实现目标：在输入框中输入文本，通过指定热键，弹出菜单。

use fltk::{
    enums::{Event, Key},
    prelude::*,
    *,
};

fn main() {
    let app = app::App::default();
    let mut window = window::DoubleWindow::new(100, 100, 300, 200, "Menu in text editor");
    let mut menu = menu::MenuButton::default().with_type(menu::MenuButtonType::Popup3);
    menu.add_choice("Hello|Hi|You");
    let mut editor = text::TextEditor::new(20, 20, 260, 160, "");
    let buf = text::TextBuffer::default();
    editor.set_buffer(buf.clone());

    editor.handle(move |te, ev| match ev {
        Event::KeyDown => {
            if app::event_key_down(Key::AltL) {
                if let Some(item) = menu.popup() {
                    if let Some(label) = item.label() {
                        te.insert(&label);
                    }
                }
                println!("{}", buf.line_text(te.insert_position()));
            }
            true
        }
        _ => false,
    });
    window.end();
    window.show();
    while app.wait() {}
}