Is it possible to create binding proxy in qt qml? - qt

Question

i have a cpp struct which have so much fields
struct CloudMusicSongList{ ... };
and i want use it in qml in order input some infomation to it's instance, but i don't want to create a qobject derived class,and create a lot of qproperty ...
i seache in google and get this code snippt from this blog
class ListItem : public QObject
{
Q_OBJECT
public :
ListItem(QObject *parent = 0) : QObject(parent) {}
virtual ~ListItem() {}
virtual int id() const = 0;
virtual QVariant data(int role) const = 0;
virtual QHash<int, QByteArray> roleNames() const = 0;
virtual void triggerItemUpdate() {emit dataChanged();}
signals:
void dataChanged();
};
i just try following code but even not print called data method
defined.h
template <typename T>
class bindingProxy : public bindingProxyBase
{
public:
bindingProxy(QObject* parent = 0)
: bindingProxyBase(parent)
{
}
T tm;
virtual ~bindingProxy()
{
}
virtual QVariant data(int role)
{
qDebug() << "called data method";
QVariant qv;
auto fucs = Prism::Reflection::get_md<T>();
if (role == Qt::DisplayRole)
fucs[0].getFunc(tm, 0, qv);
else
fucs[role].getFunc(tm, role, qv);
return qv;
}
QHash<int, QByteArray> roleNames() const
{
static QHash<int, QByteArray> roles{};
if (roles.count() == 0)
{
for (Prism::Reflection::PrismMetaData<T>& item : Prism::Reflection::get_md<T>())
{
roles[item.offset] = item.name;
}
}
return roles;
}
bool setData(QVariant& value, int role = Qt::EditRole)
{
Prism::Reflection::get_md<T>()[role].setFunc(tm, role, value);
triggerItemUpdate();
return true;
}
};
bodyViewModel.cpp
#include ....
...
..
Q_DECLARE_METATYPE(bindingProxy<CloudMusicSongList>*);
class BodyViewModel : public QObject
{
Q_PROPERTY(bindingProxy<CloudMusicSongList>* editSongListModel READ editSongListModel WRITE setEditSongListModel NOTIFY editSongListModelChanged)
...
...
...
uing.qml
Button {
id:btn_tst
text: BodyViewModelCpp.editSongListModel.name + "hbb"
onClicked: BodyViewModelCpp.editSongListModel.name = "3232"
}
button look like this image after run app rung
i don't know whether it is the X Y problem.
somebody can help? thanks
i want create a bindingProxy template class which twoway bindable in qml
i think it should equivalence dynamicObject in wpf

Answer 1

Based on CloudMusicSongList I'm assuming the thing that you have is a list/array. There are quite a number of ways of exposing this to QML.
QQmlListProperty - https://doc.qt.io/qt-6/qqmllistproperty.html
QAbstractListModel - https://doc-snapshots.qt.io/qt6-dev/qabstractlistmodel.html
QVariant, QVariantList, and/or QVariantMap - https://doc-snapshots.qt.io/qt6-dev/qvariant.html
QObject / Q_OBJECT - create a new QML component and register it
Q_GADGET - register your C++ structure (good for access the class in a signal, but, QML/JS cannot copying it into a Javascript object, only good for the duration of the signal)
QQmlListProperty is a list of QObjects. It requires the underlying QObject be registered, but, allows you to create/manage and walk through a list of the results. The list is owned, usually by another QObject. e.g. we could have a QmlFile object, then implement a QmlFileSystem object that can return a list of QmlFiles.
QAbstactListModel can be used in places where a model is required, e.g. ListView.
QVariant, QVariantList and QVariantMap is the simplest way of creating a Javascript object in QML. The advantage is you do not have to register anything, but, the disadvantage is you do not get intellisense.
QVariant getBooks() {
QVariantList books;
QVariantMap book1;
book1["title"] = QString("Lord of the Rings");
QVariantMap book2;
book2["title"] = QString("The Hobbit");
books.append(book2);
return books;
// results in QML/JS:
// [ { "title": "Lord of the Rings" },
// { "title" : "The Hobbit" } ]
}