server emit signal example about dbus-rs

[diwic]

Hi! I added "sending a signal" to my existing server example. While I did that I realized that there are some room to make things work more ergonomic. Anyhow, here's something that works for now:

extern crate dbus;

use std::cell::RefCell;
use std::sync::Arc;
use dbus::{Connection, BusType, NameFlag};
use dbus::tree::{Factory, Signal};

fn main() {
    let c = Connection::get_private(BusType::Session).unwrap();
    c.register_name("com.example.dbustest", NameFlag::ReplaceExisting as u32).unwrap();

    let f = Factory::new_fn();
    let signal: RefCell<Option<Arc<Signal>>> = RefCell::new(None);
    let tree = f.tree().add(f.object_path("/hello").introspectable().add({
        let mut i = f.interface("com.example.dbustest").add_m(
            f.method("Hello", |m,_,_| {
                let s = format!("Hello {}!", m.sender().unwrap());
                Ok(vec!(m.method_return().append1(s), signal.borrow().as_ref().unwrap().emit(&[])))
            }).outarg::<&str,_>("reply") // One output argument, no input arguments
        );
        *signal.borrow_mut() = Some(i.add_s_ref(f.signal("HelloHappened")));
        i
    }));

    tree.set_registered(&c, true).unwrap();
    for _ in tree.run(&c, c.iter(1000)) {}
}

[diwic]

...and the committed code now includes a slightly more ergonomic example (which avoids RefCell<Option<>>) which uses some just added API.

[sbwtw]

thanks a lot !