【发布时间】：2013-05-14 17:29:03
【问题描述】：
我在从 QSetting 读取自定义元类型数据时遇到问题。 我有一堂课：
class MusicOwner
{
public:
MusicOwner() :
songs_count(0),
id(0)
{}
explicit MusicOwner(const Song &owner_radio);
Song toOwnerRadio() const;
static QList<MusicOwner> parseMusicOwnerList(const QVariant &request_result);
private:
friend QDataStream &operator <<(QDataStream &stream, const VkService::MusicOwner &val);
friend QDataStream &operator >>(QDataStream &stream, VkService::MusicOwner &val);
friend QDebug operator<< (QDebug d, const MusicOwner &owner);
int songs_count;
int id;
QString name;
QString screen_name;
QUrl photo;
};
Q_DECLARE_METATYPE(VkService::MusicOwner)
重载：
QDataStream &operator <<(QDataStream &stream, const VkService::MusicOwner &val)
{
stream << val.id;
stream << val.name;
stream << val.songs_count;
stream << val.screen_name;
return stream;
}
QDataStream &operator >>(QDataStream &stream, VkService::MusicOwner &val)
{
stream >> val.id;
stream >> val.name;
stream >> val.songs_count;
stream >> val.screen_name;
return stream;
}
QDebug operator <<(QDebug d, const VkService::MusicOwner &owner)
{
d << "MusicOwner("
<< owner.id << ","
<< owner.name << ","
<< owner.songs_count << ","
<< owner.screen_name << ")";
return d;
}
我在程序开始的某个地方调用：
qRegisterMetaTypeStreamOperators<MusicOwner>("MusicOwner");
为了读写，我使用了两个函数： 保存工作正常，我保存的所有数据都显示在设置文件中。
void VkService::SaveBookmarks()
{
TRACE;
QSettings s;
s.beginGroup(kSettingGroup);
s.beginWriteArray("bookmarks");
int index = 0;
for (int i = 0; i < root_item_->rowCount(); ++i){
auto item = root_item_->child(i);
if (item->data(InternetModel::Role_Type).toInt() == Type_Bookmark){
Song song = item->data(InternetModel::Role_SongMetadata).value<Song>();
s.setArrayIndex(index);
MusicOwner owner(song);
qLog(Info) << "Save" << index << ":" << owner;
s.setValue("owner", QVariant::fromValue(owner));
++index;
}
}
s.endArray();
}
这个函数的问题，它的加载计数正确，但它加载的是空的默认构造项。
void VkService::LoadBookmarks()
{
QSettings s;
s.beginGroup(kSettingGroup);
int max = s.beginReadArray("bookmarks");
for (int i = 0; i < max; ++i){
s.setArrayIndex(i);
MusicOwner owner = s.value("owner").value<MusicOwner>();
qLog(Info) << "Load" << i << ":" << owner;
AppendBookmarkFromRadio(root_item_, owner.toOwnerRadio());
}
s.endArray();
}
我将它重写到新项目进行测试，但它工作正常。 我花了两个小时来找出为什么这个变体能正确读取数据但第一个变体不能。 第一个变体的所有者正确转换。甚至两种变体的设置文件中的数据都相同。
#include <QCoreApplication>
#include <QDataStream>
#include <QDebug>
#include <QUrl>
#include <QSettings>
#include <QVariant>
class MusicOwner
{
public:
MusicOwner() :
songs_count(0),
id(0)
{}
private:
friend QDataStream &operator <<(QDataStream &stream, const MusicOwner &val);
friend QDataStream &operator >>(QDataStream &stream, MusicOwner &val);
friend QDebug operator<< (QDebug d, const MusicOwner &owner);
public:
int songs_count;
int id;
QString name;
QString screen_name;
QUrl photo;
};
QDataStream &operator <<(QDataStream &stream, const MusicOwner &val)
{
stream << val.id;
stream << val.name;
stream << val.songs_count;
stream << val.screen_name;
return stream;
}
QDataStream &operator >>(QDataStream &stream, MusicOwner &val)
{
stream >> val.id;
stream >> val.name;
stream >> val.songs_count;
stream >> val.screen_name;
return stream;
}
QDebug operator <<(QDebug d, const MusicOwner &owner)
{
d << "MusicOwner("
<< owner.id << ","
<< owner.name << ","
<< owner.songs_count << ","
<< owner.screen_name << ")";
return d;
}
Q_DECLARE_METATYPE(MusicOwner)
const QString kSettingGroup = "Group";
void Save() {
QSettings s;
s.beginGroup(kSettingGroup);
s.beginWriteArray("bookmarks");
int index = 0;
for (int i = 0; i < 100; ++i){
if (random() % 5 == 0) {
s.setArrayIndex(index);
MusicOwner owner;
owner.id = i;
owner.name ="Hello world";
owner.songs_count = i * 2;
owner.screen_name = "hello_world";
s.setValue("owner", QVariant::fromValue(owner));
qDebug() << "Saved" << i << ":" << owner;
++index;
}
}
s.endArray();
qDebug() << "Saved" << index << "elements";
}
void Load() {
QSettings s;
s.beginGroup(kSettingGroup);
int max = s.beginReadArray("bookmarks");
qDebug() << "To load" << max << "elements";
for (int i = 0; i < max; ++i){
s.setArrayIndex(i);
MusicOwner owner = s.value("owner").value<MusicOwner>();
qDebug() << "\tLoaded" << i << ":" << owner;
}
s.endArray();
}
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
qRegisterMetaTypeStreamOperators<MusicOwner>("MusicOwner");
QSettings s;
Load();
Save();
return a.exec();
}
也许您会发现在此变体中使用 QSettings 的不同之处？
【问题讨论】：