Q_PROPERTY c++/QML

Delta_sim

Hello,

I would like to know if it's safe to use a lot of Q_PROPERTY in a qt quick application.
My database is in c++ and I have to use this database in QML (most of the time read-only).

Thanks for your help.

sierdzio

Yes it is safe. QML uses only Qt properties to achieve its functionality. Everything you set (like color: "red" in a Rectangle) is a Q_PROPERTY.

dheerendra

Your idea is to expose the values present in Database. You would like to read them & pass the values to QML. Hope this is right. As @sierdzio suggested already, you can use Q_PROPERTY. It is designed for this. You can also expose the list to QML side as Q_PROPERTY instead of individual Q_PROPERTY.

Delta_sim

Ok thanks for your replies.
@dheerendra you suggested to expose the list to QML and it's a good idea, QQmlListProperty will do the job ? Or I should use an other type ?

GrecKo

QQmlListProperty is made to expose a list so that can be populated from QML. That's not what you want.
To expose a list of data, use QAbstractListModel (read http://doc.qt.io/qt-5/qtquick-modelviewsdata-cppmodels.html#qabstractitemmodel-subclass). If your data is static, you could use simpler classes like QStringList, QVariantList (composed of QVariantMap for example) or QObjectList.

Delta_sim

Thanks @GrecKo , I will do that

Delta_sim

@GrecKo as you said I expose a QVariantList like this:

//c++
Q_PROPERTY(QList<QVariant> gav_GlobalDb READ gav_get_GlobalDb WRITE gv_set_GlobalDb)

QList<QVariant> gav_get_GlobalDb(void);
void gv_set_GlobalDb(QList<QVariant>  oav_GlobalDb);

I can read a value from QML like this:

//QML
g_GlobalDatabase.gav_GlobalDb[VAR_INDEX]

But I don't find how to write a value... I tried this but it doesn't work:

//QML
g_GlobalDatabase.gav_GlobalDb[VAR_INDEX] = true;

Can you help me this that ?

Thanks

Delta_sim

@dheerendra @sierdzio any idea please ?

sierdzio

You're assigning bool to QList<QVariant>, no wonder it does not work. I do not know how to nicely fix this.

A hacky solution would be to add a Q_INVOKABLE method with the following signature:

Q_INVOKABLE void setGlobalDb(int index, const QVariant &value);

Then from QML you could do:

g_GlobalDatabase.setGlobalDb(VAR_INDEX,  true)

Delta_sim

Thanks @sierdzio it works with Q_INVOKABLE