What's wrong with the tree widgets?

dzach: Or, more accurately, what's wrong with tree widgets representing file structures and the alike?

  • Natural trees have roots, branches, leaves and fruits.
  • Roots grow branches.
  • Branches grow branches, leaves and fruits.
  • Branches are paths for juices to reach the leaves and fruits.
  • Leaves are an end to themselves. They grow chlorophyll.
  • Fruits are the hope for future generations. That's why they are initially beautiful flowers; they are the center of a lot of activity and go through a lot of changes.
  • Fruits finally grow seeds.
  • Seeds will some day grow trees of their own.

But is this how a tree widget looks and behaves? Usually not.

A common tree widget can have a root, and branches. Branches can grow, with the press of little '+'s or shrink when you press little '-'s, if there is something more that they hold. But then, suddently, while trying to expand a branch, we get a fruit pop open. This is totally strange.

Expanding a branch to reveal seeds breaks the tree metaphor. Branches, usually, don't grow to become seeds; one needs to open the fruit to find seeds. The little '+'s and '-'s have to operate on fruits (folders) not on branches, when seeds are expected. Expanding a branch and expanding a folder are different functions.

To make all these more obvious, a hack of tktree is used to implement different appearances. That's right. Only appearances. It shifts the '+' or '-' graphic to the right of the folder icon by introducing a -displace option. The result may be convincing; after all, there are many implementations around, of trees done the 'right' way. But if at the end all these have not convinced you, hey, no problem! this is a nice, colorful Darwinian world, full of evolutionary surprises! Branches that grow to seeds is only one of many possibilities :-)

http://users.hol.gr/~dzach/deepconsole/tree.png http://users.hol.gr/~dzach/deepconsole/tree0.png

Hacked tktree code:

     package require Tk
      namespace eval ::tktree {

        # Images used for open and close state of subgroups
        set ::tktree::imgcollapse [image create photo .tktreeopenbm -data {
        set ::tktree::imgexpand [image create photo .tktreeclosebm -data {
        ###Default images for groups and children
        set ::tktree::imgsubgroups [image create photo .tktreeimgfolder -data {
        set ::tktree::imgchildren [image create photo .tktreeimgfile -data {

        #### Swtich all subgroups of a layer to open or close
        proc ::tktree::switchlayer {win opn {layer /}} {
          variable cfg
          foreach child $cfg($win,$layer:subgroups) {
            set cfg($win,$child:open) $opn
            switchlayer $win $opn $child
          buildwhenidle $win

        ####  will open or close the item given
        proc ::tktree::switchstate {win item} {
          set ::tktree::cfg($win,$item:open) [expr ! $::tktree::cfg($win,$item:open)]
          buildwhenidle $win

        #### Select the next item up or down
        proc ::tktree::updown {win down} {
          variable cfg
          set index [lsearch -exact $cfg($win,sortlist) $cfg($win,selection)]
          if {$down} {incr index} {incr index -1}
          if {$index < 0} {set index end} elseif {$index >= [llength $cfg($win,sortlist)]} {set index 0}
          setselection $win [lindex $cfg($win,sortlist) $index]

        #### left-right button binding commands
        proc ::tktree::leftright {win right} {
          variable cfg
          set item $cfg($win,selection)
          set index [lsearch -exact $cfg($win,sortlist) $item]
          set parentindex [lsearch -exact $cfg($win,sortlist) [file dirname $item]]
          if {$parentindex == -1} {set parentindex [expr $index - 1]}
          if {$cfg($win,$item:group)} {
            if {$right} {
              if {$cfg($win,$item:open)} {incr index} {set cfg($win,$item:open) 1}
            } else {
              if {$cfg($win,$item:open)} {set cfg($win,$item:open) 0} {set index $parentindex}
          } else {
            if {$right} {incr index} {set index $parentindex}
          if {$index < 0} {set index end} elseif {$index >= [llength $cfg($win,sortlist)]} {set index 0}
          setselection $win [lindex $cfg($win,sortlist) $index]
          buildwhenidle $win

        #### will return the pathname of the item at x and y cooridinates
        proc ::tktree::labelat {win x y} {
          set x [$win canvasx $x]; set y [$win canvasy $y]
          foreach m [$win find overlapping $x $y $x $y] {
            if {[info exists ::tktree::cfg($win,tag:$m)]} {return $::tktree::cfg($win,tag:$m)}
          return ""

        #### will return the path of the current selection in the given tree widget
        proc ::tktree::getselection {win} {
          return $::tktree::cfg($win,selection)

        #### adjust the scrollview to show the selected item as needed
        proc ::tktree::scrolladjust {win tag} {
          set item [$win bbox $tag]
          set region [$win cget -scrollregion]
          foreach {axis idx1 idx2} {yview 1 3 xview 0 2} {
            set range [expr abs([lindex $region $idx2]) - abs([lindex $region $idx1])]
            set itemtop [lindex $item $idx1];  set itembot [lindex $item $idx2]
            set viewtop [expr $range * [lindex [$win $axis] 0]]
            set viewbot [expr $range * [lindex [$win $axis] 1]]
            if {$itembot > $viewbot} {$win $axis moveto [expr ($itembot. - $viewbot + $viewtop) / $range]}
            if {$itemtop < $viewtop} {$win $axis moveto [expr $itemtop. / $range]}

        #### will set the current selection to the given item on the given tree
        proc ::tktree::setselection {win item} {
          variable cfg
          if {![llength $cfg($win,sortlist)]} {return}
          if {$item eq ""} {set item [lindex $cfg($win,sortlist) 0]}
          if {![info exists cfg($win,$item:tag)]} {set item [lindex $cfg($win,sortlist) 0]}
          if {[$win gettags $cfg($win,$item:tag)] ne ""} {
            $win select from $cfg($win,$item:tag) 0
            $win select to $cfg($win,$item:tag) end
            set cfg($win,selection) $item
            scrolladjust $win $cfg($win,$item:tag)
          } {
            setselection $win "/[lindex $cfg($win,/:sortlist) 0]"

        #### will delete the item given from the tree given
        proc ::tktree::delitem {win item} {
          variable cfg
          if {$item eq "/"} {
            array unset cfg $win,* ; catch {destroy $win}
          } {
            set group [file dirname $item]
            if {$cfg($win,$item:group)} {set type subgroups} {set type children}
            set index [lsearch -exact $cfg($win,$group:$type) $item]
            set cfg($win,$group:$type) [lreplace $cfg($win,$group:$type) $index $index]
            array unset cfg $win,$item*
            buildwhenidle $win

        #### create a new item in the tree and rebuild the widget
        proc ::tktree::newitem {win item args} {
          variable cfg
          if {[string index $item 0] ne "/"} {set item /$item}
          if {[string index $item end] eq "/"} {
            set subgroup 1
            set type subgroups
            set item [string range $item 0 end-1]
            set cfg($win,$item:command) [list ::tktree::switchstate $win $item]
          } {
            set subgroup 0
            set type children
            set cfg($win,$item:command) {}
          #Build parent group if needed
          set group [file dirname $item]
          if {![info exists cfg($win,$group:open)]} {newitem $win "$group\/"}
          lappend cfg($win,$group:$type) $item
          #Configure the new item
          set cfg($win,$item:group) $subgroup
          set cfg($win,$item:subgroups) {}
          set cfg($win,$item:children) {}
          set cfg($win,$item:sortlist) {}
          set cfg($win,$item:tags) {}
          set cfg($win,$item:open) 0
          set cfg($win,$item:image) {}
          set cfg($win,$item:textcolor) $cfg($win,textcolor)
          set cfg($win,$item:font) $cfg($win,font)
          set cfg($win,$item:offset) 0
          if {$cfg($win,images)} {set cfg($win,$item:image) [eval list \$::tktree::img$type]}
          foreach {confitem confval} $args {
            switch -exact -- $confitem {
              -textcolor  {set cfg($win,$item:textcolor) $confval}
              -command    {set cfg($win,$item:command)   $confval}
              -image      {set cfg($win,$item:image)     $confval}
              -font       {set cfg($win,$item:font)      $confval}
              -displace   {set cfg($win,$item:displace)  $confval}
          buildwhenidle $win

        #### Draw the given layer of the tree on the canvas starting at xposition
        proc ::tktree::buildlayer {win layer xpos} {
          variable cfg
          set displace $cfg($win,displace)
          #Record y positions for vertical line later on
          set ystart $cfg($win,y); set yend $cfg($win,y)
          if {$layer eq "/"} {set cfg($win,sortlist) ""}
          foreach child $cfg($win,$layer:sortlist) {
            lappend cfg($win,sortlist) $child
            #Check spacing required for images
            set imgwidth 0; set imgheight 0
            if {[string length $cfg($win,$child:image)]} {
              set imgwidth [expr  ([image width $cfg($win,$child:image)] + 2) / 2]
              set imgheight [expr ([image height $cfg($win,$child:image)] + 2) / 2]
            #find X-axis points for image, horiz line, and text
            if {$imgwidth} {
              set centerX [expr $imgwidth + $xpos + 7]
              set rightX  [expr $xpos + 7]
              set textX   [expr {($imgwidth * 2) + $xpos + 10 + $cfg($win,displace)/3}]
            } {
              set centerX [expr $xpos + 10]
              set rightX  [expr $centerX + 4]
              set textX   [expr $rightX + 1]
            #Find the proper amount to increment the y axis
            set fontheight [lindex [font metrics $cfg($win,$child:font)] 5]
            set yincr [expr ($fontheight + 1) / 2]
            if {$imgheight > $yincr} {set yincr $imgheight}
            incr cfg($win,y) $yincr
            #Draw the horizonal line
            $win create line $xpos $cfg($win,y) $rightX $cfg($win,y) -fill $cfg($win,linecolor)
            set yend $cfg($win,y)
            #Draw the image, if it exists
            if {$imgwidth} {
              set it [$win create image $centerX $cfg($win,y) -image $cfg($win,$child:image)]
              $win bind $it <1> [list ::tktree::setselection $win $child]
            #Draw text and store tags for reference
            set cfg($win,$child:tag) [$win create text $textX $cfg($win,y) \
                -text [file tail $child] -font $cfg($win,$child:font) -anchor w -tags x -fill $cfg($win,$child:textcolor)]
            set cfg($win,tag:$cfg($win,$child:tag)) $child
            #Command binding
            $win bind $cfg($win,$child:tag) <1> [list ::tktree::setselection $win $child]
            $win bind $cfg($win,$child:tag) <Double-1> $cfg($win,$child:command)
            #next step up on the y axis
            incr cfg($win,y) $yincr
            #If its a group, add open-close functionality
            if {$cfg($win,$child:group)} {
              if {$cfg($win,$child:open)} {set img collapse} {set img expand}
              set ocimg [$win create image [expr {$xpos+$cfg($win,displace)}] [expr $cfg($win,y) - $yincr] -image [eval list \$::tktree::img$img]]
              $win bind $ocimg <1> [list ::tktree::switchstate $win $child]
              if {$cfg($win,$child:open)} {buildlayer $win $child $centerX}
          #Vertical line
          $win lower [$win create line $xpos [expr $ystart - 7] $xpos $yend -fill $cfg($win,linecolor)]

        #### sort the layer by subgroups then children
        proc ::tktree::sortlayer {win {layer /}} {
          variable cfg
          set cfg($win,$layer:subgroups) [lsort -dictionary $cfg($win,$layer:subgroups)]
          set cfg($win,$layer:children) [lsort -dictionary $cfg($win,$layer:children)]
          set cfg($win,$layer:sortlist) [join [list $cfg($win,$layer:subgroups) $cfg($win,$layer:children)]]
          foreach group $cfg($win,$layer:subgroups) {sortlayer $win $group}

        #### build the tree at the given path
        proc ::tktree::buildtree {win} {
          variable cfg
          $win delete all
          sortlayer $win
          set xpos 5
          set cfg($win,y) 5
          #Draw global expand/contract button, if needed
          if {[string length $cfg($win,/:subgroups)] && $cfg($win,expandall)} {
            set exp 0
            foreach subgroup $cfg($win,/:subgroups) {incr exp $cfg($win,$subgroup:open)}
            if {$exp} {set type collapse} {set type expand}
            set ocimg [$win create image 1 1 -image [eval list \$::tktree::img$type] -anchor w]
            $win bind $ocimg <1> [list ::tktree::switchlayer $win [expr ! $exp]]
          #Build the layers and set initial selection
          buildlayer $win / $xpos
          $win config -scrollregion [$win bbox all]
          setselection $win $cfg($win,selection)

        #### internal use - set up a handle to build the tree when everything is idle
        proc ::tktree::buildwhenidle {win} {
          catch {after cancel $::tktree::cfg($win,buildHandle)}
          set ::tktree::cfg($win,buildHandle) [after idle [list ::tktree::buildtree $win]]

        #### will create a new tree widget at the given path
        proc ::tktree::treecreate {win args} {
          variable cfg
          #Default configuration for new tree
          set cfg($win,selection) {}
          set cfg($win,selidx)    {}
          set cfg($win,/:subgroups) {}
          set cfg($win,/:children) {}
          set cfg($win,/:open)     1
          set cfg($win,images)     1
          set cfg($win,expandall)  1
          set cfg($win,linecolor)  black
          set cfg($win,textcolor)  black
          set cfg($win,displace)   0
          set cfg($win,font) {-family Helvetica -size 10}
          #Parse and setup custom configuration options
          set canvascfg ""
          foreach {item val} $args {
            switch -- $item {
              -linecolor            {set cfg($win,linecolor) $val}
              -textcolor            {set cfg($win,textcolor) $val}
              -font                 {set cfg($win,font)      $val}
              -images               {set cfg($win,images)    $val}
              -expandall            {set cfg($win,expandall) $val}
              -displace             {set cfg($win,displace)  $val}
              default               {lappend canvascfg $item $val}
          #Build the canvas
          eval {canvas $win -takefocus 1 -highlightthickness 0 -highlightcolor #008080} $canvascfg
          bind $win <Destroy> [list ::tktree::delitem $win /]
          bind $win <1>  [list focus $win]
          bind $win <Return> {eval $::tktree::cfg(%W,[::tktree::getselection %W]:command)}
          bind $win <space> {eval $::tktree::cfg(%W,[::tktree::getselection %W]:command)}
          bind $win <Up>    [list ::tktree::updown $win 0]
          bind $win <Down>    [list ::tktree::updown $win 1]
          bind $win <Left>    [list ::tktree::leftright $win 0]
          bind $win <Right>    [list ::tktree::leftright $win 1]

          #Build the tree when idle
          buildwhenidle $win

     ## COMMANDS:
     ##    a quick note about arguements:
     ##     pathname = the qualified tk window pathname for the canvas widget
     ##     itempath = the full path for a tree item
     ##        the tree separtes groupings with a "/" therefore pathnames are as follows
     ##        /item1 is a child on the root of the tree
     ##        /goup1/ is a subgroup on the root level of the tree
     ##        /group1/group2/item1  is a child in the subgroup group2 of the subgroup group1
     ##  ::tktree::treecreate pathname [options]
     ##    will create a new tree widget with the given window pathname
     ##      optional arguments:
     ##        -linecolor            = The color of the branching lines (black)
     ##        -textcolor            = text color (black)
     ##        -font                 = the font for the text (Helvetica size 10)
     ##        -images               = set to 0 to disable images, defaults to 1
     ##        -expandall            = set to 0 to turn off the expand/collapse all button at the top
     ##    **All other arguements are passed to the canvas
     ##  ::tktree::newitem pathname itempath [options]
     ##    will create the new item given by itempath, and rebuild the widget
     ##        if an itempath is given with a group that does not exist, the group will be created
     ##      optional arguments:
     ##        -textcolor = the color for the text (defaults to the default tree color, see treecreate)
     ##        -command   = the command to be executed on a double-1 for the item
     ##                     if it is a group, the default command will open/close the group
     ##        -image     = the path of an image to be drawn as an icon for the item
     ##                        by default an image is drawn (folder or file)
     ##                        set the option to null for no image
     ##        -font      = font for the particular item (defaults to the default tree font, see treecreate)
     ##  ::tktree::delitem pathname itempath
     ##    will delete the item given and rebuild the widget
     ##    if the item is a group, all subgroups and children will also be deleted
     ##    if the item is root (/), then all elements of the tree will be deleted
     ##  ::tktree::labelat pathname xpos ypos
     ##    returns the name of the item at xpos and ypos coordinates
     ##  ::tktree::getselection pathname
     ##    returns the current sselection
     ##  ::tktree::setselection pathname itempath
     ##    set the current selection to the item given
     ## BINDINGS:
     ##  canvas <destroy>            delitem will be called for the root path
     ##  item <button-1>             will change the selection to the item under the cursor
     ##  plus/minus box <button-1>   on a group will change the state of that group (opened or closed)
     ##                              the plus/minus at the top of the widget will expand/collapse recursively
     ##  <double-1><Return><space>   all will launch the command specified for that item (groups switchstate by default)
     ##  <Up><Down><Left><Right>     navigation of the tree widget

    ::tktree::treecreate .tree -height 150 -width 120
    pack .tree -expand 1 -fill both -padx 5 -pady 5 -side left
    focus .tree
    foreach item {/group1/item1 /group1/item2 /group1/subgroup/item1 /group2/item1 /item1} {
        ::tktree::newitem .tree $item -command [list tk_messageBox -message "$item executed"]

    ::tktree::treecreate .tree1 -displace 30 -height 150 -width 120
    pack .tree1 -expand 1 -fill both -padx 5 -pady 5 -side left
    focus .tree1
    foreach item {/group1/item1 /group1/item2 /group1/subgroup/item1 /group2/item1 /item1} {
        ::tktree::newitem .tree1 $item -command [list tk_messageBox -message "$item executed"]
    ::tktree::treecreate .tree2 -displace 20 -height 150 -width 120
    pack .tree2 -expand 1 -fill both -padx 5 -pady 5 -side left
    focus .tree2
    foreach item {/group1/item1 /group1/item2 /group1/subgroup/item1 /group2/item1 /item1} {
        ::tktree::newitem .tree2 $item -command [list tk_messageBox -message "$item executed"]

What´s wrongest with most trees (e.g. Bwidget) is that you can´t have bigger items (e.g. images, menus, multi-lined labels) as nodes. Also, it would be helpful to customize the lines depending on node.

NB: Not every tree is a directory/file tree.

dzach: Sure it's not. What is interesting is the notion that a branch grows to branches while a fruit grows to fruits (folders) or seeds (files), which is content. I would expect branches, i.e. lines in the tree widget, to represent connectivity, not content. A network could be ideally represented in a tree widget where branches expand to more branches, at network nodes (the '+' and '-' expansion/collapse icons). But to have branches expand to content, is rather odd.

escargo 20 Sep 2005 - Somebody hacked out the more recent content of this page. It's not clear if this was intentional or appropriate. Perhaps it should be restored.

Restored page.

Schnexel: That was mestupid. Sorry. I confused the textarea with a forum quote feature.

Hm, sorry -- after 2nd thought I´m not really sorry for crossing out dzach´s little homework. That accident was right to my point: I´m fed up with all those halfdemented IT gadgets. Somehow all you programmer guys seem to be content with those late 20th century primitive tree thingies you learnt from Windoze Explorer.

I have a prototype of a multicolored tree with menus popping up inside the tree and leaves having properties. (The tree was for some database experiment, leaves being db records.) Herewith I promise to polish it and publish some day.

Up to that glorious day I will have to work with BWidget tree, in order to not waste the project´s other developers´ time. My leaves (or dzach´s seeds) are elements of a graphic. It would be unimaginable IT luxury to have the properties of those elements (e.g. visibility, color, labels) editable inside the tree.

dzach: I'm sure we are getting there, any day now. Eager to see your chlorophyll :-) Schnexel: Will take some months of osmosis and sorting (no much daytime for that) -- so don´t hold your breath. Will be ca. 2000 lines. Perhaps I post portions (basic data structuring) early.

dzach 25-9-2005: Continuing on the idea of changing the tree widget's appearance and behaviour, we can try it on different concepts like, for instance, program structure and flow. Here is an interesting result:


An application based on this idea appears in a Deep Console.

dzach: Here is another proof of concept demo on the Deep Console idea, this time including the global namespace (with variables and procs) and the tk extension space (including windows and binds). The third toolbar icon is "after"s, but it doesn't work at this moment. The demo displays its own structure and is editable.

http://users.hol.gr/~dzach/deepconsole/ns.png http://users.hol.gr/~dzach/deepconsole/win.png

The "in-place" editing has been replaced with "hyper-editing": <Double-Button-1> or <Alt-Key-Right> on a highlighted word takes you to that proc. <Button-3> or <Alt-Key-Left> get's you back where you were before. <Alt-Key-Down> opens a textbox for notes, and <Alt-Key-Up> closes it. <Control-w> saves the notes to disk. <Control-s> saves the editbox contents and applies them to the demo (try the widget configurations). This is a suggestion on how a "modern" GUI for tkinspect could look.

Unfortunately, hacking an existing widget which was written for a simpler job, does present limitations on how far one can go. Dealing with the connectors is one, which prevents them from easily becoming "active" and containing data (e.g. weight, filters etc).

The code for the demo is here [L1 ]