in Godot 4.3+\n\nA global signal hub that lets unrelated nodes communicate without holding references to each other. All examples target Godot 4.3+ with no deprecated APIs.\n\n> **Related skills:** **component-system** for direct signal communication between components, **csharp-signals** for C#-specific signal patterns, **dependency-injection** for alternative decoupling approaches, **ability-system** for an EventBus usage example with ability events.\n\n---\n\n## 1. What is an Event Bus\n\nAn EventBus is a singleton autoload that acts as a central registry for signals. Instead of nodes connecting directly to each other, every node connects to (or emits on) the shared EventBus. This removes the need for one node to hold a reference to another.\n\n```\nWithout EventBus With EventBus\n────────────── ──────────────────────────\nNodeA ──signal──► NodeB NodeA ──emit──► EventBus ──signal──► NodeB\n ──signal──► NodeC\n ──signal──► NodeD\n```\n\n**Flow diagram**\n\n```\n┌─────────┐ emit(player_died) ┌───────────┐ player_died ┌──────────┐\n│ NodeA │ ────────────────────► │ EventBus │ ───────────────► │ NodeB │\n│(Player) │ │(Autoload) │ │ (UI) │\n└─────────┘ └───────────┘ ───────────────► └──────────┘\n player_died ┌──────────┐\n │ NodeC │\n │(AudioMgr)│\n └──────────┘\n```\n\nNodeA emits the signal. NodeB and NodeC each connected to EventBus independently. Neither knows the other exists.\n\n---\n\n## 2. When to Use vs Direct Signals\n\n| Scenario | Recommended approach |\n|--------------------------------------------|-------------------------------|\n| Parent notifying its own child | Direct signal or method call |\n| Child notifying its parent | Direct signal (bubble up) |\n| Two nodes with the same parent | Direct signal via parent |\n| Completely unrelated nodes in the tree | Event bus |\n| UI reacting to gameplay state changes | Event bus |\n| Audio manager reacting to game events | Event bus |\n| Data manager / save system reacting | Event bus |\n| Tight, performance-sensitive inner loop | Direct method call |\n\n**Rule of thumb:** if you would otherwise need `get_node(\"../../SomeDistantNode\")` or a hard-coded NodePath, the event bus is a better fit.\n\n---\n\n## 3. Basic EventBus\n\nCreate `res://autoloads/event_bus.gd` (or `EventBus.cs`), then register it in **Project → Project Settings → Autoload** with the name `EventBus`.\n\n### GDScript (`autoloads/event_bus.gd`)\n\n```gdscript\nextends Node\n\n## Emitted when the player character has died.\nsignal player_died\n\n## Emitted whenever the score changes.\nsignal score_changed(new_score: int)\n\n## Emitted when a level finishes successfully.\nsignal level_completed(level_id: int)\n\n## Emitted when the player picks up a collectible.\nsignal item_collected(item_name: String)\n\n## Emitted when the player's health changes.\nsignal health_changed(current: int, maximum: int)\n```\n\n### C# (`Autoloads/EventBus.cs`)\n\n```csharp\nusing Godot;\n\n/// \n/// Global signal hub. Register as an autoload named \"EventBus\".\n/// \npublic partial class EventBus : Node\n{\n /// Emitted when the player character has died.\n [Signal] public delegate void PlayerDiedEventHandler();\n\n /// Emitted whenever the score changes.\n [Signal] public delegate void ScoreChangedEventHandler(int newScore);\n\n /// Emitted when a level finishes successfully.\n [Signal] public delegate void LevelCompletedEventHandler(int levelId);\n\n /// Emitted when the player picks up a collectible.\n [Signal] public delegate void ItemCollectedEventHandler(string itemName);\n\n /// Emitted when the player's health changes.\n [Signal] public delegate void HealthChangedEventHandler(int current, int maximum);\n}\n```\n\n---\n\n## 4. Connecting to Events\n\nConsumers connect in `_ready()`. In C#, always disconnect in `_ExitTree()` to avoid dangling delegates and memory leaks.\n\n### GDScript\n\n```gdscript\nextends CanvasLayer\n\n# GDScript connections are reference-counted and cleaned up automatically\n# when the node is freed, but explicit disconnection is still good practice\n# for long-lived nodes that reconnect frequently.\n\nfunc _ready() -> void:\n EventBus.player_died.connect(_on_player_died)\n EventBus.score_changed.connect(_on_score_changed)\n EventBus.health_changed.connect(_on_health_changed)\n\n\nfunc _exit_tree() -> void:\n EventBus.player_died.disconnect(_on_player_died)\n EventBus.score_changed.disconnect(_on_score_changed)\n EventBus.health_changed.disconnect(_on_health_changed)\n\n\nfunc _on_player_died() -> void:\n $DeathScreen.show()\n\n\nfunc _on_score_changed(new_score: int) -> void:\n $ScoreLabel.text = \"Score: %d\" % new_score\n\n\nfunc _on_health_changed(current: int, maximum: int) -> void:\n $HealthBar.value = float(current) / float(maximum) * 100.0\n```\n\n### C#\n\n```csharp\nusing Godot;\n\npublic partial class HudLayer : CanvasLayer\n{\n private EventBus _eventBus;\n\n public override void _Ready()\n {\n _eventBus = GetNode(\"/root/EventBus\");\n\n // Connect using strongly-typed delegate handlers\n _eventBus.PlayerDied += OnPlayerDied;\n _eventBus.ScoreChanged += OnScoreChanged;\n _eventBus.HealthChanged += OnHealthChanged;\n }\n\n // IMPORTANT: Always disconnect in _ExitTree() in C#.\n // C# delegates are not automatically cleaned up when a node is freed.\n // Failing to disconnect causes the EventBus to hold a reference to the\n // freed node, leading to memory leaks and InvalidOperationExceptions.\n public override void _ExitTree()\n {\n _eventBus.PlayerDied -= OnPlayerDied;\n _eventBus.ScoreChanged -= OnScoreChanged;\n _eventBus.HealthChanged -= OnHealthChanged;\n }\n\n private void OnPlayerDied()\n {\n GetNode(\"DeathScreen\").Show();\n }\n\n private void OnScoreChanged(int newScore)\n {\n GetNode