Unexpected binding in QML with Q_GADGET - qt

Question

I have a gadget:
class ZScoreParams
{
Q_GADGET
Q_PROPERTY(quint64 lag MEMBER lag);
Q_PROPERTY(qreal threshold MEMBER threshold);
Q_PROPERTY(qreal influence MEMBER influence);
public:
std::size_t lag;
double threshold;
double influence;
};
Q_DECLARE_METATYPE(ZScoreParams)
and a property of an object of type QVariant:
Q_PROPERTY(QVariant zscoreParams READ zscoreParams WRITE setZscoreParams NOTIFY zscoreParamsChanged)
its getter returns either QVariant{} that is null in QML or QVariant::fromValue(gadget_val), the setter has the same logic.
Can't figure out how do I create a dialog with three SpinBox-es for editing my ZScoreParams. What is the right way to create it?
I attempted this ZParamsEdit.qml:
GridLayout
{
property var params
property var refreshChart: function () {}
signal zparamsChanged()
Component.onCompleted:
{
refreshChart = function ()
{
params.lag = lagEdit.value
params.threshold = thresholdEdit.value
params.influence = influenceEdit.realValue
logTable.debug("qml", JSON.stringify(params))
zparamsChanged()
}
}
Layout.margins: 5
columns: 2
flow: GridLayout.LeftToRight
Label {
text: qsTr("Lag:")
Layout.alignment: Qt.AlignRight
}
SpinBox {
id: lagEdit
value: params.lag
from: 100
to: 1000000
stepSize: 100
editable: true
Layout.alignment: Qt.AlignLeft
onValueChanged: refreshChart()
}
Label {
text: qsTr("Threshold:")
Layout.alignment: Qt.AlignRight
}
SpinBox {
id: thresholdEdit
value: params.threshold
from: 0
to: 100
stepSize: 1
editable: true
Layout.alignment: Qt.AlignLeft
onValueChanged: refreshChart()
}
Label {
text: qsTr("Influence:")
Layout.alignment: Qt.AlignRight
}
RealEdit
{
Layout.alignment: Qt.AlignLeft
id: influenceEdit
decimals: 2
realValue: params.influence
realFrom: 0
realTo: 1.0
realStepSize: 0.1
onValueChanged: refreshChart()
}
}
and then in main.qml:
Dialog
{
id: zdlg
ZParamsEdit
{
id: zedit
}
}
IconButton {
icon.source: "images/analyze.svg"
onClicked: {
zedit.params = market.zscoreParams
zdlg.open()
}
}
and got an effect that I did not expect. Each time an edit box changes, market.zscoreParams property setter is called.
How to make ZParamsEdit store a copy of my gadget and set my property value only once (with the gadget as a whole) when 'OK' button is pressed in the dialog?
Also tried
JSON.parse(JSON.stringify(market.zscoreParams))
but got also something unexpected.
EDIT1:
I probably found an ugly solution with an explicitly defined function that creates a copy of the gadget:
Q_INVOKABLE QVariant cloneZScoreParams(QVariant v)
{
std::optional<ZScoreParams> val;
util::FromVariant(v, val);
return util::ToVariant(val);
}
and then
globalSettings.cloneZScoreParams(market.zscoreParams)
in QML.
Is there something better in QT?

Answer 1

If I understand your problem correctly, you just need some sort of local property/properties to store the copy of your data, and then you need some function that writes those copies back to data source.
Here's how I would change your code:
GridLayout
{
property var params
// Copy the data into local properties
property lag: params.lag
property threshold: params.threshold
property influence: params.influence
// Only update the local properties when spinboxes change
function refreshChart()
{
lag = lagEdit.value
threshold = thresholdEdit.value
influence = influenceEdit.realValue
zparamsChanged()
}
// Call this when OK button is clicked
function save()
{
params.lag = lag
params.threshold = threshold
params.influence = influence
}
signal zparamsChanged()
...
SpinBox {
id: lagEdit
value: lag
...
onValueChanged: refreshChart()
}
SpinBox {
id: thresholdEdit
value: threshold
...
onValueChanged: refreshChart()
}
RealEdit
{
id: influenceEdit
realValue: influence
...
onValueChanged: refreshChart()
}
}
UPDATE:
To avoid calling setter 3 times, you can provide an invokable function in your C++ class:
Q_INVOKABLE void save(quint64 l, qreal t, qreal i)
{
lag = l;
threshold = t;
influence = i;
}
Now the save() function would look like this:
function save()
{
params.save(lag, threshold, influence)
}