Attribute Macro relm4::component

#[component]

Macro that implements relm4::Component or relm4::SimpleComponent and generates the corresponding widgets struct.

Attributes

To create public struct use #[component(pub)] or #[component(visibility = pub)].

Example

use relm4::prelude::*;
use gtk::prelude::*;

#[derive(Default)]
struct App {
    counter: u8,
}

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

#[relm4_macros::component(pub)]
impl SimpleComponent for App {
    type Init = u8;
    type Input = Msg;
    type Output = ();

    view! {
        gtk::Window {
            set_title: Some("Simple app"),
            set_default_size: (300, 100),
            gtk::Box {
                set_orientation: gtk::Orientation::Vertical,
                set_margin_all: 5,
                set_spacing: 5,

                gtk::Button {
                    set_label: "Increment",
                    connect_clicked => Msg::Increment,
                },
                gtk::Button {
                    set_label: "Decrement",
                    connect_clicked[sender] => move |_| {
                        sender.input(Msg::Decrement);
                    },
                },
                gtk::Label {
                    set_margin_all: 5,
                    #[watch]
                    set_label: &format!("Counter: {}", model.counter),
                }
            },
        }
    }

    fn init(
        counter: Self::Init,
        root: &Self::Root,
        sender: ComponentSender<Self>,
    ) -> ComponentParts<Self> {
        let model = Self { counter };

        let widgets = view_output!();

        ComponentParts { model, widgets }
    }

    fn update(&mut self, msg: Msg, _sender: ComponentSender<Self>) {
        match msg {
            Msg::Increment => {
                self.counter = self.counter.wrapping_add(1);
            }
            Msg::Decrement => {
                self.counter = self.counter.wrapping_sub(1);
            }
        }
    }
}

Notes on pre_view

Using return in pre_view will cause a compiler warning. In general, you don’t want to use return in pre_view as it will cause all following update functionality to be skipped.

struct App {}

#[relm4_macros::component]
impl SimpleComponent for App {
      /* Code omitted */

      fn pre_view() {
          return;
      }
}