qt-for-harmonyos-platform-api.qdoc

Go to the documentation of this file.

// Copyright (C) 2026 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
 
/*!
    \page qt-for-harmonyos-platform-api.html
    \title Qt for HarmonyOS Platform API
    \brief Using HarmonyOS platform APIs from a Qt application.
 
    \note Qt's HarmonyOS platform API is in Technology Preview and may
    change in future releases.
 
    A Qt application can call HarmonyOS ArkTS APIs directly. This
    documentation calls them platform APIs. Use them for features that Qt
    does not cover, such as showing the system share sheet, making an
    in-app purchase, or refreshing the application's home-screen widgets.
    Qt does not wrap these APIs.
 
    On HarmonyOS, the ArkTS runtime and the platform UI run on the main
    thread of the process. This documentation refers to this thread as the
    JS thread, and to the objects of the ArkTS runtime as JS objects. Qt
    runs the application on a separate thread, called the Qt thread.
 
    Qt provides the following classes and functions for calling platform
    APIs:
 
    \list
    \li QNativeInterface::QHarmonyApplication runs code on the JS thread,
        where the platform APIs are available, and brings results back to
        the Qt thread. The code receives a QHarmonyJsContext.
    \li QHarmonyJsContext provides the Node-API environment and loads JS
        modules by name.
    \li QHarmonyAppJsContext gives access to application-level JS objects,
        such as the default \c UIAbility instance.
    \li QHarmonyJsObjectRef keeps a JS object alive. You can store, copy,
        and compare the reference on any thread, but you can access the
        object only on the JS thread.
    \li The QtHarmony namespace contains free functions for code that runs
        on the JS thread, such as conversions between QJsonObject and JS
        objects.
    \endlist
 
    Qt's HarmonyOS platform API uses the C Node-API types \c napi_env and
    \c napi_value. They are part of the HarmonyOS SDK and have a stable ABI.
    Node-API is a low-level, weakly typed C API that requires manual error
    handling and resource management. It is strongly recommended that
    applications use
    \l {https://github.com/nodejs/node-addon-api}{node-addon-api}, the
    header-only C++ wrapper for Node-API that the Node.js project publishes.
    Its types convert to and from the C types at no cost. The snippet in
    the next section uses it.
 
    \section1 The Two Threads
 
    The Qt thread is the thread of the QCoreApplication object, which runs
    the Qt event loop. Platform APIs are available only on the JS thread. To
    run code there, pass it as a task to
    QNativeInterface::QHarmonyApplication::runOnJsThread():
 
    \code
    const QJsonObject vibrationEffect{
        {"type", "time"},
        {"duration", 200},
    };
    const QJsonObject vibrationAttribute{
        {"usage", "touch"},
    };
 
    // ...
 
    QNativeInterface::QHarmonyApplication::runOnJsThread(
        [vibrationEffect, vibrationAttribute](QHarmonyJsContext &jsContext) {
            Napi::Env env(jsContext.env());
            Napi::Object vibratorModule(env, jsContext.tryImportModule("@ohos.vibrator"));
            if (vibratorModule.IsEmpty())
                return;
 
            Napi::Object jsVibrationEffect(env, QtHarmony::mapQJsonObjectToJsObject(env, vibrationEffect));
            Napi::Object jsVibrationAttribute(env, QtHarmony::mapQJsonObjectToJsObject(env, vibrationAttribute));
 
            auto startVibrationFunc = vibratorModule.Get("startVibration").As<Napi::Function>();
            auto startVibrationPromise = startVibrationFunc.Call(vibratorModule, {jsVibrationEffect, jsVibrationAttribute}).As<Napi::Object>();
            startVibrationPromise.Get("then").As<Napi::Function>().Call(
                startVibrationPromise,
                {
                    Napi::Function::New(
                        env,
                        [](const Napi::CallbackInfo &) {
                            qDebug() << "startVibration() succeeded";
                        }),
                    Napi::Function::New(
                        env,
                        [](const Napi::CallbackInfo &info) {
                            qWarning() << "startVibration() failed:" << QString::fromStdString(info[0].ToString());
                        }),
                });
        });
    \endcode
 
    Code that runs on the JS thread must follow the rules listed in the
    QNativeInterface::QHarmonyApplication documentation. To send results
    back to the Qt thread, use
    QNativeInterface::QHarmonyApplication::runOnQtThread(). To pass JS data
    to the Qt thread, convert it to a QJsonObject with
    QtHarmony::mapJsObjectToQJsonObject(), or keep it in a
    QHarmonyJsObjectRef.
 
    \section1 JS Callbacks
 
    Asynchronous platform APIs return promises or take callbacks. To handle
    a promise or to pass a callback, create a function with
    \c napi_create_function(). Such a function receives the \c napi_env, but
    not a QHarmonyJsContext. To get the context, call
    QHarmonyJsContext::fromEnv(). These functions run on the JS thread and
    follow the same rules as tasks passed to
    QNativeInterface::QHarmonyApplication::runOnJsThread().
 
    \section1 JS Modules
 
    QHarmonyJsContext::tryImportModule() returns a JS module by name, for
    example \c {@ohos.app.ability.AbilityConstant}. It loads the module on
    first use. Enumerations are properties of the module object or of a
    namespace in it. For example, \c LaunchReason is a property of the
    \c {@ohos.app.ability.AbilityConstant} module object. Enumeration
    values are properties of their enumeration.
 
    Native code cannot load kits, the \c {@kit.*} modules. The ArkTS
    application template bundled with Qt makes the kit modules that Qt
    needs available to native code. QHarmonyJsContext::tryImportModule()
    accepts their names, such as \c {@kit.ShareKit.systemShare}.
 
    \section1 Platform API Examples
 
    \list
    \li \l {Qt for HarmonyOS Restart Application Example}
    \li \l {Qt for HarmonyOS Notification Example}
    \endlist
*/