dotNet listview and checkboxes

This is a snippet of code where I want to control the checkboxes by multiple selections in the listview itself and hitting the checkbox (whether it is checked or not) to select / de-select them accordingly, trouble is when I do this it doesn't do them in one but for each item.

Basically, if I shift and select the items and check off the box the value counts down in real-time for the countLabelVal text.

Is there a dotNet way of doing this?

on lv ItemChecked do part of the code below is the trouble maker.

-- This is a snippet of code where I want to control the checkboxes by multiple selections and hitting the checkbox (whether checked or not) to select / de-select them accordingly, trouble is when I do this it doesn't do them in one but for each item. Is there a dotNet way of doing this?

try(destroydialog ::lvRolTest)catch()
rollout lvRolTest "Check Mate.."
(

  local lvSetItemsProp
  local reSizeListView

  label         countLabelPrefix  "How many you say ?" across:3
  label         countLabelVal     ""
  checkButton   ChkLvButton       "Un/check All..."
  dotNetControl lv                "ListView" width:250 height:545 pos:[10,30]

  on lvRolTest open do
  (
    lv.View             = (dotNetClass "View").Details
    lv.FullRowSelect    = true
    lv.GridLines        = true
    lv.MultiSelect      = true
    lv.Checkboxes       = true
    lv.Columns.add      ("Items")

    reSizeListView()

    for x=1 to 100 do
    (
      lv.BeginUpdate()
      local newLvItem = dotNetObject "ListViewItem" ("Item " + x as string)
      newLvItem.checked = true
      lv.EndUpdate()
      lv.items.add newLvItem
      )
    lv.Focus()
    countLabelVal.text = (lv.CheckedItems.count) as string
    )

  on lvRolTest resized val do (
    reSizeListView()
    )

  on ChkLvButton changed state do (
   if state do ChkLvButton.text         = "Check All..."
   lvSetItemsProp rolArg:(#lvRolTest as string) lsArg:(#lv as string) prop:#Checked state:((not state) as string)
   if not state do ChkLvButton.text     = "Uncheck All..."
   countLabelVal.text = (lv.CheckedItems.count) as string
   lv.Focus()
   )

  on lv ItemChecked do
  (
    if lv.CanSelect and lv.CanFocus and lv.Focused then
    (
      lv.BeginUpdate()
      countLabelVal.text = (lv.CheckedItems.count) as string
      lv.EndUpdate()
      )
    )

  fn reSizeListView = (
    lv.width                 = lvRolTest.width-20
    lv.height                = lvRolTest.height-40
    lv.columns.item[0].width = lvRolTest.width-40.5
    )

  fn lvSetItemsProp rolArg:#rolArg lsArg:#lsArg prop:#checked state:#false = (
    execute("for i = 0 to "+rolArg+"."+lsArg+".items.count-1 do "+rolArg+"."+lsArg+".items.item[i]."+prop+"="+state)
    )

  )
createDialog lvRolTest 270 575 style:#(#style_SysMenu, #style_ToolWindow, #style_resizing)

-- lvRolTest.ChkLvButton.state = true