Passing QList <QObject *> from C ++ to QML - c++

Question

Good evening,
We are programming a DaVinci DM8168 board with Qt5.7.1 and QtQuick2.7
we would like to pass a list of type:
QList from C ++ to QML
to be able to draw it asynchronously and above all efficiently. The list is modified by a thread on C ++.
We cannot state the update frequence of this list at all: it can be just one time per second or dozens! It depends by the target enviroment.
our solution (partially working) is the following:
On the C++ side we are using QPROPERTIES:
an extract of our code:
MyClass.h
class MyClass: public Observer
{
Q_OBJECT
Q_PROPERTY(QList<QObject*> getFailuresHistory READ getFailuresHistory NOTIFY failuresHistoryListChanged)
QList<QObject*>getFailuresHistory(){return failuresHistory_;}
signals:
void failuresHistoryListChanged();
}
then my .cpp we emit the signal every time the list changes ( not true at all: if more elements of the list changes at the same time we emit the signal only once in order to optimize the application)
emit failuresHistoryListChanged();
Then on QML "side" we do the following:
Item
{
// ... other code
//DELAGATE
Component
{
id: failuresDelegateHistory
Item
{
id: listHistoryItem
width: listHistory.width
height: 10
anchors.leftMargin: 5
Row
{
Text{
id: failureIdHistory
width: 30
text: qsTr(modelData.codeFailure) + mainSettingsHandler.emptyString
color: mainWindow.currentStyleColor.colorRed
font.pixelSize: 16
horizontalAlignment: Text.AlignHCenter
}
Text {
id: descriptionFailIdHistory
width: (listHistoryItem.width-failureIdHistory.width)*0.5
color:mainWindow.currentStyleColor.colorWhite
maximumLineCount: 1
text: qsTr(modelData.descriptionFail) + mainSettingsHandler.emptyString
wrapMode: Text.WrapAnywhere
horizontalAlignment: Text.AlignJustify
font.pixelSize: 12//16
}
Text
{
id: columnTimeStampFailureHistory
width: (listHistoryItem.width-descriptionFailIdHistory.width-failureIdHistory.width- 2)
maximumLineCount: 1
text: modelData.dateFail + mainSettingsHandler.emptyString
wrapMode: Text.WrapAnywhere
color:mainWindow.currentStyleColor.colorWhite
font.pixelSize: 12
horizontalAlignment: Text.AlignJustify
}
}
}
}
//LIST
ListView
{
id: list1
y: labelHistory.y + labelHistory.height+5
width: (FileConfiguration.widthMenuArea - space - 5)*0.5-1-space
height: (270 - space) *itemsPerPage
model: myClass.getFailuresHistory//failuresHistoryTable.getFailuresHisory
delegate: failuresDelegateHistory
spacing: 10
enabled: false
}
// ... other code
}
OK;
as I said before this solution is partially working because is very, very slow!
When the:
emit failuresHistoryListChanged();
on c++ side is called, the list is drawn but the software is "slow". We have keepalive message that shall be set every 300 ms and that is not sent anymore for a couple of seconds.
We need a more efficent way to pass the list to the QML.
if we comment the emit the software works fine within its deadlines.
So our purpose is: we would like to pass in a very efficent way this list to QML. Do you have solutions that involve a modification of the code that we have shown you or new architectures? do you have any examples? we are not experts in qml.
If you need more information ask us.
We thank you in advance, we have been trying to solve the problem for a long time.
thanks