Can't write to a C++ object from QML - qt

Question

I have a program that displays images and can put different filters on these images. In the QML GUI I have a series of buttons that let you set which highlights are enabled.
Column{
id: highlightButtons
anchors {left: frameViewer.right; top: parent.top; leftMargin: 10; topMargin: 10 }
spacing: 20
Rectangle{
id: class1
color: "red"
height: 45
width: 45
radius: 12
MouseArea{
anchors.fill: parent
onClicked: {hl.red = frames[frameList.currentIndex];
loadImages(); console.log(hl.red)}
}
}
Rectangle{
id: class2
color: "green"
height: 45
width: 45
radius: 12
MouseArea{
anchors.fill: parent
onClicked: {hl.green = frames[frameList.currentIndex];
loadImages(); console.log(hl.green)}
}
}
Rectangle{
id: class3
color: "blue"
height: 45
width: 45
radius: 12
MouseArea{
anchors.fill: parent
onClicked: {hl.blue = frames[frameList.currentIndex];
loadImages(); console.log(hl.blue)}
}
}
}
Where frames is a list of strings.
hl is a class that I use to store which highlights are enabled.
class HighlightModel : public QObject
{
Q_PROPERTY(QString red READ getRed WRITE setRed NOTIFY redChanged)
Q_PROPERTY(QString blue READ getGreen WRITE setBlue NOTIFY blueChanged)
Q_PROPERTY(QString green READ getBlue WRITE setGreen NOTIFY greenChanged)
public:
void setRed(QString &frame)
{
if(redHighlights.find(frame) != redHighlights.end())
{
redHighlights[frame] = !redHighlights[frame];
}
else
{
redHighlights.insert(std::pair<QString, bool>(frame, true));
}
emit redChanged();
}
void setGreen(QString &frame)
{
if(greenHighlights.find(frame) != greenHighlights.end())
{
greenHighlights[frame] = !greenHighlights[frame];
}
else
{
greenHighlights.insert(std::pair<QString, bool>(frame, true));
}
emit greenChanged();
}
void setBlue(QString &frame)
{
if(blueHighlights.find(frame) != blueHighlights.end())
{
blueHighlights[frame] = !blueHighlights[frame];
}
else
{
blueHighlights.insert(std::pair<QString, bool>(frame, true));
}
emit blueChanged();
}
bool getRed(QString frame)
{
return redHighlights[frame];
}
bool getGreen(QString frame)
{
return greenHighlights[frame];
}
bool getBlue(QString frame)
{
return blueHighlights[frame];
}
std::map<QString, bool> redHighlights;
std::map<QString, bool> greenHighlights;
std::map<QString, bool> blueHighlights;
signals:
void redChanged();
void greenChanged();
void blueChanged();
private:
};
My understand of Q_PROPERTY is that setting WRITE to setRed, setBlue etc. should mean that when I set hl.red to something, it should call the function I associate with WRITE. However, I have put breakpoints in the code there and that code is never run. When I use console.log to print hl.blue it just prints the string that I tried to pass before. Can anyone clear this up for me? Have I misinterpreted how this works?
EDIT
Here is the code where I associate the HighlightModel with the engine:
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
qDebug() << VERSION_INFO;
FrameViewerWindow engine;
InfoHolder ver;
HighlightModel highlights;
engine.rootContext()->setContextProperty("ver", &ver);
engine.rootContext()->setContextProperty("hl", &highlights);
engine.addImageProvider("images", new ImageLoader(QQuickImageProvider::Image, &highlights));
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
return app.exec();
}