[SOLVED] Crash of app when exchanging objects from C++ to QML
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Dear all,
I'm using Qt 5.2.1 for developing an app on iOS.
In the app there is a C++ part that provides various objects (registered with qmlRegisterType) to the QML part where the data of such objects are displayed.I'm experiencing a weird crash of the app during such object exchanging that I don't know how to debug and to solve.
On C++, I have some slot functions that are used on QML:
@
// return the list of object id to use in getTrait slot below
QStringList DatObject::getTraits() {
return orderedTraits;
}
// return an object that it is used on QML part
TraitObject *DatObject::getTrait( QString traitId ) {
if ( traits.contains(traitId) ) {
qDebug() << "GetTrait:" << traits[traitId] << " - " << traitId;
return traits[traitId];
}
// return a dummy created object (this should never happens)
// ---- This is a leaky but it will be not called
return (new TraitObject());
}
@on QML, I have a ListView for display a list of objects:
@
ListView {
id: listTraits
model: personalDat.dat.getTraits()
delegate: TraitView {
width: parent.width
Component.onCompleted: {
var trait = personalDat.dat.getTrait( modelData )
console.log( "TraitView: "+trait+" - "+modelData )
if ( trait != null ) {
traitObject = trait
isEditable = personalDat.dat.isMe()
}
}
}
}
@Into the slot getTrait and into the delegate TraitView, I put some print out to show what happens.
The QML file whit the ListView is pushed and popped from a StackView various time for showing different list of TraitObjects.
The code works well for a while (not always the same number of time), and a certain time it crash !!
The debug prints show something weird:
@
QML Side -> DAT to view: DatObject(0x17d06f20)
C++ Side -> GetTrait: TraitObject(0x17f92340) - "5367cdf7698b3c4d46010098"
QML Side -> TraitView: TraitObject(0x17f92340) - 5367cdf7698b3c4d46010098
C++ Side -> GetTrait: TraitObject(0x17f8f770) - "5367cdf8698b3c0a5a033401"
QML Side -> TraitView: TraitObject(0x17f8f770) - 5367cdf8698b3c0a5a033401
C++ Side -> GetTrait: TraitObject(0x17f8f1c0) - "5367ce0b698b3c4d460100a8"
QML Side -> TraitView: null - 5367ce0b698b3c4d460100a8
@If you note the last two rows, the debug print into the getTraits in C++ indicate that a valid TraitObject is going to be returned to the QML ... but the debug print on the QML indicate that it's arrived a "null" object !!
Why ?!?!
And as soon as this happens the app crash with a lot of messages like:
@
program received signal -111, <something-very-long-that-I-dont-understand>
hit maximum number of signal, stopping
@ -
My first guess would be that this crash is caused by Qml assuming ownership of the object returned from getTrait()
Please see "Data ownership":http://qt-project.org/doc/qt-5/qtqml-cppintegration-data.html
This is also why the comment in:
@
// ---- This is a leaky but it will be not called
return (new TraitObject());
@is incorrect. This will not leak because Qml assumes ownership and disposes the object when it is no longer referenced.
