Group widgets

These are container widgets which include Window types and others found in the group module: Group, Scroll, Pack, Tile, Flex ...etc. Widgets implementing the GroupExt trait, are characterized by having to call ::end() method to basically close them.

use fltk::{
    app,
    button::Button,
    prelude::{GroupExt, WidgetBase, WidgetExt},
    window::Window,
};

fn main() {
    let a = app::App::default();
    let mut win = Window::default().with_size(400, 300);
    let _btn = Button::new(160, 200, 80, 30, "Click");
    win.end();
    win.show();
    a.run().unwrap();
}

In the above example, the button btn will be parented by the window. After ending such GroupExt widgets, any other widgets instantiated after the end call, will be instantiated outside. These can still be added using the ::add(&other_widget) method (or using ::insert):

use fltk::{
    app,
    button::Button,
    prelude::{GroupExt, WidgetBase, WidgetExt},
    window::Window,
};

fn main() {
    let a = app::App::default();
    let mut win = Window::default().with_size(400, 300);
    win.end();
    win.show();

    let btn = Button::new(160, 200, 80, 30, "Click");
    win.add(&btn);
    
    a.run().unwrap();
}

Another option is to reopen the widget:

use fltk::{
    app,
    button::Button,
    prelude::{GroupExt, WidgetBase, WidgetExt},
    window::Window,
};

fn main() {
    let a = app::App::default();
    let mut win = Window::default().with_size(400, 300);
    win.end();
    win.show();

    win.begin();
    let _btn = Button::new(160, 200, 80, 30, "Click");
    win.end();

    a.run().unwrap();
}

While most GroupExt widgets require manual layouts, several have automatic layouting. The Flex widget was discussed in the layouts page. Packs require the width or height of the child widget, depending on the Pack's orientation.

A vertical Pack needs to know only the heights of its children:

use fltk::{prelude::*, *};

fn main() {
    let app = app::App::default();
    let mut wind = window::Window::default().with_size(200, 300);
    let mut pack = group::Pack::default_fill();
    pack.set_spacing(5);
    for i in 0..2 {
        frame::Frame::default().with_size(0, 40).with_label(&format!("field {}", i));
        input::Input::default().with_size(0, 40);
    }
    frame::Frame::default().with_size(0, 40); // a filler
    button::Button::default().with_size(0, 40).with_label("Submit");
    pack.end();
    wind.end();
    wind.show();

    app.run().unwrap();
}

For a horizontal pack, we set the Pack type, then we only need to pass the widths of the children:

use fltk::{prelude::*, *};

fn main() {
    let app = app::App::default();
    let mut wind = window::Window::default().with_size(300, 100);
    let mut pack = group::Pack::default_fill().with_type(group::PackType::Horizontal);
    pack.set_spacing(5);
    for i in 0..2 {
        frame::Frame::default().with_size(40, 0).with_label(&format!("field {}", i));
        input::Input::default().with_size(40, 0);
    }
    frame::Frame::default().with_size(40, 0); // a filler
    button::Button::default().with_size(40, 0).with_label("Submit");
    pack.end();
    wind.end();
    wind.show();

    app.run().unwrap();
}