QMetaObject crate for Rust

The qmetaobject crate is a crate which is used to expose rust object to Qt and QML.

Objectives

• Rust procedural macro (custom derive) to generate a QMetaObject at compile time.
• Bindings for the main Qt types using the cpp! macro from the cpp crate.
• Users of this crate should not require to type any line of C++ or use another build system than cargo.
• Performance: Avoid any unnecessary conversion or heap allocation.

Presentation Blog Post: https://woboq.com/blog/qmetaobject-from-rust.html

Overview

extern crate qmetaobject;
use qmetaobject::*;
#[macro_use] extern crate cstr;

#[derive(QObject,Default)]
struct Greeter {
    base : qt_base_class!(trait QObject),
    name : qt_property!(QString; NOTIFY name_changed),
    name_changed : qt_signal!(),
    compute_greetings : qt_method!(fn compute_greetings(&self, verb : String) -> QString {
        return (verb + " " + &self.name.to_string()).into()
    })
}

fn main() {
    qml_register_type::<Greeter>(cstr!("Greeter"), 1, 0, cstr!("Greeter"));
    let mut engine = QmlEngine::new();
    engine.load_data(r#"import QtQuick 2.6; import QtQuick.Window 2.0;
import Greeter 1.0
Window {
    visible: true;
    Greeter { id: greeter; name: 'World'; }
    Text { anchors.centerIn: parent; text: greeter.compute_greetings('hello'); }
}"#.into());
    engine.exec();

}

Features

• Create object inheriting from QObject, QQuickItem, QAbstractListModel, QQmlExtensionPlugin, ...
• Export Qt properties, signals, methods, ...
• Also support #[derive(QGadget)] (same as Q_GADGET)
• Create Qt plugin (see examples/qmlextensionplugins)
• Partial scene graph support

Requires Qt >= 5.8

What if a binding for the Qt C++ API you want to use is missing?

It is quite likely that you would like to call a particular Qt function wich is not wrapped by this crate.

In this case, it is always possible to access C++ directly from your rust code using the cpp! macro.

Example: from examples/graph/src/main.rs, the struct Graph is a QObject deriving from QQuickItem, QQuickItem::setFlag is currently not exposed in the API but we wish to call it anyway.

impl Graph {
    fn appendSample(&mut self, value: f64) {
        // ...
        let obj = self.get_cpp_object();
        cpp!(unsafe [obj as "QQuickItem*"] { obj->setFlag(QQuickItem::ItemHasContents); });
        // ...
    }
}

But ideally, we should wrap as much as possible so this would not be needed. You can request API as a github issue, or contribute via a pull request.