Call base object method from QML

St.Stanislav

Hello all! I have the following situation: I use FileDialog from Qt.labs.platform 1.1 and pass FileDialog.file to C++ QObject. Before I have used one object with methods and everything works well (QML calls method with QUrl argument which, in turn, calls QString case)

Q_INVOKABLE void saveToFile(QUrl url) {saveToFile(url.toLocalFile())};
Q_INVOKABLE void saveToFile(QString string){//some processing};

Now I have base class with common method and virtual abstract one

Q_INVOKABLE void saveToFile(QUrl url) {saveToFile(url.toLocalFile())};
Q_INVOKABLE virtual void saveToFile(QString string) = 0;

So in the derived class I have different definitions of the method void saveToFile(QString string). Following this idea, I try to call saveToFile from QML for the derived objects. But the override method is calling with converting (QML url to Qstring directly). How can I avoid this situation and call base method from QML? Of course I can give different names, but I'm interested in common case and, maybe, good practices.

sierdzio

In order to call the QUrl overload, you need to pass a url variable instead of string. Here is - somewhat hacky - solution:

FileDialog {
property url myUrl: file
}
// JS
yourCppObject.saveToFile(myUrl)

Not tested - I hope it will work though :P If not, then different method names is the right solution.

St.Stanislav

@sierdzio Hello and thank you for the fast reply! Looks like it failed to be workaround :) Moreover, it says in documentation that FileDialog.file is already url type. So looks like there is no difference for passing this argument.

One more thing that I have tried and it works: redefine the method in the derived class with QUrl argument and call parent method directly:

void Derived::saveToFile(QUrl filename) {
    Base::saveToFile(filename);
}

This workaround works and seems to be ok in my case.

sierdzio

Interesting! OK, nice that you've found a solution :-)

KroMignon

@St-Stanislav said in Call base object method from QML:

void Derived::saveToFile(QUrl filename) {
Parent::saveToFile(filename);
}

This is a C++ 'issue', you have to tell C++ compiler you want to keep previous definition:

class BaseClass : public QObject
{
    Q_OBJECT
public:
    Q_INVOKABLE void saveToFile(QString string){//some processing};;
}

class DerivedClass : public BaseClass
{
    Q_OBJECT
 
public:
    using BaseClass::saveToFile;
    Q_INVOKABLE void saveToFile(QUrl url) {saveToFile(url.toLocalFile()); };
}

==> http://www.cs.technion.ac.il/users/yechiel/c++-faq/hiding-rule.html

St.Stanislav

@KroMignon Yes, I have caught it and solved it in the same way, but I wondered if it's any chance to call base class method from QML directly :)

KroMignon

@St-Stanislav said in Call base object method from QML:

if it's any chance to call base class method from QML directly :)

What do you mean?

myCppClass.saveToFile("TEST"); // => should call saveToFile(QString) 
myCppClass.saveToFile(Qt.resolvedUrl("test.qml")); // => should call saveToFile(QUrl)

St.Stanislav

@KroMignon Well, looks like your solution is also not for me (cause of several methods with one name I have used the second solution from the link you posted). I get why this methods are called, get what solution I can use, but I was wondering if this problem can be solved from QML side :)
I have created tiny example project, but have no idea how to post it here correctly.

KH-219Design

I'm not sure if I understand things with total clarity.

However, if I understand, then these both exist in a base class:

/* (1) */ Q_INVOKABLE void saveToFile(QUrl url) {saveToFile(url.toLocalFile())};
/* (2) */ Q_INVOKABLE virtual void saveToFile(QString string) = 0;

And some QML code is triggering entry/execution into (2) instead of (1).

In that case, I wonder why not just remove Q_INVOKABLE from (2) so that it is not-invokable from QML?