c++ - Qt/C++将通用对象序列化为QSettings

我的应用程序中有几次要在其中将复合对象保存到QSettings中的事件:

template <typename T>
class AwsProperty
{
public:
    AwsProperty(T value, quint64 timestamp){
        m_data = value;
        m_timestamp = timestamp;
    }
    AwsProperty(){}
    T value(){return m_data;}
    void update(T value,quint64 timestamp){m_data = value; m_timestamp = timestamp;}
    quint64 timestamp(){return m_timestamp;}

    void toQDataStream(QDataStream &dstream){dstream << m_data << m_timestamp;}
    void fromQDataStream(QDataStream &dstream){dstream >> m_data >> m_timestamp;}
private:
    quint64 m_timestamp;
    T m_data;
};

typedef AwsProperty<qint32> AwsPropertyInt32;
Q_DECLARE_METATYPE(AwsPropertyInt32)
typedef AwsProperty<quint32> AwsPropertyUint32;
Q_DECLARE_METATYPE(AwsPropertyUint32)
typedef AwsProperty<bool> AwsPropertyBool;
Q_DECLARE_METATYPE(AwsPropertyBool)

cpp看起来像这样:

template <typename T>
QDataStream& operator<<(QDataStream& out, const AwsProperty<T>& classObj){
{
    classObj.toQDataStream(out);
    return out;
}
template <typename T>
QDataStream& operator>>(QDataStream& in, const AwsProperty<T>& classObj){
    classObj.fromQDataStream(in);
    return in;
}

我在主目录中注册了它们:

  qRegisterMetaTypeStreamOperators<AwsPropertyInt32>("AwsPropertyInt32");
    qRegisterMetaTypeStreamOperators<AwsPropertyUint32>("AwsPropertyUint32");
    qRegisterMetaTypeStreamOperators<AwsPropertyBool>("AwsPropertyBool");

我得到的错误是:

/opt/XXXXXXXXXX/0.9.99/sysroots/cortexa9hf-neon-XXXXXX-linux-gnueabi/usr/include/QtCore/qmetatype.h:810: error: no match for ‘operator<<’ (operand types are ‘QDataStream’ and ‘const AwsProperty<int>’)
         stream << *static_cast<const T*>(t);
         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~

还有为什么未为QDataStream和QString定义流运算符。

最佳答案

在实例化qRegisterMetaTypeStreamOperators之前，必须使用 QSettings 将操作符注册到元类型系统。

同样，运算符的常量性以及fromQDataStream和toQDataStream方法也有一些错误(请参阅链接以获取所需的确切原型(prototype))。

编辑:

该代码对我有用:请注意，由于它们是模板，因此我更改了某些方法的常量并将操作符移至头文件。

awsproperty.h

#include <QDataStream>

template <typename T>
class AwsProperty
{
public:
    AwsProperty(T value, quint64 timestamp){
        m_data = value;
        m_timestamp = timestamp;
    }
    AwsProperty(){}
    T value(){return m_data;}
    void update(T value,quint64 timestamp){m_data = value; m_timestamp = timestamp;}
    quint64 timestamp(){return m_timestamp;}

    void toQDataStream(QDataStream &dstream) const {dstream << m_data << m_timestamp;}
    void fromQDataStream(QDataStream &dstream){dstream >> m_data >> m_timestamp;}
private:
    quint64 m_timestamp;
    T m_data;
};

template <typename T>
QDataStream& operator<<(QDataStream& out, const AwsProperty<T>& classObj) {
    classObj.toQDataStream(out);
    return out;
}

template <typename T>
QDataStream& operator>>(QDataStream& in, AwsProperty<T>& classObj) {
    classObj.fromQDataStream(in);
    return in;
}

typedef AwsProperty<qint32> AwsPropertyInt32;
Q_DECLARE_METATYPE(AwsPropertyInt32)
typedef AwsProperty<quint32> AwsPropertyUint32;
Q_DECLARE_METATYPE(AwsPropertyUint32)
typedef AwsProperty<bool> AwsPropertyBool;
Q_DECLARE_METATYPE(AwsPropertyBool)

main.cpp

#include "awsproperty.h"
#include <QSettings>
#include <QDebug>

int main(int argc, char *argv[])
{
    qRegisterMetaTypeStreamOperators<AwsPropertyInt32>("AwsPropertyInt32");
    qRegisterMetaTypeStreamOperators<AwsPropertyUint32>("AwsPropertyUint32");
    qRegisterMetaTypeStreamOperators<AwsPropertyBool>("AwsPropertyBool");
    QSettings set("/tmp/testsettings.conf");

    AwsPropertyInt32 a{-2, 100};
    set.setValue("property", QVariant::fromValue(a));
    auto val = set.value("property").value<AwsPropertyInt32>();
    qDebug() << val.value() << " " << val.timestamp();
}

关于c++ - Qt/C++将通用对象序列化为QSettings，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/60816176/