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Clase Object

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Esta página describe la implementación en C++ de los objetos en Godot. ¿Buscas la referencia de la clase Object? Échale un vistazo aquí.

Definición General

Object is the base class for almost everything. Most classes in Godot inherit directly or indirectly from it. Declaring them is a matter of using a single macro like this:

class CustomObject : public Object {
    GDCLASS(CustomObject, Object); // This is required to inherit from Object.
};

Objects come with a lot of built-in functionality, like reflection and editable properties:

CustomObject *obj = memnew(CustomObject);
print_line("Object class: ", obj->get_class()); // print object class

OtherClass *obj2 = Object::cast_to<OtherClass>(obj); // Converting between classes, similar to dynamic_cast

Referencias:

• core/object/object.h

Registering Object classes

Most Object subclasses are registered by calling GDREGISTER_CLASS.

GDREGISTER_CLASS(MyCustomClass)

This will register it as a named, public class in the ClassDB, which will allow the class to be instantiated by scripts, code, or by deserialization. Note that classes registered as GDREGISTER_CLASS should expect to be instantiated or freed automatically, for example by the editor or the documentation system.

Besides GDREGISTER_CLASS, there are a few other modes of privateness:

// Registers the class publicly, but prevents automatic instantiation through ClassDB.
GDREGISTER_VIRTUAL_CLASS(MyCustomClass);

// Registers the class publicly, but prevents all instantiation through ClassDB.
GDREGISTER_ABSTRACT_CLASS(MyCustomClass);

// Registers the class in ClassDB, but marks it as private,
// such that it is not visible to scripts or extensions.
// This is the same as not registering the class explicitly at all
// - in this case, the class is registered as internal automatically
// when it is first constructed.
GDREGISTER_INTERNAL_CLASS(MyCustomClass);

// Registers the class such that it is only available at runtime (but not in the editor).
GDREGISTER_RUNTIME_CLASS(MyCustomClass);

It is also possible to use GDSOFTCLASS(MyCustomClass, SuperClass) instead of GDCLASS(MyCustomClass, SuperClass). Classes defined this way are not registered in the ClassDB at all. This is sometimes used for platform-specific subclasses.

Registering bindings

Object-derived classes can override the static function static void _bind_methods(). When the class is registered, this static function is called to register all the object methods, properties, constants, etc. It's only called once.

Dentro de _bind_methods, hay algunas cosas que se pueden hacer. Una de ellas es registrar funciones:

ClassDB::bind_method(D_METHOD("methodname", "arg1name", "arg2name", "arg3name"), &MyCustomType::method);

Default values for arguments can be passed as parameters at the end:

ClassDB::bind_method(D_METHOD("methodname", "arg1name", "arg2name", "arg3name"), &MyCustomType::method, DEFVAL(-1), DEFVAL(-2)); // Default values for arg2name (-1) and arg3name (-2).

Default values must be provided in the same order as they are declared, skipping required arguments and then providing default values for the optional ones. This matches the syntax for declaring methods in C++.

D_METHOD es una macro que convierte "methodname" en un StringName para mejorar la eficiencia. Los nombres de los argumentos se utilizan para la introspección, pero al compilar en modo de lanzamiento, la macro los ignora, por lo que las strings no se utilizan y se optimizan para que desaparezcan.

Puedes revisar el método _bind_methods de las clases Control u Object para ver más ejemplos.

Si solo estás agregando módulos y funcionalidades que no se espera que estén documentadas en detalle, el macro D_METHOD() puede ser ignorado de forma segura y simplemente puedes pasar un string con el nombre del método para mayor concisión.

Referencias:

• core/object/class_db.h

Constantes

Las clases a menudo tienen enumeraciones como esta:

enum SomeMode {
   MODE_FIRST,
   MODE_SECOND
};

For these to work when binding to methods, the enum must be declared convertible to int. A macro is provided to help with this:

VARIANT_ENUM_CAST(MyClass::SomeMode); // now functions that take SomeMode can be bound.

Las constantes también se pueden vincular dentro de _bind_methods, usando:

BIND_CONSTANT(MODE_FIRST);
BIND_CONSTANT(MODE_SECOND);

Propiedades (set/get)

Los objetos exportan propiedades, las propiedades son útiles para lo siguiente:

• Serializar y deserializar el objeto.

• Crear una lista de valores editables para la clase derivada de Object.

Properties are usually defined by the PropertyInfo() class and constructed as:

PropertyInfo(type, name, hint, hint_string, usage_flags)

Por ejemplo:

PropertyInfo(Variant::INT, "amount", PROPERTY_HINT_RANGE, "0,49,1", PROPERTY_USAGE_EDITOR)

This is an integer property named "amount". The hint is a range, and the range goes from 0 to 49 in steps of 1 (integers). It is only usable for the editor (editing the value visually) but won't be serialized.

Otro ejemplo:

PropertyInfo(Variant::STRING, "modes", PROPERTY_HINT_ENUM, "Enabled,Disabled,Turbo")

Esta es una propiedad de string, puede tomar cualquier string pero el editor sólo permitirá los que estén definidos como hint. Puesto que no se especificó ningún indicador de uso, los valores por defecto son PROPERTY_USAGE_STORAGE y PROPERTY_USAGE_EDITOR.

Hay muchas sugerencias (hints) y banderas de uso disponibles en "object.h", dales una revisión.

Las propiedades también pueden funcionar como propiedades de C# y accederse desde un script utilizando el indexado, pero este uso generalmente no se recomienda, ya que se prefiere usar funciones para mejorar la legibilidad. Muchas propiedades también están vinculadas con categorías, como por ejemplo "animation/frame", lo que también hace que el indexado sea imposible a menos que se utilice el operador [].

Desde _bind_methods(), las propiedades pueden ser creadas y enlazadas siempre y cuando existan funciones de configuración y obtención (set/get). Ejemplo:

ADD_PROPERTY(PropertyInfo(Variant::INT, "amount"), "set_amount", "get_amount")

Esto crea la propiedad utilizando el setter y el getter.

La vinculación de propiedades utilizando _set/_get/_get_property_list

Existe un método adicional para crear propiedades cuando se desea más flexibilidad (por ejemplo, agregar o eliminar propiedades en un contexto).

Las siguientes funciones pueden ser sobreescritas en una clase derivada de Object, NO las hagas virtuales, son llamadas para cada sobreescritura y las versiones anteriores no se invalidan (llamada multinivel).

protected:
     void _get_property_list(List<PropertyInfo> *r_props) const;      // return list of properties
     bool _get(const StringName &p_property, Variant &r_value) const; // return true if property was found
     bool _set(const StringName &p_property, const Variant &p_value); // return true if property was found

Esto también es un poco menos eficiente ya que p_property debe ser comparado con los nombres deseados en orden serial.

Señales

Objects can have a set of signals defined (similar to Delegates in other languages). This example shows how to connect to them:

// This is the function signature:
//
// Error connect(const StringName &p_signal, const Callable &p_callable, uint32_t p_flags = 0)
//
// For example:
obj->connect("signal_name_here", callable_mp(this, &MyCustomType::method), CONNECT_DEFERRED);

callable_mp is a macro to create a custom callable function pointer to member functions. For the values of p_flags, see ConnectFlags.

Agregar señales a una clase se hace en _bind_methods, utilizando el macro ADD_SIGNAL, por ejemplo:

ADD_SIGNAL(MethodInfo("been_killed"))

Object ownership and casting

Objects are allocated on the heap. There are two different ownership models:

• Objects derived from RefCounted are reference counted.

• All other objects are manually memory managed.

The ownership models are fundamentally different. Refer to the section for each respectively to learn how to create, store, and free the object.

When you do not know whether an object passed to you (via Object *) is RefCounted, and you need to store it, you should store its ObjectID rather than a pointer (as explained below, in the manual memory management section).

When an object is passed to you via Variant, especially when using deferred callbacks, it is possible that the contained Object * was already freed by the time your function runs. Instead of converting directly to Object *, you should use get_validated_object:

void do_something(Variant p_variant) {
    Object *object = p_variant.get_validated_object();
    ERR_FAIL_NULL(object);
}

Manual memory management

Manually memory managed objects are created using memnew and freed using memdelete:

Node *node = memnew(Node);
// ...
memdelete(node);
node = nullptr;

When you are not the sole owner of an object, storing a pointer to it is dangerous: The object may at any point be freed through other references to it, causing your pointer to become a dangling pointer, which will eventually result in a crash.

When storing objects you are not the only owner of, you should store its ObjectID rather than a pointer:

Node *node = memnew(Node);
ObjectID node_id = node.get_instance_id();
// ...
Object *maybe_node = ObjectDB::get_instance(node_id);
ERR_FAIL_NULL(maybe_node); // The node may have been freed between calls.

RefCounted memory management

RefCounted subclasses are memory managed with reference counting semantics.

They are constructed using memnew, and should be stored in Ref instances. When the last Ref instance is dropped, the object automatically self-destructs.

class MyRefCounted: public RefCounted {
    GDCLASS(MyReference, RefCounted);
};

Ref<MyRefCounted> my_ref = memnew(MyRefCounted);
// ...
// Ref holds shared ownership over the object, so the object
// will not be freed. As long as you have a valid, non-null
// Ref, it can be safely assumed the object is still valid.
my_ref->get_class_name();

You should never call memdelete for RefCounted subclasses, because there may be other owners of it.

You should also never store RefCounted subclasses using raw pointers, for example RefCounted *object = memnew(RefCounted). This is unsafe because other owners may destruct the object, leaving you with a dangling pointer, which will eventually result in a crash.

Referencias:

• core/object/ref_counted.h

Casteo dinámico

Godot proporciona el casteo dinámico entre clases derivadas de Object, por ejemplo:

void some_func(Object *p_object) {
     Button *button = Object::cast_to<Button>(p_object);
}

If the cast fails, nullptr is returned. This works the same as dynamic_cast, but does not use C++ RTTI.

Notificaciones

All objects in Godot have a _notification method that allows them to respond to engine-level callbacks that may relate to it. More information can be found on the Notificaciones en Godot page.

Recursos

Resource inherits from RefCounted, so all resources are reference counted. Resources can optionally contain a path, which reference a file on disk. This can be set with resource.set_path(path), though this is normally done by the resource loader. No two different resources can have the same path; attempting to do so will result in an error.

Los recursos sin una ruta también son aceptables.

Referencias:

• core/io/resource.h

Cargar un recurso

Los recursos se pueden cargar con la API ResourceLoader, de esta manera:

Ref<Resource> res = ResourceLoader::load("res://someresource.res")

If a reference to that resource has been loaded previously and is in memory, the ResourceLoader will return that reference. This means that there can be only one resource loaded from a file referenced on disk at the same time.

Referencias:

• core/io/resource_loader.h

Guardar un recurso

Guardar un recurso se puede hacer utilizando la API del salvador de recursos:

ResourceSaver::save("res://someresource.res", instance)

The instance will be saved, and sub resources that have a path to a file will be saved as a reference to that resource. Sub resources without a path will be bundled with the saved resource and assigned sub-IDs, like res://someresource.res::1. This also helps to cache them when loaded.

Referencias:

• core/io/resource_saver.h