import QtQuick 2.3
import QtQuick.Controls 1.4
import QtQuick.Controls.Styles 1.4
import QtQuick.Controls.Private 1.0

Item {
    width: 400
    height: 400
    property bool accelerating : false
    
    Text {
        anchors.centerIn: parent
        text: "Press anywere to accelerate"
    }

    Accelerator {
        id: acc
        anchors.fill: parent
        value: accelerating ? 400 : 0                           // COMMENT OUT THIS 
        Behavior on value {
            NumberAnimation {
                easing.type: Easing.OutCubic
                duration: 3000
            }
        }
    }

    MouseArea {
        anchors.fill: parent
        onPressedChanged: accelerating = pressed                // ...AND COMMENT OUT THIS
        //onPressedChanged: { acc.value = (pressed ? 400 : 0) } // ...AND UNCOMMENT OUT THIS AND IT WORKS
    }
}

import QtQuick 2.3

Rectangle {
    property alias value: range.width
    color: "yellow"
    Text {
        text: 'value: ' + value
    }

    Rectangle {
        id: range
        color: "red"
        width: 0
        height: 5
        anchors.bottom: parent.bottom
    }
}