import QtQuick 2.15
import QtQuick.Window 2.15
import QtQuick.Controls 2.15

Window {
    id: window
    width: 640
    height: 480
    visible: true

    Dialog{
        id: dialog
        width: 400; height: 400
        Rectangle{
            anchors.fill: parent
            Rectangle{
                id: rect
                color: "red"
                width: 20;
                height: 20;
            }
            DragHandler{
                target: rect
            }
        }
    }
    Component.onCompleted: dialog.open()
}