You can create checkboxes on tree widgets with the WIDGET_TREE function, using the CHECKBOX keyword. To control the state of the checkboxes, use the CHECKED keyword. The following image shows checked nodes in tree widget nodes. The filled-in squares next to folders indicate a mixed check state, where some child nodes of the folder are checked and some are not.

Checkboxes in a widget tree

Checkbox Example

This example demonstrates a simple tree with checkboxes on some of its nodes. The tree root's event handler adds business logic to set the state of a node's descendants and ancestors. Checking a folder node sets all child nodes to "checked". Unchecking a node changes all ancestors to either "unchecked" or "mixed", depending on the state of other nodes. 

; This routine sets all descendants of a node
; to the given check state.
PRO MY_TREE_UPDATE_DESCENDANTS, node, state
  COMPILE_OPT IDL2
   
  ; Get an array of all child nodes.
  children = WIDGET_INFO( node, /ALL_CHILDREN )
   
  IF ( children[0] EQ 0 ) THEN RETURN
   
  ; Set the check-state of each child and then recursively
  ; update their children
  FOREACH c, children DO BEGIN
    WIDGET_CONTROL, c, SET_TREE_CHECKED = state
    MY_TREE_UPDATE_DESCENDANTS, c, state
  ENDFOREACH
   
END
 
; This routine sets the check state of all tree widget ancestors of a
; node. The main rule is that if all children are checked or
; all are unchecked then the parent gets the check-state of the
; children. If at least one, but not all, children are unchecked
; or mixed then the parent gets the state of mixed.
 
PRO MY_TREE_UPDATE_ANCESTORS, node
  COMPILE_OPT IDL2
   
  ; Get the parent and proceed only if it is a tree widget
  parent = WIDGET_INFO( node, /parent )
   
  IF ( parent NE 0 AND WIDGET_INFO( parent, /type ) EQ 11 ) THEN BEGIN
   
    ; Get statistics on the children:
    ; - number of children that are checked (value of 1)
    ; - number of children that are mixed (value of 2)
    ; - total number of children of any state
    children = WIDGET_INFO( parent, /all_children )
   
    nOnes = TOTAL( WIDGET_INFO( children, /TREE_CHECKED ) eq 1 )
    nTwos = TOTAL( WIDGET_INFO( children, /TREE_CHECKED ) eq 2 )
   
    nChildren = N_ELEMENTS( children )
   
    ; Figure out the state of the parent node
    IF ( nOnes EQ nChildren ) THEN BEGIN
      newState = 1
    ENDIF ELSE IF ( nOnes GE 1 || nTwos GE 1 ) THEN BEGIN
      newState = 2
    ENDIF ELSE BEGIN
      newState = 0
    ENDELSE
   
    ; Apply the new state and recursively repeat on the next ancestor
    WIDGET_CONTROL, parent, SET_TREE_CHECKED = newState
   
    MY_TREE_UPDATE_ANCESTORS, parent
   
  ENDIF
   
END
 
; Create the event handlers
PRO TREE_CHECKBOX_EXAMPLE_EVENT, e
END
PRO HANDLE_TREE_EVENT, e
COMPILE_OPT IDL2
  HELP, e, /STRUCTURE
   
  IF ( e.type EQ 2 ) THEN BEGIN
   
     MY_TREE_UPDATE_DESCENDANTS, e.id, e.state
     MY_TREE_UPDATE_ANCESTORS, e.id
   
  ENDIF
   
END
 
; This is the widget creation routine
PRO TREE_CHECKBOX_EXAMPLE
  COMPILE_OPT IDL2
   
  ; Create a top level base
  topLevelBase = WIDGET_BASE( $
     XOFFSET = 200, YOFFSET = 100 )
   
  ; Create the tree
  root = WIDGET_TREE( topLevelBase, $
     event_pro = 'HANDLE_TREE_EVENT' )
   
  ; Create the first folder without a checkbox
  f1 = WIDGET_TREE( ROOT, /FOLDER, /EXPANDED, VALUE = 'Folder 1' )
   
  ; Create the nodes with checkboxes.
  ; Check some of the boxes (CHECKED = 1)
  n11 = WIDGET_TREE( f1, VALUE = 'Node 11', /CHECKBOX, CHECKED = 0 )
  n12 = WIDGET_TREE( f1, VALUE = 'Node 12', /CHECKBOX, CHECKED = 1 )
  n13 = WIDGET_TREE( f1, VALUE = 'Node 13', /CHECKBOX, CHECKED = 0 )
  n14 = WIDGET_TREE( f1, VALUE = 'Node 14', /CHECKBOX, CHECKED = 1 )
   
  ; Create the second folder and child nodes with checkboxes.
  ; Checkboxes are not checked on creation.
  f2 = WIDGET_TREE( ROOT, /FOLDER, /EXPANDED, /CHECKBOX, VALUE = 'Folder 2' )
  n21 = WIDGET_TREE( f2, VALUE = 'Node 21' )
  f22 = WIDGET_TREE( f2, /FOLDER, VALUE = 'Folder 22' )
  n221 = WIDGET_TREE( f22, VALUE = 'Node 221' )
  n222 = WIDGET_TREE( f22, VALUE = 'Node 222' )
  n23 = WIDGET_TREE( f2, VALUE = 'Node 23' )
   
  ; Realize the widgets
  WIDGET_CONTROL, topLevelBase, /REALIZE
   
  XMANAGER, 'TREE_CHECKBOX_EXAMPLE', topLevelBase, /NO_BLOCK
   
END