relm 0.10.1

Asynchronous, GTK+-based, GUI library, inspired by Elm, written in Rust

= Relm

Asynchronous, GTK+-based, GUI library, inspired by Elm, written in Rust.

This library is in alpha stage: it has not been thoroughly tested and its API may change at any time.

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== Requirements

Since relm is based on GTK+, you need this library on your system in order to use it.

See[this page] for information on how to install GTK+.

== Usage

First, add this to you Cargo.toml:


gtk = "^0.1.2" relm = "^0.10.0" relm-derive = "^0.10.0"

Next, add this to your crate:


extern crate gtk; #[macro_use] extern crate relm; #[macro_use] extern crate relm_derive;

use relm::{Relm, Widget};

Then, create your model:


struct Model { // … }

The model contains the data related to a Widget. It may be updated by the Widget::update function.

Create your message enum:


#[derive(Msg)] enum Msg { // … Quit, }

Messages are sent to Widget::update to indicate that an event happened. The model can be updated when an event is received.

Create a struct which represents a Widget which contains the GTK+ widgets (in this case, the main window of the application) and the model:


struct Win { // … model: Model, window: Window, }

To make this struct a relm Widget that can be shown by the library, implement the Update and Widget traits:


impl Update for Win { // Specify the model used for this widget. type Model = Model; // Specify the model parameter used to init the model. type ModelParam = (); // Specify the type of the messages sent to the update function. type Msg = Msg;

// Return the initial model.
fn model(_: &Relm<Self>, _: ()) -> Model {
    Model {

// The model may be updated when a message is received.
// Widgets may also be updated in this function.
// Futures and streams can be connected to send a message when a value is ready.
fn update(&mut self, event: Msg) {
    match event {
        Msg::SomeEvent => {
            let future = create_future();
            relm.connect_exec_ignore_err(future, SomeEvent);
        Msg::Quit => gtk::main_quit(),

// The next method is optional.
// Futures and streams can be connected when the `Widget` is created in the
// `subscriptions()` method.
// fn subscriptions(&mut self, relm: &Relm<Self>) {
//     let stream = Interval::new(Duration::from_secs(1));
//     relm.connect_exec_ignore_err(stream, Tick);
// }


impl Widget for Win { // Specify the type of the root widget. type Root = Window;

// Return the root widget.
fn root(&self) -> Self::Root {

// Create the widgets.
fn view(relm: &Relm<Self>, model: Self::Model) -> Self {
    // GTK+ widgets are used normally within a `Widget`.
    let window = Window::new(WindowType::Toplevel);

    // Connect the signal `delete_event` to send the `Quit` message.
    connect!(relm, window, connect_delete_event(_, _), return (Some(Msg::Quit), Inhibit(false)));
    // There is also a `connect!()` macro for GTK+ events that do not need a
    // value to be returned in the callback.


    Win {
        window: window,


Finally, show this Widget by calling Win::run():


fn main() { Win::run(()).unwrap(); }

=== #[widget] attribute

For the nightly users, a #[widget] attribute is provided to simplify the creation of a widget.

This attribute does the following:

  • Provide a view! macro to create the widget with a declarative syntax.
  • Automatically create the fn root(), type Msg, type Model, type ModelParam and type Root items.
  • Automatically insert the call to Widget::set_property() in the update() function when assigning to an attribute of the model.
  • Automatically create the Widget struct.
  • Both traits can be implemented at once.

To be able to use this attribute, you need to add the relm-attributes crate in your Cargo.toml:


relm-attributes = "^0.10.0"

and to add the following code:



extern crate relm_attributes;

use relm_attributes::widget;

Here is an example using this attribute:


#[widget] impl Widget for Win { fn model() -> Model { Model { counter: 0, } }

fn update(&mut self, event: Msg) {
    match event {
        // A call to self.label1.set_text() is automatically inserted by the
        // attribute every time the model.counter attribute is updated.
        Msg::Decrement => self.model.counter -= 1,
        Msg::Increment => self.model.counter += 1,
        Msg::Quit => gtk::main_quit(),

view! {
    gtk::Window {
        gtk::Box {
            orientation: Vertical,
            gtk::Button {
                // By default, an event with one paramater is assumed.
                clicked => Increment,
                // Hence, the previous line is equivalent to:
                // clicked(_) => Increment,
                label: "+",
            gtk::Label {
                // Bind the text property of this Label to the counter attribute
                // of the model.
                // Every time the counter attribute is updated, the text property
                // will be updated too.
                text: &self.model.counter.to_string(),
            gtk::Button {
                clicked => Decrement,
                label: "-",
        // Use a tuple when you want to both send a message and return a value to
        // the GTK+ callback.
        delete_event(_, _) => (Quit, Inhibit(false)),


NOTE: The struct Win is now automatically created by the attribute, as are the function root() and the types Model, ModelParam, Msg and Container. You can still provide the method and the types if needed, but you cannot create the struct.


It is possible to use this syntax from stable Rust.

To do so, you need to replace the following:

[source, rust]

#[widget] impl Widget for Win { }


[source, rust]

#[widget] relm_widget! { impl Widget for Win { } }


WARNING: The #[widget] makes the generated struct public: hence, the corresponding model and message types must be public too.


Your program might be slower when using this attribute because the code generation is simple. For instance, the following code [source,rust]

fn update(&mut self, event: Msg, model: &mut Model) { for _ in 0..100 { model.counter += 1; } }

will generate this function: [source,rust]

fn update(&mut self, event: Msg, model: &mut Model) { for _ in 0..100 { model.counter += 1; self.label1.set_text(&model.counter.to_string()); } }



Also, the set_property() calls are currently only inserted when assigning to an attribute of the model. For instance, the following code [source,rust]

fn update(&mut self, event: Msg, model: &mut Model) { model.text.push_str("Text"); }

will not work as expected.

Please use the following variation if needed. [source,rust]

fn update(&mut self, event: Msg, model: &mut Model) { model.text += "Text"; }


For more information about how you can use relm, you can take a look at the[examples].

== Projects using relm