I am not sure, if this is really a bug, or just the expected behaviour, but if
you use the systemmonitor dataEngine and connect to a source, the first update
is an empty QHash, the second update contains not the value itself, and the
third update contains the relevant information. Here a short extract from my
source code (it simply connects to the systemmonitor dataEngine, and after 4
data updates it disconnects again):
void Test::init()
{
connect( dataEngine("systemmonitor"), SIGNAL(sourceAdded(QString)), this,
SLOT(sourceAdded(QString)) );
}
void Test::sourceAdded( QString sSource )
{
if ( sSource == "partitions/home/usedspace" ) {
qDebug() << "Adding source" << sSource;
m_Time.start();
dataEngine("systemmonitor")->connectSource( "partitions/home/usedspace",
this, 2000 );
}
}
void Test::dataUpdated( const QString& sSource, const Plasma::DataEngine::Data
data )
{
static int i=0;
qDebug() << "Calling dataUpdated for source" << sSource << "Data:" << data
<< "Elapsed time:" << m_Time.elapsed();
if ( i++ > 2 )
dataEngine("systemmonitor")->disconnectSource(
"partitions/home/usedspace", this );
}
The output of this test plasmoid would be:
Adding source "partitions/home/usedspace"
Calling dataUpdated for source "partitions/home/usedspace" Data: QHash()
Elapsed time: 0
Calling dataUpdated for source "partitions/home/usedspace" Data:
QHash(("type", QVariant(QString, "integer") ) ) Elapsed time: 24
Calling dataUpdated for source "partitions/home/usedspace" Data:
QHash(("units", QVariant(QString, "Blocks") ) ( "type" , QVariant(QString,
"integer") ) ( "value" , QVariant(QString, "15039983") ) ( "min" ,
QVariant(QString, "0") ) ( "name" , QVariant(QString, "Used Blocks") ) (
"max" , QVariant(QString, "-") ) ) Elapsed time: 2001
Calling dataUpdated for source "partitions/home/usedspace" Data:
QHash(("units", QVariant(QString, "Blocks") ) ( "type" , QVariant(QString,
"integer") ) ( "value" , QVariant(QString, "15039967") ) ( "min" ,
QVariant(QString, "0") ) ( "name" , QVariant(QString, "Used Blocks") ) (
"max" , QVariant(QString, "-") ) ) Elapsed time: 4002
As we can see, the first dataUpdated comes with an empty QHash directly after
connecting, the second update comes after 24 milliseconds (why there is this
second update I do not know) with a QHash, wich only contains the information
of the type, and finally starting with the 3rd update I get all the information
I need (But only after 2001 milliseconds).
The background for the whole story is that I created a systemmonitor plasmoid
(called yasp-scripted on kde-look), where the sources can depend on each other
(as for example partitions/home/freespace depends on
partitions/home/usedspace, to get the total space). So I actually need to be
sure, that the first dataUpdated will deliver me "useful" data, or I need to
wait for it in my application. I do not know what the right way is, whether I
need to wait in my application, or the systemmonitor dataEngine needs to be
improved.
Related bugs in bugzilla:
https://bugs.kde.org/show_bug.cgi?id=202225
https://bugs.kde.org/show_bug.cgi?id=202880
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