QML Screen incorrect properties at application start up

[xanm]

I need correct screen sizes at start but if i do this code:

@import QtQuick 2.0
import QtQuick.Window 2.0

Rectangle {

MouseArea {
    anchors.fill: parent
    onClicked: {
        console.log( Screen.height, Screen.width, Screen.desktopAvailableHeight, Screen.desktopAvailableWidth);
    }
}

Component.onCompleted: {
    console.log( Screen.height, Screen.width, Screen.desktopAvailableHeight, Screen.desktopAvailableWidth);
}

}
@

i have zeros at start
and correct screen sizes at mouse click

@0 0 0 0
1200 1920 1133 1920@

How can tell what is this?
And how i can get correct screen sizes at start of application?

[Eddy]

The answers are in the "QML screen docs":http://qt-project.org/doc/qt-5.0/qtquick/qml-qtquick-window2-screen.html#details