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[Tim Peeters <1494387@xxxxxxxxxxxxxxxxxx>]

More people run into problems here: http://pastebin.ubuntu.com/12417204/

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https://bugs.launchpad.net/bugs/1494387

Title:
  CheckBox needs to track external properties

Status in ubuntu-ui-toolkit package in Ubuntu:
  Confirmed

Bug description:
  Often a CheckBox/Switch is used to show the value of a property
  outside of the CheckBox. For example:

  Switch {
      id: hiddenSwitch
      checked: !header.exposed
      onClicked: header.exposed = !header.exposed
  }

  At first look, this code may seem fine, but clicking the switch will
  trigger checked = !checked, which breaks the binding, so if
  header.exposed updates because of events happening outside of the
  switch, the switch will be out-of-sync.

  Perhaps we need to add some properties to the CheckBox:

  CheckBox {
    property Object bindTarget
    property string bindProperty
  }

  and then the behavior of this:
  Switch {
      id: exposedSwitch
      bindTarget: header
      bindProperty: "exposed"
  }

  can do what we want: the switch shows the value of "exposed", and
  clicking the switch should update the "exposed" value (which in turn
  will update the state of the switch).

  Note that in this case we could not track "!exposed", so if we need
  that, some more complicated solution is needed.

  --- update 2015-09-11 (thanks Christian) ---
  It appears to work like this:
  Switch {
      id: hiddenSwitch
      checked: header.exposed
      function trigger() { header.exposed = !header.exposed; }
  }

  so DON'T use the onClicked or onTriggered signal as you would expect,
  but override the trigger() function. We need to document this.

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