[Solved] QObject::setProperty does not fire the appropriate signal

MichelS

Hey guys,

I've defined a property like this:

@
Q_PROPERTY(int keepAliveInterval READ keepAliveInterval WRITE setKeepAliveInterval NOTIFY keepAliveIntervalChanged)
@

And now I set the property using the QObject::setProperty -Method as described here http://qt-project.org/doc/qt-5.0/qtcore/qobject.html#setProperty

But that does not seem to fire the keepAliveIntervalChanged signal as I'd expect.

How can I fire that signal?

Background:
What I'm trying to achieve is this:
Read a JSON-file with property settings, convert that to an QVariantMap, for each item:
apply that value to the property and fire the signal.

This works so far, but no signal is fired....
@
QVariantMap::const_iterator iter;
for (iter = variants.constBegin(); iter != variants.constEnd(); ++iter) {
int pIdx = metaobject->indexOfProperty( iter.key().toLatin1() );

if ( pIdx < 0 ) {
continue;
}
object->setProperty(iter.key().toLatin1(), iter.value());
}
@

SGaist

Hi,

Qt can't know when to trigger the signal (it's your business logic).

Your setter can be something like:

@
void MyClass::setKeepAliveInterval(int interval)
{
if (_interval != interval) {
_interval = interval;
// do the needed stuff
emit keepAliveIntervalChanged(_interval)
}
}
@

raven-worx

did you specify the signal in your class definition?
what did the connect statement return?

dbzhang800

Hi, you have mis-understanded the usage and function of Q_PROPERTY.

It won't fire signal for you automatically, you must emit the signal (keepAliveIntervalChanged) manually in you set function (setKeepAliveInterval).

MichelS

Oh yes I forgot about that. You are right 1+1=2 and SGaist
Of course my setter fires the signal if it's called.
But the setter does not seem to be called.

and to raven-worx:
Yes, the connection is OK, cause I used the compiler checked connection style

@
connect(systemConfig(), &SystemConfiguration::keepAliveIntervalChanged, NetworkService::instance(), &NetworkService::setKeepAliveInterval);
@

raven-worx

please make sure that iter.key().toLatin1() returns "keepAliveInterval" and also that setProperty() returns true...meaning the right property is set.

MichelS

I checked the property afterwards and it's updated.

But anyway. I finally found a solution, by manually fire the signal.

@
void QObjectHelper::qvariant2qobject(const QVariantMap& variants, QObject* object)
{
const QMetaObject *metaobject = object->metaObject();

QVariantMap::const_iterator iter;
for (iter = variants.constBegin(); iter != variants.constEnd(); ++iter) {
    int pIdx = metaobject->indexOfProperty( iter.key().toLatin1() );

    if ( pIdx < 0 ) {
        continue;
    }
    QByteArray propertyName = iter.key().toLatin1();
    object->setProperty(propertyName, iter.value());

    QMetaProperty metaproperty = metaobject->property( pIdx );
    QVariant::Type type = metaproperty.type();
    QVariant v( iter.value() );
    if ( v.canConvert( type ) ) {
        v.convert( type );
        metaproperty.write( object, v );
        if (metaproperty.hasNotifySignal()) {
            QGenericArgument ga(v.typeName(),v.data());
            metaproperty.notifySignal().invoke(object, Qt::QueuedConnection, ga);
        }
    } else if (QString(QLatin1String("QVariant")).compare(QLatin1String(metaproperty.typeName())) == 0) {
        metaproperty.write( object, v );
    }

}

}
@

SGaist

Did you do the checks suggested by raven-worx ?

I am using setProperty and it all works well.

Also, if your setter follows the pattern of my previous post, the signal won't be fired when setting the same value.

MichelS

[quote author="SGaist" date="1372417858"]Did you do the checks suggested by raven-worx ?[/quote]
Yes, the result is true und the iter.key().toLatin1() returns “keepAliveInterval”

[quote author="SGaist" date="1372417858"]Also, if your setter follows the pattern of my previous post, the signal won't be fired when setting the same value.[/quote]
Wow!! That was the hint...
Sometimes the solution is just too easy.
Embarrassing....

SGaist

No biggies, this can happen to anyone (was bitten by something like this because the initial value of a member was the same as the one saved in settings so nothing happened)