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Signal

Встроенный тип, представляющий сигнал Object.

Описание

Signal is a built-in Variant type that represents a signal of an Object instance. Like all Variant types, it can be stored in variables and passed to functions. Signals allow all connected Callables (and by extension their respective objects) to listen and react to events, without directly referencing one another. This keeps the code flexible and easier to manage. You can check whether an Object has a given signal name using Object.has_signal().

In GDScript, signals can be declared with the signal keyword. In C#, you may use the [Signal] attribute on a delegate.

signal attacked

# Additional arguments may be declared.
# These arguments must be passed when the signal is emitted.
signal item_dropped(item_name, amount)

[Signal]
delegate void AttackedEventHandler();

// Additional arguments may be declared.
// These arguments must be passed when the signal is emitted.
[Signal]
delegate void ItemDroppedEventHandler(string itemName, int amount);

Connecting signals is one of the most common operations in Godot and the API gives many options to do so, which are described further down. The code block below shows the recommended approach.

func _ready():
    var button = Button.new()
    # `button_down` here is a Signal Variant type. We therefore call the Signal.connect() method, not Object.connect().
    # See discussion below for a more in-depth overview of the API.
    button.button_down.connect(_on_button_down)

    # This assumes that a `Player` class exists, which defines a `hit` signal.
    var player = Player.new()
    # We use Signal.connect() again, and we also use the Callable.bind() method,
    # which returns a new Callable with the parameter binds.
    player.hit.connect(_on_player_hit.bind("sword", 100))

func _on_button_down():
    print("Button down!")

func _on_player_hit(weapon_type, damage):
    print("Hit with weapon %s for %d damage." % [weapon_type, damage])

public override void _Ready()
{
    var button = new Button();
    // C# supports passing signals as events, so we can use this idiomatic construct:
    button.ButtonDown += OnButtonDown;

    // This assumes that a `Player` class exists, which defines a `Hit` signal.
    var player = new Player();
    // We can use lambdas when we need to bind additional parameters.
    player.Hit += () => OnPlayerHit("sword", 100);
}

private void OnButtonDown()
{
    GD.Print("Button down!");
}

private void OnPlayerHit(string weaponType, int damage)
{
    GD.Print($"Hit with weapon {weaponType} for {damage} damage.");
}

Object.connect() or Signal.connect()?

As seen above, the recommended method to connect signals is not Object.connect(). The code block below shows the four options for connecting signals, using either this legacy method or the recommended connect(), and using either an implicit Callable or a manually defined one.

func _ready():
    var button = Button.new()
    # Option 1: Object.connect() with an implicit Callable for the defined function.
    button.connect("button_down", _on_button_down)
    # Option 2: Object.connect() with a constructed Callable using a target object and method name.
    button.connect("button_down", Callable(self, "_on_button_down"))
    # Option 3: Signal.connect() with an implicit Callable for the defined function.
    button.button_down.connect(_on_button_down)
    # Option 4: Signal.connect() with a constructed Callable using a target object and method name.
    button.button_down.connect(Callable(self, "_on_button_down"))

func _on_button_down():
    print("Button down!")

public override void _Ready()
{
    var button = new Button();
    // Option 1: In C#, we can use signals as events and connect with this idiomatic syntax:
    button.ButtonDown += OnButtonDown;
    // Option 2: GodotObject.Connect() with a constructed Callable from a method group.
    button.Connect(Button.SignalName.ButtonDown, Callable.From(OnButtonDown));
    // Option 3: GodotObject.Connect() with a constructed Callable using a target object and method name.
    button.Connect(Button.SignalName.ButtonDown, new Callable(this, MethodName.OnButtonDown));
}

private void OnButtonDown()
{
    GD.Print("Button down!");
}

While all options have the same outcome (button's BaseButton.button_down signal will be connected to _on_button_down), option 3 offers the best validation: it will print a compile-time error if either the button_down Signal or the _on_button_down Callable are not defined. On the other hand, option 2 only relies on string names and will only be able to validate either names at runtime: it will generate an error at runtime if "button_down" is not a signal, or if "_on_button_down" is not a method in the object self. The main reason for using options 1, 2, or 4 would be if you actually need to use strings (e.g. to connect signals programmatically based on strings read from a configuration file). Otherwise, option 3 is the recommended (and fastest) method.

Binding and passing parameters:

The syntax to bind parameters is through Callable.bind(), which returns a copy of the Callable with its parameters bound.

When calling emit() or Object.emit_signal(), the signal parameters can be also passed. The examples below show the relationship between these signal parameters and bound parameters.

func _ready():
    # This assumes that a `Player` class exists, which defines a `hit` signal.
    var player = Player.new()
    # Using Callable.bind().
    player.hit.connect(_on_player_hit.bind("sword", 100))

    # Parameters added when emitting the signal are passed first.
    player.hit.emit("Dark lord", 5)

# We pass two arguments when emitting (`hit_by`, `level`),
# and bind two more arguments when connecting (`weapon_type`, `damage`).
func _on_player_hit(hit_by, level, weapon_type, damage):
    print("Hit by %s (level %d) with weapon %s for %d damage." % [hit_by, level, weapon_type, damage])

public override void _Ready()
{
    // This assumes that a `Player` class exists, which defines a `Hit` signal.
    var player = new Player();
    // Using lambda expressions that create a closure that captures the additional parameters.
    // The lambda only receives the parameters defined by the signal's delegate.
    player.Hit += (hitBy, level) => OnPlayerHit(hitBy, level, "sword", 100);

    // Parameters added when emitting the signal are passed first.
    player.EmitSignal(SignalName.Hit, "Dark lord", 5);
}

// We pass two arguments when emitting (`hit_by`, `level`),
// and bind two more arguments when connecting (`weapon_type`, `damage`).
private void OnPlayerHit(string hitBy, int level, string weaponType, int damage)
{
    GD.Print($"Hit by {hitBy} (level {level}) with weapon {weaponType} for {damage} damage.");
}

Note: In a boolean context, a signal will evaluate to false if it's null (see is_null()). Otherwise, a signal will always evaluate to true.

Примечание

Существуют заметные различия при использовании данного API с C#. Подробнее см. API различия C# и GDScript.

Обучающие материалы

Конструкторы

Signal	Signal()
Signal	Signal(from: Signal)
Signal	Signal(object: Object, signal: StringName)

Методы

int	connect(callable: Callable, flags: int = 0)
void	disconnect(callable: Callable)
void	emit(...) vararg const
Array	get_connections() const
StringName	get_name() const
Object	get_object() const
int	get_object_id() const
bool	has_connections() const
bool	is_connected(callable: Callable) const
bool	is_null() const

Операторы

bool	operator !=(right: Signal)
bool	operator ==(right: Signal)

Описания конструктора

Signal Signal() 🔗

Создает пустой Signal без привязанного имени объекта или сигнала.

Signal Signal(from: Signal)

Создает Signal как копию заданного Signal.

Signal Signal(object: Object, signal: StringName)

Создает объект Signal, ссылающийся на сигнал с именем signal в указанном object.

Описания метода

int connect(callable: Callable, flags: int = 0) 🔗

Соединяет этот сигнал с указанным callable. Дополнительно можно указать flags для настройки поведения соединения (см. константы ConnectFlags). Вы можете передать дополнительные аргументы в связанный callable, используя Callable.bind().

Сигнал может быть соединён с одним и тем же Callable только один раз. Если сигнал уже соединён, метод вернёт @GlobalScope.ERR_INVALID_PARAMETER и сгенерирует ошибку, за исключением случая, когда сигнал соединён с флагом Object.CONNECT_REFERENCE_COUNTED. Чтобы избежать этого, сначала используйте is_connected() для проверки существующих соединений.

for button in $Buttons.get_children():
    button.pressed.connect(_on_pressed.bind(button))

func _on_pressed(button):
    print(button.name, " was pressed")

Примечание: Если объект callable освобождён, соединение будет потеряно.

void disconnect(callable: Callable) 🔗

Отключает этот сигнал от указанного Callable. Если соединение не существует, генерирует ошибку. Используйте is_connected(), чтобы убедиться, что соединение существует.

void emit(...) vararg const 🔗

Выдает этот сигнал. Все Callable, подключенные к этому сигналу, будут активированы. Этот метод поддерживает переменное количество аргументов, поэтому параметры можно передавать в виде списка, разделенного запятыми.

Array get_connections() const 🔗

Возвращает Array соединений для этого сигнала. Каждое соединение представлено как Dictionary, который содержит три записи:

signal — ссылка на этот сигнал;
callable — ссылка на подключенный Callable;
flags — комбинация ConnectFlags.

StringName get_name() const 🔗

Возвращает имя этого сигнала.

Object get_object() const 🔗

Возвращает объект, испускающий этот сигнал.

int get_object_id() const 🔗

Возвращает идентификатор объекта, испускающего этот сигнал (см. Object.get_instance_id()).

bool has_connections() const 🔗

Возвращает true, если к этому сигналу подключен какой-либо Callable.

bool is_connected(callable: Callable) const 🔗

Возвращает true, если указанный Callable подключен к этому сигналу.

bool is_null() const 🔗

Возвращает true, если этот Signal не имеет объекта и имя сигнала пустое. Эквивалентно signal == Signal().

Описания оператора

bool operator !=(right: Signal) 🔗

Возвращает true, если сигналы не имеют одного и того же объекта и имени.

bool operator ==(right: Signal) 🔗

Возвращает true, если оба сигнала имеют один и тот же объект и имя.