qjniobject.h

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// Copyright (C) 2022 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
#ifndef QJNIOBJECT_H
#define QJNIOBJECT_H
 
#include <QtCore/qsharedpointer.h>
 
#if defined(Q_QDOC) || defined(Q_OS_ANDROID)
#include <jni.h>
#include <QtCore/qjnienvironment.h>
 
QT_BEGIN_NAMESPACE
 
class QJniObjectPrivate;
 
class Q_CORE_EXPORT QJniObject
{
    friend class QJniArrayBase;
 
    template <typename ...Args>
    struct LocalFrame {
        mutable JNIEnv *env;
        bool hasFrame = false;
        explicit LocalFrame(JNIEnv *env = nullptr) noexcept
            : env(env)
        {
        }
        ~LocalFrame()
        {
            if (hasFrame)
                env->PopLocalFrame(nullptr);
        }
        template <typename T>
        auto newLocalRef(jobject object)
        {
            if (!hasFrame) {
                if (jniEnv()->PushLocalFrame(sizeof...(Args)) < 0)
                    return T{}; // JVM is out of memory, avoid making matters worse
                hasFrame = true;
            }
            return static_cast<T>(jniEnv()->NewLocalRef(object));
        }
        template <typename T>
        auto newLocalRef(const QJniObject &object)
        {
            return newLocalRef<T>(object.template object<T>());
        }
        JNIEnv *jniEnv() const
        {
            if (!env)
                env = QJniEnvironment::getJniEnv();
            return env;
        }
        bool checkAndClearExceptions()
        {
            return env ? QJniEnvironment::checkAndClearExceptions(env) : false;
        }
        template <typename T>
        auto convertToJni(T &&value);
        template <typename T>
        auto convertFromJni(QJniObject &&object);
    };
public:
    QJniObject();
    explicit QJniObject(const char *className);
    explicit QJniObject(const char *className, const char *signature, ...);
    template<typename ...Args
#ifndef Q_QDOC
        , std::enable_if_t<!std::disjunction_v<QtJniTypes::IsStringType<std::decay_t<Args>>...>>* = nullptr
#endif
        >
    explicit QJniObject(const char *className, Args &&...args)
        : QJniObject(LocalFrame<Args...>{}, className, std::forward<Args>(args)...)
    {
    }
private:
    template<typename ...Args>
    explicit QJniObject(LocalFrame<Args...> localFrame, const char *className, Args &&...args)
        : QJniObject(className, QtJniTypes::constructorSignature<Args...>().data(),
                     localFrame.convertToJni(std::forward<Args>(args))...)
    {
    }
public:
    explicit QJniObject(jclass clazz);
    explicit QJniObject(jclass clazz, const char *signature, ...);
    template<typename ...Args
#ifndef Q_QDOC
        , std::enable_if_t<!std::disjunction_v<QtJniTypes::IsStringType<std::decay_t<Args>>...>>* = nullptr
#endif
        >
    explicit QJniObject(jclass clazz, Args &&...args)
        : QJniObject(clazz, QtJniTypes::constructorSignature<Args...>().data(),
                     std::forward<Args>(args)...)
    {}
    QJniObject(jobject globalRef);
 
    QJniObject(const QJniObject &other) noexcept = default;
    QJniObject(QJniObject &&other) noexcept = default;
    QJniObject &operator=(const QJniObject &other) noexcept = default;
    QJniObject &operator=(QJniObject &&other) noexcept = default;
 
    ~QJniObject();
 
    template<typename Class, typename ...Args>
    static inline QJniObject construct(Args &&...args)
    {
        LocalFrame<Args...> frame;
        return QJniObject(QtJniTypes::Traits<Class>::className().data(),
                          QtJniTypes::constructorSignature<Args...>().data(),
                          frame.convertToJni(std::forward<Args>(args))...);
    }
 
    jobject object() const;
    template <typename T> T object() const
    {
        QtJniTypes::assertObjectType<T>();
        return static_cast<T>(javaObject());
    }
 
    jclass objectClass() const;
    QByteArray className() const;
 
    template <typename Ret, typename ...Args
#ifndef Q_QDOC
        , QtJniTypes::IfValidFieldType<Ret> = true
#endif
    >
    auto callMethod(const char *methodName, const char *signature, Args &&...args) const
    {
        LocalFrame<Args...> frame(jniEnv());
        if constexpr (QtJniTypes::isObjectType<Ret>()) {
            return frame.template convertFromJni<Ret>(callObjectMethod(methodName, signature,
                                                frame.convertToJni(std::forward<Args>(args))...));
        } else {
            jmethodID id = getCachedMethodID(frame.jniEnv(), methodName, signature);
            if (id) {
                if constexpr (std::is_same_v<Ret, void>) {
                    callVoidMethodV(frame.jniEnv(), id,
                                    frame.convertToJni(std::forward<Args>(args))...);
                    frame.checkAndClearExceptions();
                } else {
                    Ret res{};
                    callMethodForType<Ret>(frame.jniEnv(), res, object(), id,
                                           frame.convertToJni(std::forward<Args>(args))...);
                    if (frame.checkAndClearExceptions())
                        res = {};
                    return res;
                }
            }
            if constexpr (!std::is_same_v<Ret, void>)
                return Ret{};
        }
    }
 
    template <typename Ret, typename ...Args
#ifndef Q_QDOC
        , QtJniTypes::IfValidSignatureTypes<Ret, Args...> = true
#endif
    >
    auto callMethod(const char *methodName, Args &&...args) const
    {
        constexpr auto signature = QtJniTypes::methodSignature<Ret, Args...>();
        return callMethod<Ret>(methodName, signature.data(), std::forward<Args>(args)...);
    }
 
    template <typename Ret, typename ...Args
#ifndef Q_QDOC
        , QtJniTypes::IfValidSignatureTypes<Ret, Args...> = true
#endif
    >
    QJniObject callObjectMethod(const char *methodName, Args &&...args) const
    {
        QtJniTypes::assertObjectType<Ret>();
        constexpr auto signature = QtJniTypes::methodSignature<Ret, Args...>();
        LocalFrame<Args...> frame(jniEnv());
        return frame.template convertFromJni<Ret>(callObjectMethod(methodName, signature,
                                            frame.convertToJni(std::forward<Args>(args))...));
    }
 
    QJniObject callObjectMethod(const char *methodName, const char *signature, ...) const;
 
    template <typename Ret, typename ...Args>
    static auto callStaticMethod(const char *className, const char *methodName, const char *signature, Args &&...args)
    {
        JNIEnv *env = QJniEnvironment::getJniEnv();
        jclass clazz = QJniObject::loadClass(className, env);
        return callStaticMethod<Ret>(clazz, methodName, signature, std::forward<Args>(args)...);
    }
 
    template <typename Ret, typename ...Args>
    static auto callStaticMethod(jclass clazz, const char *methodName, const char *signature, Args &&...args)
    {
        JNIEnv *env = QJniEnvironment::getJniEnv();
        jmethodID id = clazz ? getMethodID(env, clazz, methodName, signature, true)
                             : 0;
        return callStaticMethod<Ret>(clazz, id, std::forward<Args>(args)...);
    }
 
    template <typename Ret, typename ...Args
#ifndef Q_QDOC
        , QtJniTypes::IfValidFieldType<Ret> = true
#endif
    >
    static auto callStaticMethod(jclass clazz, jmethodID methodId, Args &&...args)
    {
        LocalFrame<Args...> frame;
        if constexpr (QtJniTypes::isObjectType<Ret>()) {
            return frame.template convertFromJni<Ret>(callStaticObjectMethod(clazz, methodId,
                                                frame.convertToJni(std::forward<Args>(args))...));
        } else {
            if (clazz && methodId) {
                if constexpr (std::is_same_v<Ret, void>) {
                    callStaticMethodForVoid(frame.jniEnv(), clazz, methodId,
                                            frame.convertToJni(std::forward<Args>(args))...);
                    frame.checkAndClearExceptions();
                } else {
                    Ret res{};
                    callStaticMethodForType<Ret>(frame.jniEnv(), res, clazz, methodId,
                                                 frame.convertToJni(std::forward<Args>(args))...);
                    if (frame.checkAndClearExceptions())
                        res = {};
                    return res;
                }
            }
            if constexpr (!std::is_same_v<Ret, void>)
                return Ret{};
        }
    }
 
    template <typename Ret, typename ...Args
#ifndef Q_QDOC
        , QtJniTypes::IfValidSignatureTypes<Ret, Args...> = true
#endif
    >
    static auto callStaticMethod(const char *className, const char *methodName, Args &&...args)
    {
        JNIEnv *env = QJniEnvironment::getJniEnv();
        jclass clazz = QJniObject::loadClass(className, env);
        const jmethodID id = clazz ? getMethodID(env, clazz, methodName,
                                         QtJniTypes::methodSignature<Ret, Args...>().data(), true)
                                   : 0;
        return callStaticMethod<Ret>(clazz, id, std::forward<Args>(args)...);
    }
 
    template <typename Ret, typename ...Args
#ifndef Q_QDOC
        , QtJniTypes::IfValidSignatureTypes<Ret, Args...> = true
#endif
    >
    static auto callStaticMethod(jclass clazz, const char *methodName, Args &&...args)
    {
        constexpr auto signature = QtJniTypes::methodSignature<Ret, Args...>();
        return callStaticMethod<Ret>(clazz, methodName, signature.data(), std::forward<Args>(args)...);
    }
    template <typename Klass, typename Ret, typename ...Args
#ifndef Q_QDOC
        , QtJniTypes::IfValidSignatureTypes<Ret, Args...> = true
#endif
    >
    static auto callStaticMethod(const char *methodName, Args &&...args)
    {
        JNIEnv *env = QJniEnvironment::getJniEnv();
        const jclass clazz = QJniObject::loadClass(QtJniTypes::Traits<Klass>::className().data(),
                                                   env);
        const jmethodID id = clazz ? getMethodID(env, clazz, methodName,
                                         QtJniTypes::methodSignature<Ret, Args...>().data(), true)
                                   : 0;
        return callStaticMethod<Ret>(clazz, id, std::forward<Args>(args)...);
    }
 
    static QJniObject callStaticObjectMethod(const char *className, const char *methodName,
                                             const char *signature, ...);
 
    static QJniObject callStaticObjectMethod(jclass clazz, const char *methodName,
                                             const char *signature, ...);
 
    static QJniObject callStaticObjectMethod(jclass clazz, jmethodID methodId, ...);
 
 
    template <typename Ret, typename ...Args
#ifndef Q_QDOC
        , QtJniTypes::IfValidSignatureTypes<Ret, Args...> = true
#endif
    >
    static QJniObject callStaticObjectMethod(const char *className, const char *methodName, Args &&...args)
    {
        QtJniTypes::assertObjectType<Ret>();
        constexpr auto signature = QtJniTypes::methodSignature<Ret, Args...>();
        LocalFrame<Args...> frame;
        return frame.template convertFromJni<Ret>(callStaticObjectMethod(className, methodName, signature.data(),
                                            frame.convertToJni(std::forward<Args>(args))...));
    }
 
    template <typename Ret, typename ...Args
#ifndef Q_QDOC
        , QtJniTypes::IfValidSignatureTypes<Ret, Args...> = true
#endif
    >
    static QJniObject callStaticObjectMethod(jclass clazz, const char *methodName, Args &&...args)
    {
        QtJniTypes::assertObjectType<Ret>();
        constexpr auto signature = QtJniTypes::methodSignature<Ret, Args...>();
        LocalFrame<Args...> frame;
        return frame.template convertFromJni<Ret>(callStaticObjectMethod(clazz, methodName, signature.data(),
                                            frame.convertToJni(std::forward<Args>(args))...));
    }
 
    template <typename T
#ifndef Q_QDOC
        , QtJniTypes::IfValidFieldType<T> = true
#endif
    >
    auto getField(const char *fieldName) const
    {
        LocalFrame<T> frame(jniEnv());
        if constexpr (QtJniTypes::isObjectType<T>()) {
            return frame.template convertFromJni<T>(getObjectField<T>(fieldName));
        } else {
            T res{};
            constexpr auto signature = QtJniTypes::fieldSignature<T>();
            jfieldID id = getCachedFieldID(frame.jniEnv(), fieldName, signature);
            if (id) {
                getFieldForType<T>(frame.jniEnv(), res, object(), id);
                if (frame.checkAndClearExceptions())
                    res = {};
            }
            return res;
        }
    }
 
    template <typename T
#ifndef Q_QDOC
        , QtJniTypes::IfValidFieldType<T> = true
#endif
    >
    static auto getStaticField(const char *className, const char *fieldName)
    {
        LocalFrame<T> frame;
        if constexpr (QtJniTypes::isObjectType<T>()) {
            return frame.template convertFromJni<T>(getStaticObjectField<T>(className, fieldName));
        } else {
            jclass clazz = QJniObject::loadClass(className, frame.jniEnv());
            if (!clazz)
                return T{};
            return getStaticField<T>(clazz, fieldName);
        }
    }
 
    template <typename T
#ifndef Q_QDOC
        , QtJniTypes::IfValidFieldType<T> = true
#endif
    >
    static auto getStaticField(jclass clazz, const char *fieldName)
    {
        LocalFrame<T> frame;
        if constexpr (QtJniTypes::isObjectType<T>()) {
            return frame.template convertFromJni<T>(getStaticObjectField<T>(clazz, fieldName));
        } else {
            T res{};
            constexpr auto signature = QtJniTypes::fieldSignature<T>();
            jfieldID id = getFieldID(frame.jniEnv(), clazz, fieldName, signature, true);
            if (id) {
                getStaticFieldForType<T>(frame.jniEnv(), res, clazz, id);
                if (frame.checkAndClearExceptions())
                    res = {};
            }
            return res;
        }
    }
 
    template <typename Klass, typename T
#ifndef Q_QDOC
        , QtJniTypes::IfValidFieldType<T> = true
#endif
    >
    static auto getStaticField(const char *fieldName)
    {
        return getStaticField<T>(QtJniTypes::Traits<Klass>::className(), fieldName);
    }
 
    template <typename T
#ifndef Q_QDOC
        , std::enable_if_t<QtJniTypes::isObjectType<T>(), bool> = true
#endif
    >
    QJniObject getObjectField(const char *fieldName) const
    {
        constexpr auto signature = QtJniTypes::fieldSignature<T>();
        return getObjectField(fieldName, signature);
    }
 
    QJniObject getObjectField(const char *fieldName, const char *signature) const;
 
    template <typename T
#ifndef Q_QDOC
        , std::enable_if_t<QtJniTypes::isObjectType<T>(), bool> = true
#endif
    >
    static QJniObject getStaticObjectField(const char *className, const char *fieldName)
    {
        constexpr auto signature = QtJniTypes::fieldSignature<T>();
        return getStaticObjectField(className, fieldName, signature);
    }
 
    static QJniObject getStaticObjectField(const char *className,
                                           const char *fieldName,
                                           const char *signature);
 
    template <typename T
#ifndef Q_QDOC
        , std::enable_if_t<QtJniTypes::isObjectType<T>(), bool> = true
#endif
    >
    static QJniObject getStaticObjectField(jclass clazz, const char *fieldName)
    {
        constexpr auto signature = QtJniTypes::fieldSignature<T>();
        return getStaticObjectField(clazz, fieldName, signature);
    }
 
    static QJniObject getStaticObjectField(jclass clazz, const char *fieldName,
                                           const char *signature);
 
    template <typename T
#ifndef Q_QDOC
        , QtJniTypes::IfValidFieldType<T> = true
#endif
    >
    void setField(const char *fieldName, T value)
    {
        constexpr auto signature = QtJniTypes::fieldSignature<T>();
        jfieldID id = getCachedFieldID(jniEnv(), fieldName, signature);
        if (id) {
            setFieldForType<T>(jniEnv(), object(), id, value);
            QJniEnvironment::checkAndClearExceptions(jniEnv());
        }
    }
 
    template <typename T
#ifndef Q_QDOC
        , QtJniTypes::IfValidFieldType<T> = true
#endif
    >
    void setField(const char *fieldName, const char *signature, T value)
    {
        jfieldID id = getCachedFieldID(jniEnv(), fieldName, signature);
        if (id) {
            setFieldForType<T>(jniEnv(), object(), id, value);
            QJniEnvironment::checkAndClearExceptions(jniEnv());
        }
    }
 
    template <typename T
#ifndef Q_QDOC
        , QtJniTypes::IfValidFieldType<T> = true
#endif
    >
    static void setStaticField(const char *className, const char *fieldName, T value)
    {
        LocalFrame<T> frame;
        jclass clazz = QJniObject::loadClass(className, frame.jniEnv());
        if (!clazz)
            return;
 
        constexpr auto signature = QtJniTypes::fieldSignature<T>();
        jfieldID id = getCachedFieldID(frame.jniEnv(), clazz, className, fieldName,
                                       signature, true);
        if (!id)
            return;
 
        setStaticFieldForType<T>(frame.jniEnv(), clazz, id, value);
        frame.checkAndClearExceptions();
    }
 
    template <typename T
#ifndef Q_QDOC
        , QtJniTypes::IfValidFieldType<T> = true
#endif
    >
    static void setStaticField(const char *className, const char *fieldName,
                               const char *signature, T value)
    {
        JNIEnv *env = QJniEnvironment::getJniEnv();
        jclass clazz = QJniObject::loadClass(className, env);
 
        if (!clazz)
            return;
 
        jfieldID id = getCachedFieldID(env, clazz, className, fieldName,
                                       signature, true);
        if (id) {
            setStaticFieldForType<T>(env, clazz, id, value);
            QJniEnvironment::checkAndClearExceptions(env);
        }
    }
 
    template <typename T
#ifndef Q_QDOC
        , QtJniTypes::IfValidFieldType<T> = true
#endif
    >
    static void setStaticField(jclass clazz, const char *fieldName,
                               const char *signature, T value)
    {
        JNIEnv *env = QJniEnvironment::getJniEnv();
        jfieldID id = getFieldID(env, clazz, fieldName, signature, true);
 
        if (id) {
            setStaticFieldForType<T>(env, clazz, id, value);
            QJniEnvironment::checkAndClearExceptions(env);
        }
    }
 
    template <typename T
#ifndef Q_QDOC
        , QtJniTypes::IfValidFieldType<T> = true
#endif
    >
    static void setStaticField(jclass clazz, const char *fieldName, T value)
    {
        setStaticField(clazz, fieldName, QtJniTypes::fieldSignature<T>(), value);
    }
 
    template <typename Klass, typename T
#ifndef Q_QDOC
        , QtJniTypes::IfValidFieldType<T> = true
#endif
    >
    static void setStaticField(const char *fieldName, T value)
    {
        setStaticField(QtJniTypes::Traits<Klass>::className(), fieldName, value);
    }
 
    static QJniObject fromString(const QString &string);
    QString toString() const;
 
    static bool isClassAvailable(const char *className);
    bool isValid() const;
 
    // This function takes ownership of the jobject and releases the local ref. before returning.
    static QJniObject fromLocalRef(jobject lref);
 
    template <typename T,
              std::enable_if_t<std::is_convertible_v<T, jobject>, bool> = true>
    QJniObject &operator=(T obj)
    {
        assign(static_cast<T>(obj));
        return *this;
    }
 
protected:
    QJniObject(Qt::Initialization) {}
    JNIEnv *jniEnv() const noexcept;
 
private:
    static jclass loadClass(const QByteArray &className, JNIEnv *env);
 
#if QT_CORE_REMOVED_SINCE(6, 7)
    // these need to stay in the ABI as they were used in inline methods before 6.7
    static jclass loadClass(const QByteArray &className, JNIEnv *env, bool binEncoded);
    static QByteArray toBinaryEncClassName(const QByteArray &className);
    void callVoidMethodV(JNIEnv *env, jmethodID id, va_list args) const;
#endif
 
    static jfieldID getCachedFieldID(JNIEnv *env, jclass clazz, const QByteArray &className,
                                     const char *name, const char *signature,
                                     bool isStatic = false);
    jfieldID getCachedFieldID(JNIEnv *env, const char *name, const char *signature,
                              bool isStatic = false) const;
    static jmethodID getCachedMethodID(JNIEnv *env, jclass clazz, const QByteArray &className,
                                       const char *name, const char *signature,
                                       bool isStatic = false);
    jmethodID getCachedMethodID(JNIEnv *env, const char *name, const char *signature,
                                bool isStatic = false) const;
 
    static jfieldID getFieldID(JNIEnv *env, jclass clazz, const char *name,
                               const char *signature, bool isStatic = false);
    static jmethodID getMethodID(JNIEnv *env, jclass clazz, const char *name,
                                 const char *signature, bool isStatic = false);
 
    void callVoidMethodV(JNIEnv *env, jmethodID id, ...) const;
 
    bool isSameObject(jobject obj) const;
    bool isSameObject(const QJniObject &other) const;
    void assign(jobject obj);
    jobject javaObject() const;
 
    friend bool operator==(const QJniObject &, const QJniObject &);
    friend bool operator!=(const QJniObject&, const QJniObject&);
 
    template<typename T>
    static constexpr void callMethodForType(JNIEnv *env, T &res, jobject obj, jmethodID id, ...)
    {
        va_list args = {};
        va_start(args, id);
        QtJniTypes::Caller<T>::callMethodForType(env, res, obj, id, args);
        va_end(args);
    }
 
    template<typename T>
    static constexpr void callStaticMethodForType(JNIEnv *env, T &res, jclass clazz,
                                                  jmethodID id, ...)
    {
        if (!clazz || !id)
            return;
        va_list args = {};
        va_start(args, id);
        QtJniTypes::Caller<T>::callStaticMethodForType(env, res, clazz, id, args);
        va_end(args);
    }
 
    static void callStaticMethodForVoid(JNIEnv *env, jclass clazz, jmethodID id, ...)
    {
        if (!clazz || !id)
            return;
        va_list args;
        va_start(args, id);
        env->CallStaticVoidMethodV(clazz, id, args);
        va_end(args);
    }
 
 
    template<typename T>
    static constexpr void getFieldForType(JNIEnv *env, T &res, jobject obj, jfieldID id)
    {
        QtJniTypes::Caller<T>::getFieldForType(env, res, obj, id);
    }
 
    template<typename T>
    static constexpr void getStaticFieldForType(JNIEnv *env, T &res, jclass clazz, jfieldID id)
    {
        QtJniTypes::Caller<T>::getStaticFieldForType(env, res, clazz, id);
    }
 
    template<typename T>
    static constexpr void setFieldForType(JNIEnv *env, jobject obj, jfieldID id, T value)
    {
        if constexpr (QtJniTypes::isObjectType<T>()) {
            LocalFrame<T> frame(env);
            env->SetObjectField(obj, id, static_cast<jobject>(frame.convertToJni(value)));
        } else {
            QtJniTypes::Caller<T>::setFieldForType(env, obj, id, value);
        }
    }
 
    template<typename T>
    static constexpr void setStaticFieldForType(JNIEnv *env, jclass clazz, jfieldID id, T value)
    {
        if constexpr (QtJniTypes::isObjectType<T>()) {
            LocalFrame<T> frame(env);
            env->SetStaticObjectField(clazz, id, static_cast<jobject>(frame.convertToJni(value)));
        } else {
            QtJniTypes::Caller<T>::setStaticFieldForType(env, clazz, id, value);
        }
    }
 
    friend QJniObjectPrivate;
    QSharedPointer<QJniObjectPrivate> d;
};
 
inline bool operator==(const QJniObject &obj1, const QJniObject &obj2)
{
    return obj1.isSameObject(obj2);
}
 
inline bool operator!=(const QJniObject &obj1, const QJniObject &obj2)
{
    return !obj1.isSameObject(obj2);
}
 
namespace QtJniTypes {
struct QT_TECH_PREVIEW_API JObjectBase
{
    operator QJniObject() const { return m_object; }
 
    bool isValid() const { return m_object.isValid(); }
    jclass objectClass() const { return m_object.objectClass(); }
    QString toString() const { return m_object.toString(); }
 
    template <typename T = jobject>
    T object() const {
        return m_object.object<T>();
    }
 
protected:
    JObjectBase() = default;
    ~JObjectBase() = default;
 
    Q_IMPLICIT JObjectBase(jobject object) : m_object(object) {}
    Q_IMPLICIT JObjectBase(const QJniObject &object) : m_object(object) {}
    Q_IMPLICIT JObjectBase(QJniObject &&object) noexcept : m_object(std::move(object)) {}
 
    QJniObject m_object;
};
 
template<typename Type>
class QT_TECH_PREVIEW_API JObject : public JObjectBase
{
public:
    using Class = Type;
 
    JObject()
        : JObjectBase{QJniObject(QtJniTypes::Traits<Class>::className())}
    {}
    Q_IMPLICIT JObject(jobject object) : JObjectBase(object) {}
    Q_IMPLICIT JObject(const QJniObject &object) : JObjectBase(object) {}
    Q_IMPLICIT JObject(QJniObject &&object) noexcept : JObjectBase(std::move(object)) {}
 
    // base class destructor is protected, so need to provide all SMFs
    JObject(const JObject &other) = default;
    JObject(JObject &&other) noexcept = default;
    JObject &operator=(const JObject &other) = default;
    JObject &operator=(JObject &&other) noexcept = default;
 
    ~JObject() = default;
 
    template<typename Arg, typename ...Args
            , std::enable_if_t<!std::is_same_v<Arg, JObject>, bool> = true
            , IfValidSignatureTypes<Arg, Args...> = true
    >
    explicit JObject(Arg && arg, Args &&...args)
        : JObjectBase{QJniObject(QtJniTypes::Traits<Class>::className(),
                                 std::forward<Arg>(arg), std::forward<Args>(args)...)}
    {}
 
    // named constructors avoid ambiguities
    static Type fromJObject(jobject object) { return Type(object); }
    template <typename ...Args>
    static Type construct(Args &&...args) { return Type(std::forward<Args>(args)...); }
    static Type fromLocalRef(jobject lref) { return Type(QJniObject::fromLocalRef(lref)); }
 
    static bool registerNativeMethods(std::initializer_list<JNINativeMethod> methods)
    {
        QJniEnvironment env;
        return env.registerNativeMethods<Class>(methods);
    }
 
    // public API forwarding to QJniObject, with the implicit Class template parameter
    template <typename Ret, typename ...Args
#ifndef Q_QDOC
        , QtJniTypes::IfValidSignatureTypes<Ret, Args...> = true
#endif
    >
    static auto callStaticMethod(const char *name, Args &&...args)
    {
        return QJniObject::callStaticMethod<Class, Ret, Args...>(name,
                                                                 std::forward<Args>(args)...);
    }
    template <typename T
#ifndef Q_QDOC
        , QtJniTypes::IfValidFieldType<T> = true
#endif
    >
    static auto getStaticField(const char *field)
    {
        return QJniObject::getStaticField<Class, T>(field);
    }
    template <typename T
#ifndef Q_QDOC
        , QtJniTypes::IfValidFieldType<T> = true
#endif
    >
    static void setStaticField(const char *field, T &&value)
    {
        QJniObject::setStaticField<Class, T>(field, std::forward<T>(value));
    }
 
    // keep only these overloads, the rest is made private
    template <typename Ret, typename ...Args
#ifndef Q_QDOC
        , QtJniTypes::IfValidSignatureTypes<Ret, Args...> = true
#endif
    >
    auto callMethod(const char *method, Args &&...args) const
    {
        return m_object.callMethod<Ret>(method, std::forward<Args>(args)...);
    }
    template <typename T
#ifndef Q_QDOC
        , QtJniTypes::IfValidFieldType<T> = true
#endif
    >
    auto getField(const char *fieldName) const
    {
        return m_object.getField<T>(fieldName);
    }
 
    template <typename T
#ifndef Q_QDOC
        , QtJniTypes::IfValidFieldType<T> = true
#endif
    >
    void setField(const char *fieldName, T &&value)
    {
        m_object.setField(fieldName, std::forward<T>(value));
    }
 
    QByteArray className() const {
        return QtJniTypes::Traits<Class>::className().data();
    }
 
private:
    friend bool comparesEqual(const JObject &lhs, const JObject &rhs) noexcept
    { return lhs.m_object == rhs.m_object; }
    Q_DECLARE_EQUALITY_COMPARABLE_LITERAL_TYPE(JObject);
};
}
 
// This cannot be included earlier as QJniArray is a QJniObject subclass, but it
// must be included so that we can implement QJniObject::LocalFrame conversion.
QT_END_NAMESPACE
#include <QtCore/qjniarray.h>
QT_BEGIN_NAMESPACE
 
template <typename ...Args>
template <typename T>
auto QJniObject::LocalFrame<Args...>::convertToJni(T &&value)
{
    using Type = q20::remove_cvref_t<T>;
    if constexpr (std::is_same_v<Type, QString>) {
        return newLocalRef<jstring>(QJniObject::fromString(value));
    } else if constexpr (QtJniTypes::IsJniArray<Type>::value) {
        return value.arrayObject();
    } else if constexpr (QJniArrayBase::canConvert<T>) {
        using QJniArrayType = decltype(QJniArrayBase::fromContainer(std::forward<T>(value)));
        using ArrayType = decltype(std::declval<QJniArrayType>().arrayObject());
        return newLocalRef<ArrayType>(QJniArrayBase::fromContainer(std::forward<T>(value)).template object<jobject>());
    } else if constexpr (std::is_base_of_v<QJniObject, Type>
                      || std::is_base_of_v<QtJniTypes::JObjectBase, Type>) {
        return value.object();
    } else {
        return std::forward<T>(value);
    }
}
 
template <typename ...Args>
template <typename T>
auto QJniObject::LocalFrame<Args...>::convertFromJni(QJniObject &&object)
{
    using Type = q20::remove_cvref_t<T>;
    if constexpr (std::is_same_v<Type, QString>) {
        return object.toString();
    } else if constexpr (QtJniTypes::IsJniArray<Type>::value) {
        return T(std::move(object));
    } else if constexpr (QJniArrayBase::canConvert<Type>) {
        // if we were to create a QJniArray from Type...
        using QJniArrayType = decltype(QJniArrayBase::fromContainer(std::declval<Type>()));
        // then that QJniArray would have elements of type
        using ElementType = typename QJniArrayType::Type;
        // construct a QJniArray from a jobject pointer of that type
        return QJniArray<ElementType>(object.template object<jarray>()).toContainer();
    } else if constexpr (std::is_array_v<Type>) {
        using ElementType = std::remove_extent_t<Type>;
        return QJniArray<ElementType>(std::move(object));
    } else if constexpr (std::is_base_of_v<QJniObject, Type>
                        && !std::is_same_v<QJniObject, Type>) {
        return T{std::move(object)};
    } else if constexpr (std::is_base_of_v<QtJniTypes::JObjectBase, Type>) {
        return T{std::move(object)};
    } else {
        return std::move(object);
    }
}
 
 
QT_END_NAMESPACE
 
#endif
 
#endif // QJNIOBJECT_H