Geometry Managers

A geometry manager manages the placement and layout of the elements of a GUI.

Reading edit

Windownamager geometry problem , comp.lang.tcl ,2002-06-04: KBK gives a good description of the requested versus the actual geometry of a widget

Tk geometry managers edit

place: precise placement of a widget in absolute coordinates, for when you want to roll your own geometry manager
pack: widgets flow around each other in the available space
grid: available space is devided into numbers sectors to which widgets are either manually or automatically assigned. Somewhat more direct and intuitive than pack.

The text and canvas widgets also have a limited capability to manage the geometry of child widgets (without using place, pack or grid). For example, BWidget constructs a scrollable frame megawidget by creating a frame as an embedded window of a canvas.

Other Geometry Managers edit

BLT's table geometry manager
layout: a Tk front-end that calls the standard geometry managers with a different interface
Tix's form geometry manager
TkVSform: does geometry management (along with other things) for its forms
GRIDPLUS2: is a screen layout package built on the Tk grid manager
making your own geometry manager

Description edit

Choose grid for tabular layouts, and when there's no good reason to choose something else. Choose pack if you're used to the web browser box model, and the flow makes sense to you. Choose place when you want as little help as possible managing the layout.

Introspection edit

Introspection on geometry managers is possible:

winfo manager $widget

Notice that

winfo manager $toplevel

returns the special value, wm.

Horizontal Stretch of One Widget, But No Vertical Stretch of Either Widget edit

Harald Kirsch: Is it possible with place to position a widget .f.bot just below another widget .f.top such that the following holds:

If the container .f is resized vertically, both widgets keep their natural height and keep sticked to the top of .f
If .f is resized horizontally, .f.top keeps it natural width and stays sticked to the left border of .f while .f.bot resizes itself to stretch over the whole width of .f.

Please note that 2 seems to make it impossible to use the sibling-trick mentioned in the place-manual.

I would probably get the above done with place, if I knew a way of extracting the natural width and height of widgets which are [place]d. Neither [... cget -width] nor [winfo width ...] deliver anything useful - except if I call update before calling winfo.

ANSWER - DKF

You need to use [winfo reqwidth]. Code that satisfies your request follows:

# Basic Setup
frame .f -bg red
label .f.top -text "I'm top" -bg yellow
label .f.bot -text "I'm bot" -bg white
pack .f -fill both -expand 1
# Geometry Manager Magic
set w1 [winfo reqwidth .f.top]
set w2 [winfo reqwidth .f.bot]
if {$w1<$w2} {set w1 $w2}
set h [expr {[winfo reqheight .f.top]+[winfo reqheight .f.bot]}]
.f configure -width $w1 -height $h
place .f.top -x 0 -y 0
place .f.bot -x 0 -y [winfo reqheight .f.top] -relwidth 1

Did you know that you can also achieve the same effect using grid?

# Basic Setup
frame .f -bg red
label .f.top -text "I'm top" -bg yellow
label .f.bot -text "I'm bot" -bg white
pack .f -fill both -expand 1
# Geometry Manager Magic
grid .f.top -sticky w
grid .f.bot -sticky ew
grid columnconfigure .f 0 -weight 1
grid rowconfigure .f 2 -weight 1 -minsize 0

And also pack?

# Basic Setup
frame .f -bg red
label .f.top -text "I'm top" -bg yellow
label .f.bot -text "I'm bot" -bg white
pack .f -fill both -expand 1
# Geometry Manager Magic
pack .f.top -side top -anchor w
pack .f.bot -side top -anchor nw -fill x -expand 1

DKF:

Many widgets have -width and -height options, but those do not usually give useful results when read (for the purposes of geometry management.) winfo width and winfo height would be more useful you'd think, but in fact they only ever report the current size of a widget, which is initially zero as there hasn't been time to work it out yet (since interaction with geometry managers is performed on idle updates.) To get the info you need for GM, you need winfo reqheight and winfo reqwidth commands, which report what size widgets would prefer to be.

The other thing you need to watch out for if you are doing any fancy geometry mangling (unlike the simple example above) is the <Configure> event. This lets you find out when the enclosing widget changes in size due to whatever GM is managing it. A sophisticated example that uses the configure events is available at [1].

KBK: You also need to include update idletasks in the case where another geometry manager is managing the winfo reqwidth or winfo reqheight of the widget. It is possible that the requested size is zero because a subordinate geometry manager hasn't had the chance to work out the size.

Using Text Widget As a Flowing Geometry Manager edit

[Michail Richardson]: Is it possible with pack to position a series of widgets in a frame such that if they all fit in the horizontal space, then they are arranged that way. Otherwise, they are folded like text. A sort of message window for frames. This is so that a series of radiobuttons that exceeds the width of the user's screen can properly be displayed, in, e.g. tkGnats. (The list of buttons is determined at run-time)

KBK: Sure. Window them in a text widget. There's an example in the "Widget Tour" that comes with Tk that does just what you're asking.

escargo: This sounds like the Java flow layout.

Using pack and grid Together edit

Lars H: In the following example, the main structure uses grid, but the "toolbar" frame on the top uses pack internally. Widgets named something ending in _c are canvases, ending in _h horizontal scrollbars, and those ending in _v are vertical scrollbars.

set t [toplevel .rulebrowser]
wm title $t "Rule browser"

# First create some things to manage
foreach c_ [list $t.left_ $t.right_] {
   scrollbar ${c_}h -orient horiz -command [list ${c_}c xview]
   scrollbar ${c_}v -command [list ${c_}c yview]
   canvas ${c_}c -width 200 -height 400 -relief solid -borderwidth 1\
     -xscrollcommand [list ${c_}h set] -yscrollcommand [list ${c_}v set]\
     -scrollregion {0 0 300 500}
}

# Then start managing
grid $t.left_c  -row 2 -column 0 -sticky nsew
grid $t.right_c -row 2 -column 3 -sticky nsew
grid $t.left_v  -row 2 -column 1 -sticky ns
grid $t.right_v -row 2 -column 4 -sticky ns
grid $t.left_h  -row 3 -column 0 -sticky ew
grid $t.right_h -row 3 -column 3 -sticky ew
grid rowconfigure $t 2 -weight 1
grid columnconfigure $t 0 -weight 1
grid columnconfigure $t 3 -weight 1

canvas $t.arrow_c -width 20 -height 20
$t.arrow_c create line {0 10 20 10} -arrow last -width 2
grid $t.arrow_c -row 2 -column 2

scrollbar $t.text_v -command [list $t.text_t yview]
text $t.text_t -height 5 -yscrollcommand [list $t.text_v set]
grid $t.text_t - - - -row 1 -column 0 -sticky nsew
grid $t.text_v -row 1 -column 4 -sticky ns

set bg grey90
frame $t.f -background $bg
grid $t.f - - - - -row 0 -column 0 -sticky ew
pack [button $t.f.prev -text "Prev" -highlightbackground $bg] -side left
pack [button $t.f.next -text "Next" -highlightbackground $bg] -side left
pack [button $t.f.go -text "Go" -highlightbackground $bg] -side right
pack [entry $t.f.go_e -width 4] -side right
pack [label $t.f.go_l -text "Rule" -background $bg] -side right

Misc edit

escargo: Is there any way to tell which of the commands (or potentially procedures) act as geometry managers? (This is in some respects an Introspection question as well.)

escargo 2003-07-01: Apparently not. Darn.

Category GUI

See Also edit