how to change the dayDelegate for changing the image visible state?

[nicker player]

 style: CalendarStyle {

                dayDelegate: Item {
                    id: calendarItem
                    readonly property color sameMonthDateTextColor: "#444"
                    readonly property color selectedDateColor: Qt.platform.os
                                                               === "osx" ? "#3778d0" : "#d7d9dB"
                    readonly property color selectedDateTextColor: "white"
                    readonly property color differentMonthDateTextColor: "#bbb"
                    readonly property color invalidDatecolor: "#dddddd"

                    Rectangle {
                        anchors.fill: parent
                        border.color: "transparent"
                        color: styleData.date !== undefined
                               && styleData.selected ? selectedDateColor : "transparent"
                        anchors.margins: styleData.selected ? -1 : 0
                    }

                    Image {
                        id: markedImage
                        visible: eventModel.eventsForDate(
                                     styleData.date).length > 0
                        anchors.top: parent.top
                        anchors.left: parent.left
                        anchors.margins: -1
                        width: 12
                        height: width
                        source: "qrc:/qss/res/img/ui/eventindicator.png"
                    }

                    Label {
                        id: dayDelegateText
                        text: styleData.date.getDate()
                        anchors.centerIn: parent
                        color: {
                            var color = invalidDatecolor
                            if (styleData.valid) {
                                // Date is within the valid range.
                                color = styleData.visibleMonth ? sameMonthDateTextColor : differentMonthDateTextColor
                                if (styleData.selected) {
                                    color = selectedDateTextColor
                                }
                            }
                            color
                        }
                    }
                }

the example what the qt offered that named the calendar of the qml.
i just want to refresh the state of the calendar for some days state.the dayDelegate called the

eventModel.eventsForDate(styleData.date).length > 0

how to change the visible state ?the method upstairs