In this code, when I click zoomIn rectangle, the picture does zoom in, but the default scrollbars of ScrollView do not change accordingly. They remain the same. Therefore I cannot scroll the zoomed picture.

http://doc.qt.io/qt-5/qml-qtquick-co...crollview.html

Please point out the fault.

Qt Code: 
  1. Rectangle
  2.     {
  3.          id: zoomIn
  4.          height: 50; width: 50; color: "blue"
  5.          Text { text: qsTr("Zoom In") }
  6.          MouseArea
  7.          {
  8.              anchors.fill: parent
  9.              onClicked:
  10.              {
  11.                  currentPicture.scale += 0.5
  12.              }
  13.          }
  14.     }
  15.  
  16.  
  17.     ScrollView
  18.     {
  19.         id: head
  20.         anchors.top: buttons.bottom
  21.         anchors.topMargin: 30
  22.         height: 300; width: 300
  23.         frameVisible: true
  24.  
  25.         Image
  26.         {
  27.             id: currentPicture
  28.             height: head.height; width: head.width
  29.             source: folderModel1.hh
  30.             z:0
  31.         }
  32.     }
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