qml 自定义滑动条（官方example）

  Rectangle {
      id: frame
      clip: true
      width: 160
      height: 160
      border.color: "black"
      anchors.centerIn: parent

      Text {
          id: content
          text: "ABC"
          font.pixelSize: 169

          MouseArea {
              id: mouseArea
              drag.target: content
              drag.minimumX: frame.width - width
              drag.minimumY: frame.height - height
              drag.maximumX: 0
              drag.maximumY: 0
              anchors.fill: content
          }
      }

      ScrollIndicator {
          id: verticalIndicator
          active: mouseArea.pressed
          orientation: Qt.Vertical
          size: frame.height / content.height
          position: -content.y / content.height
          anchors { top: parent.top; right: parent.right; bottom: parent.bottom }
      }

      ScrollIndicator {
          id: horizontalIndicator
          active: mouseArea.pressed
          orientation: Qt.Horizontal
          size: frame.width / content.width
          position: -content.x / content.width
          anchors { left: parent.left; right: parent.right; bottom: parent.bottom }
      }
  }