Changing the model does not redraw objects in QML sometimes - c++

Question

Repeater {
model: myModel.buttonParameters
delegate: Button
{
width: 47
height: 47
contentItem: Text {
id: content
text: modelData.name
font.family: MyStyle.fontFamily
fontSizeMode: Text.Fit
font.pixelSize: 30
font.styleName: "Bold"
topPadding: height / 6
color: modelData.visibility ? MyStyle.colorFromSeriesName(this.text) : MyStyle.dividerColor
horizontalAlignment: Text.AlignHCenter
verticalAlignment: Text.AlignVCenter
}
background: Rectangle
{
anchors.fill: parent
radius: 4
color: MyStyle.backgroundColor
border.color:MyStyle.dividerColor
border.width: 2
}
onClicked: {
cntModel.visibilityOfChartChanged(modelData.name, "plot");
}
}
}
On the C++ side.
myModel.buttonParameters is a QList<MyModel*> , where MyModel is a class inherited from QObject.
Q_PROPERTY(QVariant buttonParameters READ buttonParametersList NOTIFY buttonParametersChanged)
QVariant buttonParametersList()
{
return QVariant::fromValue(m_buttonParametersList );
}
The problem is that with a certain change in the model
(the signal buttonParametersChanged is sent), namely,
if the number of objects was equal to one and after the update there
is also one object, but with different characteristics, no redrawing
takes place, the old button remains. Moreover, it somehow depends on
the runtime. Also, if I remove the line with color, the model will update.

Answer 1

The issue is that buttonParametersChanged is a signal that triggers on the assignment of a new container (QList<>) to buttonParameters. It doesn't trigger on changes to the contents of an existing QList<> assigned to that property.
However, you can always manually trigger buttonParametersChanged when you know you've modified the contents of the QList<> which should give you the effect you want.
Note, a QML ListModel or C++ equivalent would likely be more appropriate for this use case. Many QML components are designed to specifically integrate with them and handle the cases of container contents changing.