c++ - 将 C++ 自定义类型公开给 QML

Question

我有以下 C++ 自定义对象，希望在 QML 中用作 enum 类型:

#include <QtQml>
#include <QApplication>
#include <QQmlApplicationEngine>

#include "database/uepeoplemodel.h"
#include "core/uestatus.h"
#include "core/uedatabaseconnectionstatus.h"

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QQmlApplicationEngine engine;

    UeStatus* ueApplicationStatus=new UeStatus(qApp);
    UePeopleModel* uePeopleModel=new UePeopleModel(qApp);

    QObject::connect(uePeopleModel,
                     SIGNAL(ueSignalDatabaseConnectionChanged(UeDatabaseConnectionStatus::UeTypeDatabaseConnectionStatus)),
                     ueApplicationStatus,
                     SLOT(ueSignalDatabaseConnectionChanged(UeDatabaseConnectionStatus::UeTypeDatabaseConnectionStatus)));

    uePeopleModel->ueConnectToDatabase();

    engine.rootContext()->setContextProperty("uePeopleModel",
                                             uePeopleModel);
    engine.rootContext()->setContextProperty("ueApplicationStatus",
                                             ueApplicationStatus);
    engine.addImageProvider(QLatin1String("uePeopleModel"),
                            uePeopleModel);

    qmlRegisterUncreatableType<UeDatabaseConnectionStatus::UeTypeDatabaseConnectionStatus>("si.mikroelektronika",
                                                                                           1,
                                                                                           0,
                                                                                           "UeTypeDatabaseConnectionStatus",
                                                                                           "Database Connection Status");

    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

    return app.exec();
}

我收到以下编译错误(在 Linux work002 3.19.0-28-generic#30-Ubuntu SMP Mon Aug 31 15:52:51 UTC 2015 上使用 gcc version 4.9.2 x86_64 x86_64 x86_64 GNU/Linux:

In file included from /opt/QtOpenSource55/5.5/gcc_64/include/QtCore/qobject.h:40:0, from /opt/QtOpenSource55/5.5/gcc_64/include/QtCore/qabstractanimation.h:37, from /opt/QtOpenSource55/5.5/gcc_64/include/QtCore/QtCore:4, from /opt/QtOpenSource55/5.5/gcc_64/include/QtQml/QtQmlDepends:3, from /opt/QtOpenSource55/5.5/gcc_64/include/QtQml/QtQml:3, from ../ueBlagajnaClient/main.cpp:1: /opt/QtOpenSource55/5.5/gcc_64/include/QtCore/qobjectdefs.h:88:5: error: class definition may not be declared a friend friend Q_DECL_CONSTEXPR const QMetaObject *qt_getEnumMetaObject(ENUM) Q_DECL_NOEXCEPT { return &staticMetaObject; } \ ^ ../ueBlagajnaClient/database/../core/uedatabaseconnectionstatus.h:17:5: note: in expansion of macro 'Q_ENUM' Q_ENUM(UeTypeDatabaseConnectionStatus) ^ /opt/QtOpenSource55/5.5/gcc_64/include/QtCore/qobjectdefs.h:88:35: error: 'QMetaObject' is neither function nor member function; cannot be declared friend friend Q_DECL_CONSTEXPR const QMetaObject *qt_getEnumMetaObject(ENUM) Q_DECL_NOEXCEPT { return &staticMetaObject; } \ ^ ../ueBlagajnaClient/database/../core/uedatabaseconnectionstatus.h:17:5: note: in expansion of macro 'Q_ENUM' Q_ENUM(UeTypeDatabaseConnectionStatus) ^ /opt/QtOpenSource55/5.5/gcc_64/include/QtCore/qobjectdefs.h:88:35: error: expected ';' at end of member declaration friend Q_DECL_CONSTEXPR const QMetaObject *qt_getEnumMetaObject(ENUM) Q_DECL_NOEXCEPT { return &staticMetaObject; } \ ^ ../ueBlagajnaClient/database/../core/uedatabaseconnectionstatus.h:17:5: note: in expansion of macro 'Q_ENUM' Q_ENUM(UeTypeDatabaseConnectionStatus) ^ /opt/QtOpenSource55/5.5/gcc_64/include/QtCore/qobjectdefs.h:88:73: error: ISO C++ forbids declaration of 'qt_getEnumMetaObject' with no type [-fpermissive] friend Q_DECL_CONSTEXPR const QMetaObject qt_getEnumMetaObject(ENUM) Q_DECL_NOEXCEPT { return &staticMetaObject; } \ ^ ../ueBlagajnaClient/database/../core/uedatabaseconnectionstatus.h:17:5: note: in expansion of macro 'Q_ENUM' Q_ENUM(UeTypeDatabaseConnectionStatus) ^ ../ueBlagajnaClient/database/../core/uedatabaseconnectionstatus.h: In member function 'int UeDatabaseConnectionStatus::qt_getEnumMetaObject(UeDatabaseConnectionStatus::UeTypeDatabaseConnectionStatus)': /opt/QtOpenSource55/5.5/gcc_64/include/QtCore/qobjectdefs.h:88:101: error: cannot convert 'const QMetaObject*' to 'int*' in return friend Q_DECL_CONSTEXPR const QMetaObject qt_getEnumMetaObject(ENUM) Q_DECL_NOEXCEPT { return &staticMetaObject; } \ ^ ../ueBlagajnaClient/database/../core/uedatabaseconnectionstatus.h:17:5: note: in expansion of macro 'Q_ENUM' Q_ENUM(UeTypeDatabaseConnectionStatus) ^ In file included from /opt/QtOpenSource55/5.5/gcc_64/include/QtQml/QtQml:9:0, from ../ueBlagajnaClient/main.cpp:1: /opt/QtOpenSource55/5.5/gcc_64/include/QtQml/qqml.h: In instantiation of 'int qmlRegisterUncreatableType(const char, int, int, const char*, const QString&) [with T = UeDatabaseConnectionStatus::UeTypeDatabaseConnectionStatus]': ../ueBlagajnaClient/main.cpp:35:120: required from here /opt/QtOpenSource55/5.5/gcc_64/include/QtQml/qqml.h:83:59: error: 'staticMetaObject' is not a member of 'UeDatabaseConnectionStatus::UeTypeDatabaseConnectionStatus' const char *className = T::staticMetaObject.className(); \ ^ /opt/QtOpenSource55/5.5/gcc_64/include/QtQml/qqml.h:134:5: note: in expansion of macro 'QML_GETTYPENAMES' QML_GETTYPENAMES ^ In file included from /opt/QtOpenSource55/5.5/gcc_64/include/QtQml/QtQml:9:0, from ../ueBlagajnaClient/main.cpp:1: /opt/QtOpenSource55/5.5/gcc_64/include/QtQml/qqml.h:144:51: error: 'staticMetaObject' is not a member of 'UeDatabaseConnectionStatus::UeTypeDatabaseConnectionStatus' uri, versionMajor, versionMinor, qmlName, &T::staticMetaObject, ^ Makefile:1319: recipe for target 'main.o' failed make: *** [main.o] Error 1 08:04:15: The process "/usr/bin/make" exited with code 2. Error while building/deploying project ueBlagajnaClient (kit: Desktop Qt 5.5.0 GCC 64bit) When executing step "Make"

为什么以及如何摆脱这个错误？我如何滥用方法 qmlRegisterUncreatableType？

Answer 1

如果要使用qmlRegisterType，使用的类必须是继承QObject并且有Q_OBJECT宏的类:

class UeTypeDatabaseConnectionStatus: public QObject
{
    Q_OBJECT

public:
    enum StatusEnum
    {
        NOT_CONNECTED=false,
        CONNECTED=true
    }
    Q_ENUM(StatusEnum)
    ...
}

在 QML 中，您可以创建它的一个实例，就像您创建任何其他 QML 类一样。

编辑:但是，由于您只想使用枚举值，因此请改用 qmlRegisterUncreatableType。通过这种方式注册类型，但您无法创建它的实例。

要访问枚举值，导入类型并像使用任何其他枚举一样使用它:

connectionProperty: UeTypeDatabaseConnectionStatus.CONNECTED;