我有一段在Iced 0.12版本中可以正常运行的代码，现在想要把它升级到Iced 0.14，但遇到了几个编译错误，希望能得到大家的帮助。

原代码（Iced 0.12） #

use iced::widget::{container, text};
use iced::{Application, Color, Command, Element, Settings, Subscription, Theme};
use std::sync::{Arc, Mutex};
use std::thread;
use std::time::Duration;

#[derive(Debug, Clone)]
pub(crate) enum Message {
    ColorChanged(ColorState),
}

#[derive(Debug, Clone, Copy, PartialEq)]
enum ColorState {
    Red,
    Orange,
    Green,
}

impl ColorState {
    fn next(self) -> Self {
        match self {
            ColorState::Red => ColorState::Orange,
            ColorState::Orange => ColorState::Green,
            ColorState::Green => ColorState::Red,
        }
    }

    fn to_color(self) -> Color {
        match self {
            ColorState::Red => Color::from_rgb(0.8, 0.0, 0.0),
            ColorState::Orange => Color::from_rgb(1.0, 0.5, 0.0),
            ColorState::Green => Color::from_rgb(0.0, 0.8, 0.0),
        }
    }

    fn to_text(self) -> &'static str {
        match self {
            ColorState::Red => "Red",
            ColorState::Orange => "Orange",
            ColorState::Green => "Green",
        }
    }
}

struct ColorCycleApp {
    current_color: ColorState,
    color_state: Arc<Mutex<ColorState>>,
}

impl Application for ColorCycleApp {
    type Message = Message;
    type Theme = Theme;
    type Executor = iced::executor::Default;
    type Flags = ();

    fn new(_flags: Self::Flags) -> (Self, Command<Self::Message>) {
        let color_state = Arc::new(Mutex::new(ColorState::Red));

        // Start the background thread
        let color_state_clone = Arc::clone(&color_state);
        thread::spawn(move || {
            loop {
                thread::sleep(Duration::from_secs(2));

                let mut state = color_state_clone.lock().unwrap();
                *state = state.next();
                println!("Thread changed color to: {:?}", *state);
            }
        });

        (
            Self {
                current_color: ColorState::Red,
                color_state,
            },
            Command::none(),
        )
    }

    fn title(&self) -> String {
        String::from("My GUI")
    }

    fn update(&mut self, message: Self::Message) -> Command<Self::Message> {
        match message {
            Message::ColorChanged(new_color) => {
                self.current_color = new_color;
                println!("New color: {:?}", new_color);
                Command::none()
            }
        }
    }

    fn view(&'_ self) -> Element<'_, Self::Message> {
        let current_color = self.current_color.to_color();

        let label = text(self.current_color.to_text()).size(48);

        let colored_container = container(label)
            .width(iced::Length::Fill)
            .height(iced::Length::Fill)
            .center_x()
            .center_y()
            .style(move |_theme: &Theme| container::Appearance {
                background: Some(iced::Background::Color(current_color)),
                ..Default::default()
            });

        colored_container.into()
    }

    fn subscription(&self) -> Subscription<Self::Message> {
        let color_state = Arc::clone(&self.color_state);

        iced::subscription::unfold("color_monitor", ColorState::Red, move |last_color| {
            let color_state = Arc::clone(&color_state);
            async move {
                loop {
                    std::thread::sleep(Duration::from_millis(100));

                    let current_color = {
                        let state = color_state.lock().unwrap();
                        *state
                    };

                    if current_color != last_color {
                        return (Message::ColorChanged(current_color), current_color);
                    }
                }
            }
        })
    }
}

fn main() -> iced::Result {
    ColorCycleApp::run(Settings {
        window: iced::window::Settings {
            size: iced::Size::new(400.0, 300.0),
            ..Default::default()
        },
        ..Default::default()
    })
}

遇到的编译错误 #

• 未解析的导入 iced::Command（Rust 提示我可以使用 std::process::Command 或 tokio::process::Command，但这显然不是我需要的）
• 无法解析：在 iced 根模块中找不到 subscription 相关内容
• 在 container 模块中找不到结构体、变体或联合类型 Appearance
• 编译器提示“期望 trait，却找到结构体 Application”

已尝试的解决方向 #

目前我试过用iced::Program trait来替代原来的Application，也尝试用Container::Style来替换原来的Appearance，但还没能完全解决所有问题，希望有人能帮忙梳理下Iced 0.12到0.14的关键变化，以及这段代码需要做哪些调整才能正常运行。

备注：内容来源于stack exchange，提问作者Josh.h