Como sugerido nesta resposta , prefira o TextField :
O código correspondente:
import QtQuick 2.0
import Ubuntu.Components 0.1
import QtQuick.Controls 1.1
import QtQuick.Controls.Styles 1.1
MainView {
id: main
width: 200
height: 200
TextField {
anchors.centerIn: parent
placeholderText: "0"
text: "0"
horizontalAlignment: TextInput.AlignHCenter
style: TextFieldStyle {
textColor: "black"
background: Rectangle {
radius: 20
color: "#F0EBEB"
implicitWidth: 40
implicitHeight: 24
border.color: "#000000"
border.width: 1
}
}
}
}