QCoro 0.7.0 Release Announcement

QCoro 0.7.0 Release Announcement

The major new feature in this release is initial QML support, contributed by Jonah Brüchert. Jonah also contributed QObject::connect helper and a coroutine version of QQuickImageProvider. As always, this release includes some smaller enhancements and bugfixes, you can find a full list of them on the Github release page.

As always, big thank you to everyone who report issues and contributed to QCoro. Your help is much appreciated!

Initial QML Support

Jonah Brüchert has contributed initial support for QML. Unfortunately, we cannot extend the QML engine to support the async and await keywords from ES8, but we can make it possible to set a callback from QML that should be called when the coroutine finishes.

The problem with QCoro::Task is that it is a template class so it cannot be registered into the QML type system and used from inside QML. The solution that Jonach has come up with is to introduce QCoro::QmlTask class, which can wrap any awaitable (be it QCoro::Task or any generic awaitable type) and provides a then() method that can be called from QML and that takes a JavaScript function as its only argument. The function will be invoked by QCoro::QmlTask when the wrapped awaitable has finished.

The disadvantage of this approach is that in order to expose a class that uses QCoro::Task<T> as return types of its member functions into QML, we need to create a wrapper class that converts those return types to QCoro::QmlTask.

Luckily, we should be able to provide a smoother user experience when using QCoro in QML for Qt6 in a future QCoro release.

class QmlCoroTimer: public QObject {
    Q_OBJECT
public:
    explicit QmlCoroTimer(QObject *parent = nullptr)
        : QObject(parent)
    {}

    Q_INVOCABLE QCoro::QmlTask start(int milliseconds) {
        // Implicitly wraps QCoro::Task<> into QCoro::QmlTask
        return waitFor(milliseconds);
    }

private:
    // A simple coroutine that co_awaits a timer timeout
    QCoro::Task<> waitFor(int milliseconds) {
        QTimer timer;
        timer.start(milliseconds);
        co_await timer;
    }
};

...
QCoro::Qml::registerTypes();
qmlRegisterType<QmlCoroTimer>("cz.dvratil.qcoro.example", 0, 1);

import cz.dvratil.qcoro.example 1.0

Item {

    QmlCoroTimer {
        id: timer
    }

    Component.onCompleted: () {
        // Attaches a callback to be called when the QmlCoroTimer::waitFor()
        // coroutine finishes.
        timer.start(1000).then(() => {
            console.log("1 second elapsed!");
        });
    }
}

Read the documentation for QCoro::QmlTask for more details.

QCoro::connect Helper

The QCoro::connect() helper is similar to QObject::connect() - except you you pass in a QCoro::Task<T> instead of a sender and signal pointers. While using the .then() continuation can achieve similar results, the main difference is that QCoro::connect() takes a pointer to a context (receiver) QObject. If the receiver is destroyed before the connected QCoro::Task<T> finishes, the slot is not invoked.

void MyClass::buttonClicked() {
    QCoro::Task<QByteArray> task = sendNetworkRequest();
    // If this object is deleted before the `task` completes,
    // the slot is not invoked.
    QCoro::connect(std::move(task), this, &handleNetworkReply);
}

See the QCoro documentation for more details.

Full changelog

See changelog on Github

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