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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 your Cargo.toml:

gtk = "^0.8.0"
relm = "^0.19.0"
relm-derive = "^0.19.0"

Next, add this to your crate:

use relm::{Relm, Update, Widget};
use gtk::prelude::*;
use gtk::{Window, Inhibit, WindowType};
use relm_derive::Msg;

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.
    fn update(&mut self, event: Msg) {
        match event {
            Msg::Quit => gtk::main_quit(),
        }
    }
}

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

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

    // 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.

        window.show_all();

        Win {
            model,
            window,
        }
    }
}

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

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

#[widget] attribute

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.

  • Update and Widget traits can be implemented at once.

To use this attribute, add the following code:

use relm_derive::widget;

Here is an example using this attribute:

#[derive(Msg)]
pub enum Msg {
    Decrement,
    Increment,
    Quit,
}

pub struct Model {
    counter: u32,
}

#[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 => Msg::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 => Msg::Decrement,
                    label: "-",
                },
            },
            // Use a tuple when you want to both send a message and return a value to
            // the GTK+ callback.
            delete_event(_, _) => (Msg::Quit, Inhibit(false)),
        }
    }
}
Note
The struct Win is now automatically created by the attribute, as are the function root() and the associated types Model, ModelParam, Msg and Container. You can still provide the method and the associated types if needed, but you cannot create the struct.
Warning
The #[widget] makes the generated struct public: hence, the corresponding model and message types must be public too.
Warning

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

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

will generate this function:

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

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

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

will not work as expected.

Please use the following variation if needed.

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

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

Donations

If you appreciate this project and want new features to be implemented, please support me on Patreon.

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

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