updating_widgets_from_outside.md

Updating Widgets From Outside

Consider that our widget has an internal state:

struct MyWidget {
    highlight: bool,
}

We use the highlight variable to change the color of our widget in the draw method.

fn draw(
    &self,
    _state: &Tree,
    renderer: &mut Renderer,
    _theme: &Theme,
    _style: &renderer::Style,
    layout: Layout<'_>,
    _cursor: mouse::Cursor,
    _viewport: &Rectangle,
) {
    renderer.fill_quad(
        Quad {
            bounds: layout.bounds(),
            border: Border {
                color: Color::from_rgb(0.6, 0.8, 1.0),
                width: 1.0,
                radius: 10.0.into(),
            },
            shadow: Shadow::default(),
        },
        if self.highlight {
            Color::from_rgb(0.6, 0.8, 1.0)
        } else {
            Color::from_rgb(0.0, 0.2, 0.4)
        },
    );
}

We would like to control the highlight variable from our app.

To do so, we make MyWidget to accept the highlight variable when the widget is constructed.

impl MyWidget {
    fn new(highlight: bool) -> Self {
        Self { highlight }
    }
}

Then, we initialize MyWidget in the view method of our app with an input value for the highlight variable.

struct MyApp {
    highlight: bool,
}

fn view(&self) -> iced::Element<'_, Message> {
    container(
        column![
            MyWidget::new(self.highlight),
        ]
    )
}

In this example, we control the highlight variable with a checkbox.

The full code is as follows:

use iced::{
    Border, Color, Element, Length, Rectangle, Shadow, Size, Task, Theme,
    advanced::{
        Layout, Widget, layout, mouse,
        renderer::{self, Quad},
        widget::Tree,
    },
    widget::{checkbox, column, container},
};

fn main() -> iced::Result {
    iced::application("My App", MyApp::update, MyApp::view).run_with(MyApp::new)
}

#[derive(Debug, Clone)]
enum Message {
    Highlight(bool),
}

#[derive(Default)]
struct MyApp {
    highlight: bool,
}

impl MyApp {
    fn new() -> (Self, Task<Message>) {
        (Self { highlight: false }, Task::none())
    }

    fn update(&mut self, message: Message) {
        match message {
            Message::Highlight(h) => self.highlight = h,
        }
    }

    fn view(&self) -> iced::Element<Message> {
        container(
            column![
                MyWidget::new(self.highlight),
                checkbox("Highlight", self.highlight).on_toggle(Message::Highlight),
            ]
            .spacing(20),
        )
        .width(Length::Fill)
        .height(Length::Fill)
        .center_x(Length::Fill)
        .center_y(Length::Fill)
        .into()
    }
}

struct MyWidget {
    highlight: bool,
}

impl MyWidget {
    fn new(highlight: bool) -> Self {
        Self { highlight }
    }
}

impl<Message, Renderer> Widget<Message, Theme, Renderer> for MyWidget
where
    Renderer: iced::advanced::Renderer,
{
    fn size(&self) -> Size<Length> {
        Size {
            width: Length::Shrink,
            height: Length::Shrink,
        }
    }

    fn layout(
        &self,
        _tree: &mut Tree,
        _renderer: &Renderer,
        _limits: &layout::Limits,
    ) -> layout::Node {
        layout::Node::new(iced::Size {
            width: 100.0,
            height: 100.0,
        })
    }

    fn draw(
        &self,
        _state: &Tree,
        renderer: &mut Renderer,
        _theme: &Theme,
        _style: &renderer::Style,
        layout: Layout<'_>,
        _cursor: mouse::Cursor,
        _viewport: &Rectangle,
    ) {
        renderer.fill_quad(
            Quad {
                bounds: layout.bounds(),
                border: Border {
                    color: Color::from_rgb(0.6, 0.8, 1.0),
                    width: 1.0,
                    radius: 10.0.into(),
                },
                shadow: Shadow::default(),
            },
            if self.highlight {
                Color::from_rgb(0.6, 0.8, 1.0)
            } else {
                Color::from_rgb(0.0, 0.2, 0.4)
            },
        );
    }
}

impl<'a, Message, Renderer> From<MyWidget> for Element<'a, Message, Theme, Renderer>
where
    Renderer: iced::advanced::Renderer,
{
    fn from(widget: MyWidget) -> Self {
        Self::new(widget)
    }
}

When highlight is false:

When highlight is true:

➡️ Next: Updating Widgets From Events

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