Module glib::subclass

Module containing infrastructure for subclassing GObjects and registering boxed types.

Example for registering a glib::Object subclass

The following code implements a subclass of glib::Object with a string-typed “name” property.

use glib::prelude::*;
use glib::subclass;
use glib::subclass::prelude::*;
use glib::{Variant, VariantType};

use std::cell::{Cell, RefCell};

#[derive(Debug, Eq, PartialEq, Clone, Copy, glib::Enum)]
#[repr(u32)]
// type_name: GType name of the enum (mandatory)
#[enum_type(name = "SimpleObjectAnimal")]
enum Animal {
    Goat = 0,
    #[enum_value(name = "The Dog")]
    Dog = 1,
    // name: the name of the GEnumValue (optional), default to the enum name in CamelCase
    // nick: the nick of the GEnumValue (optional), default to the enum name in kebab-case
    #[enum_value(name = "The Cat", nick = "chat")]
    Cat = 2,
}

impl Default for Animal {
    fn default() -> Self {
        Animal::Goat
    }
}

#[glib::flags(name = "MyFlags")]
enum MyFlags {
    #[flags_value(name = "Flag A", nick = "nick-a")]
    A = 0b00000001,
    #[flags_value(name = "Flag B")]
    B = 0b00000010,
    #[flags_value(skip)]
    AB = Self::A.bits() | Self::B.bits(),
    C = 0b00000100,
}

impl Default for MyFlags {
    fn default() -> Self {
        MyFlags::A
    }
}

mod imp {
    use super::*;

    // This is the struct containing all state carried with
    // the new type. Generally this has to make use of
    // interior mutability.
    // If it implements the `Default` trait, then `Self::default()`
    // will be called every time a new instance is created.
    #[derive(Default)]
    pub struct SimpleObject {
        name: RefCell<Option<String>>,
        animal: Cell<Animal>,
        flags: Cell<MyFlags>,
        variant: RefCell<Option<Variant>>,
    }

    // ObjectSubclass is the trait that defines the new type and
    // contains all information needed by the GObject type system,
    // including the new type's name, parent type, etc.
    // If you do not want to implement `Default`, you can provide
    // a `new()` method.
    #[glib::object_subclass]
    impl ObjectSubclass for SimpleObject {
        // This type name must be unique per process.
        const NAME: &'static str = "SimpleObject";

        type Type = super::SimpleObject;

        // The parent type this one is inheriting from.
        // Optional, if not specified it defaults to `glib::Object`
        type ParentType = glib::Object;

        // Interfaces this type implements.
        // Optional, if not specified it defaults to `()`
        type Interfaces = ();
    }

    // Trait that is used to override virtual methods of glib::Object.
    impl ObjectImpl for SimpleObject {
        // Called once in the very beginning to list all properties of this class.
        fn properties() -> &'static [glib::ParamSpec] {
            use std::sync::OnceLock;
            static PROPERTIES: OnceLock<Vec<glib::ParamSpec>> = OnceLock::new();
            PROPERTIES.get_or_init(|| {
                vec![
                    glib::ParamSpecString::builder("name")
                        .build(),
                    glib::ParamSpecEnum::builder::<Animal>("animal")
                        .build(),
                    glib::ParamSpecFlags::builder::<MyFlags>("flags")
                        .build(),
                    glib::ParamSpecVariant::builder("variant", glib::VariantTy::ANY)
                        .build(),
                ]
            })
        }

        // Called whenever a property is set on this instance. The id
        // is the same as the index of the property in the PROPERTIES array.
        fn set_property(&self, _id: usize, value: &glib::Value, pspec: &glib::ParamSpec) {
            match pspec.name() {
                "name" => {
                    let name = value
                        .get()
                        .expect("type conformity checked by `Object::set_property`");
                    self.name.replace(name);
                },
                "animal" => {
                    let animal = value
                        .get()
                        .expect("type conformity checked by `Object::set_property`");
                    self.animal.replace(animal);
                },
                "flags" => {
                    let flags = value
                        .get()
                        .expect("type conformity checked by `Object::set_property`");
                    self.flags.replace(flags);
                },
                "variant" => {
                    let variant = value
                        .get()
                        .expect("type conformity checked by `Object::set_property`");
                    self.variant.replace(variant);
                },
                _ => unimplemented!(),
            }
        }

        // Called whenever a property is retrieved from this instance. The id
        // is the same as the index of the property in the PROPERTIES array.
        fn property(&self, _id: usize, pspec: &glib::ParamSpec) -> glib::Value {
            match pspec.name() {
                "name" => self.name.borrow().to_value(),
                "animal" => self.animal.get().to_value(),
                "flags" => self.flags.get().to_value(),
                "variant" => self.variant.borrow().to_value(),
                _ => unimplemented!(),
            }
        }

        // Called right after construction of the instance.
        fn constructed(&self) {
            // Chain up to the parent type's implementation of this virtual
            // method.
            self.parent_constructed();

            // And here we could do our own initialization.
        }
    }
}

// Optionally, define a wrapper type to make it more ergonomic to use from Rust
glib::wrapper! {
    pub struct SimpleObject(ObjectSubclass<imp::SimpleObject>);
}

impl SimpleObject {
    // Create an object instance of the new type.
    pub fn new() -> Self {
        glib::Object::new()
    }
}

pub fn main() {
    let obj = SimpleObject::new();

    // Get the name property and change its value.
    assert_eq!(obj.property::<Option<String>>("name"), None);
    obj.set_property("name", "test");
    assert_eq!(&obj.property::<String>("name"), "test");

    assert_eq!(obj.property::<Animal>("animal"), Animal::Goat);
    obj.set_property("animal", Animal::Cat);
    assert_eq!(obj.property::<Animal>("animal"), Animal::Cat);

    assert_eq!(obj.property::<MyFlags>("flags"), MyFlags::A);
    obj.set_property("flags", MyFlags::B);
    assert_eq!(obj.property::<MyFlags>("flags"), MyFlags::B);
}

Example for registering a glib::Object subclass within a module

The following code implements a subclass of glib::Object and registers it as a dynamic type.

use glib::prelude::*;
use glib::subclass::prelude::*;

pub mod imp {
    use super::*;

    // SimpleModuleObject is a dynamic type.
    #[derive(Default)]
    pub struct SimpleModuleObject;

    #[glib::object_subclass]
    #[object_subclass_dynamic]
    impl ObjectSubclass for SimpleModuleObject {
        const NAME: &'static str = "SimpleModuleObject";
        type Type = super::SimpleModuleObject;
    }

    impl ObjectImpl for SimpleModuleObject {}

    // SimpleTypeModule is the type module within the object subclass is registered as a dynamic type.
    #[derive(Default)]
    pub struct SimpleTypeModule;

    #[glib::object_subclass]
    impl ObjectSubclass for SimpleTypeModule {
        const NAME: &'static str = "SimpleTypeModule";
        type Type = super::SimpleTypeModule;
        type ParentType = glib::TypeModule;
        type Interfaces = (glib::TypePlugin,);
    }

    impl ObjectImpl for SimpleTypeModule {}

    impl TypeModuleImpl for SimpleTypeModule {
        /// Loads the module and registers the object subclass as a dynamic type.
        fn load(&self) -> bool {
            SimpleModuleObject::on_implementation_load(self.obj().upcast_ref::<glib::TypeModule>())
        }

        /// Unloads the module.
        fn unload(&self) {
            SimpleModuleObject::on_implementation_unload(self.obj().upcast_ref::<glib::TypeModule>());
        }
    }

    impl TypePluginImpl for SimpleTypeModule {}
}

// Optionally, defines a wrapper type to make SimpleModuleObject more ergonomic to use from Rust.
glib::wrapper! {
    pub struct SimpleModuleObject(ObjectSubclass<imp::SimpleModuleObject>);
}

// Optionally, defines a wrapper type to make SimpleTypeModule more ergonomic to use from Rust.
glib::wrapper! {
    pub struct SimpleTypeModule(ObjectSubclass<imp::SimpleTypeModule>)
    @extends glib::TypeModule, @implements glib::TypePlugin;
}

impl SimpleTypeModule {
    // Creates an object instance of the new type.
    pub fn new() -> Self {
        glib::Object::new()
    }
}

pub fn main() {
    let simple_type_module = SimpleTypeModule::new();
    // at this step, SimpleTypeModule has not been loaded therefore
    // SimpleModuleObject must not be registered yet.
    let simple_module_object_type = imp::SimpleModuleObject::type_();
    assert!(!simple_module_object_type.is_valid());

    // simulates the GLib type system to load the module.
    TypeModuleExt::use_(&simple_type_module);

    // at this step, SimpleModuleObject must have been registered.
    let simple_module_object_type = imp::SimpleModuleObject::type_();
    assert!(simple_module_object_type.is_valid());
}

Example for registering a glib::Object subclass within a plugin

The following code implements a subclass of glib::Object and registers it as a dynamic type.

use glib::prelude::*;
use glib::subclass::prelude::*;

pub mod imp {
    use super::*;

    // SimplePluginObject is a dynamic type.
    #[derive(Default)]
    pub struct SimplePluginObject;

    #[glib::object_subclass]
    #[object_subclass_dynamic(plugin_type = super::SimpleTypePlugin)]
    impl ObjectSubclass for SimplePluginObject {
        const NAME: &'static str = "SimplePluginObject";
        type Type = super::SimplePluginObject;
    }

    impl ObjectImpl for SimplePluginObject {}

    // SimpleTypePlugin is the type plugin within the object subclass is registered as a dynamic type.
    #[derive(Default)]
    pub struct SimpleTypePlugin {
        type_info: std::cell::Cell<Option<glib::TypeInfo>>
    }

    #[glib::object_subclass]
    impl ObjectSubclass for SimpleTypePlugin {
        const NAME: &'static str = "SimpleTypePlugin";
        type Type = super::SimpleTypePlugin;
        type Interfaces = (glib::TypePlugin,);
    }

    impl ObjectImpl for SimpleTypePlugin {}

    impl TypePluginImpl for SimpleTypePlugin {
        /// Uses the plugin and registers the object subclass as a dynamic type.
        fn use_plugin(&self) {
            SimplePluginObject::on_implementation_load(self.obj().as_ref());
        }

        /// Unuses the plugin.
        fn unuse_plugin(&self) {
            SimplePluginObject::on_implementation_unload(self.obj().as_ref());
        }

        /// Returns type information about the object subclass registered as a dynamic type.
        fn complete_type_info(&self, _type_: glib::Type) -> (glib::TypeInfo, glib::TypeValueTable) {
            assert!(self.type_info.get().is_some());
            // returns type info.
            (self.type_info.get().unwrap(), glib::TypeValueTable::default())
        }
    }

    impl TypePluginRegisterImpl for SimpleTypePlugin {
        fn register_dynamic_type(&self, parent_type: glib::Type, type_name: &str, type_info: &glib::TypeInfo, flags: glib::TypeFlags) -> glib::Type {
            let type_ = glib::Type::from_name(type_name).unwrap_or_else(|| {
                glib::Type::register_dynamic(parent_type, type_name, self.obj().upcast_ref::<glib::TypePlugin>(), flags)
            });
            if type_.is_valid() {
                // saves type info.
                self.type_info.set(Some(*type_info));
            }
            type_
        }
    }
}

// Optionally, defines a wrapper type to make SimplePluginObject more ergonomic to use from Rust.
glib::wrapper! {
    pub struct SimplePluginObject(ObjectSubclass<imp::SimplePluginObject>);
}

// Optionally, defines a wrapper type to make SimpleTypePlugin more ergonomic to use from Rust.
glib::wrapper! {
    pub struct SimpleTypePlugin(ObjectSubclass<imp::SimpleTypePlugin>)
    @implements glib::TypePlugin;
}

impl SimpleTypePlugin {
    // Creates an object instance of the new type.
    pub fn new() -> Self {
        glib::Object::new()
    }
}

pub fn main() {
    let simple_type_plugin = SimpleTypePlugin::new();
    // at this step, SimpleTypePlugin has not been used therefore
    // SimplePluginObject must not be registered yet.
    let simple_plugin_object_type = imp::SimplePluginObject::type_();
    assert!(!simple_plugin_object_type.is_valid());

    // simulates the GLib type system to use the plugin.
    TypePluginExt::use_(&simple_type_plugin);

    // at this step, SimplePluginObject must have been registered.
    let simple_plugin_object_type = imp::SimplePluginObject::type_();
    assert!(simple_plugin_object_type.is_valid());
}

//! # Example for registering a boxed type for a Rust struct

The following code boxed type for a tuple struct around String and uses it in combination with glib::Value.

use glib::prelude::*;
use glib::subclass;
use glib::subclass::prelude::*;

#[derive(Clone, Debug, PartialEq, Eq, glib::Boxed)]
#[boxed_type(name = "MyBoxed")]
struct MyBoxed(String);

pub fn main() {
    assert!(MyBoxed::static_type().is_valid());

    let b = MyBoxed(String::from("abc"));
    let v = b.to_value();
    let b2 = v.get::<&MyBoxed>().unwrap();
    assert_eq!(&b, b2);
}

Re-exports

• pub use self::boxed::register_boxed_type;
• pub use self::interface::register_dynamic_interface;
• pub use self::interface::register_interface;
• pub use self::signal::Signal;
• pub use self::signal::SignalClassHandlerToken;
• pub use self::signal::SignalId;
• pub use self::signal::SignalInvocationHint;
• pub use self::signal::SignalQuery;
• pub use self::signal::SignalType;
• pub use self::types::register_dynamic_type;
• pub use self::types::register_type;
• pub use self::types::InitializingObject;
• pub use self::types::InitializingType;
• pub use self::types::TypeData;

Modules

• basic
  This module contains basic instance and class structs to be used for GObject subclasses that don’t require any additional data in these structs and don’t provide any new virtual methods.
• boxed
  Module for registering boxed types for Rust types.
• interface
• object
  Module that contains all types needed for creating a direct subclass of GObject or implementing virtual methods of it.
• object_impl_ref 🔒
• prelude
  Prelude that re-exports all important traits from this crate.
• shared
  Module for registering shared types for Rust types.
• signal
• type_module
• type_plugin
• types
  Module that contains the basic infrastructure for subclassing GObject.

Structs

• ObjectImplRef
  Reference-counted wrapper around an ObjectSubclass reference.
• ObjectImplWeakRef
  Weak reference to an ObjectSubclass reference.