Tk Widgets

This material is best on several sources– Slides by Dr. Ernest J. Friedman-Hill– various Tcl/Tk books

Building User Interfaces With Tk You build interfaces with

– Widget commands buttons, labels, list boxes, text widgets, canvases, etc.

often includes callbacks

– Geometry management widget layout tools

place, pack and grid

– Bindings bind user actions to widgets / objects to invoke commands

– Window Manager commands to control your window

Widgets implemented by Tk

Frame Menubutton CanvasLabel Menu ScrollbarButton Message ScaleCheckbutton Entry ListboxRadiobutton Text Toplevel

Try the Widget Tour on the PCs to get an overviewStart/Tcl/Widget Tour

The Widget Hierarchy

.

.menu.file

.scroll

.menu.help

.menu.listbox

Creating Widgets Each widget has a class: button, listbox, scrollbar, etc.

One class command for each class, used to create instances:button .b -text Quit -command exitscrollbar .x -orient horizontal

class name

window name

configuration options

Configuration Options Defined by class. For buttons:

-activebackground -disabledforeground -justify -underline -activeforeground -font -padx -width -anchor -foreground -pady -wraplength

-background -height -relief-bitmap -highlightbackground -state-borderwidth -highlightcolor -takefocus-command -highlightthickness -text-cursor -image -textvariable

Default provided by class.button .b -text Hello -command exit

button .c -bitmap @$tk_library/demos/images/flagdown.bmp

grid .b .c

Advanced: may be specified in an options database

Widget Commands Tcl command for each widget, named after widget. Used to reconfigure, manipulate widget:

button .b -text "Hello".b configure -text Goodbye

Configurations are readable and modifiable, anytime

–very powerful, as can change anything Widget command is deleted when widget is destroyed.

–destroy .b

Geometry Management Widgets don't control their own

positions and sizes: geometry managers do.

Widgets don't even appear on the screen until managed by a geometry manager.

Geometry manager = algorithm for arranging slave windows relative to a master window.

Constraint-based systemi.e., what to do when widgets / windows change size

GeometryManager

Requested size from slave

Parameters from application designer

Geometry of master

Size and location of slave

Requested size for master

The Placer Simple but not very powerful Each slave placed individually relative to its master. Avoid using it

button .b -text X

place .b -x 0 -y 0

The Grid Lays out objects in virtual grid of rows and columns powerful, but good for most simple placements

entry .e.e insert 0 "Type text here"button .b1 -text "Wow!"button .b2 -text "Ho Hum"grid .e -row 0 -column 0 -columnspan 2 -sticky ewgrid .b1 -row 1 -column 0 grid .b2 -row 1 -column 1

The Grid Another example

label .to_label -text "To:"entry .tolabel .from_label -text "From:"entry .fromtext .t -width 24 -height 10grid .to_label -row 0 -column 0 -sticky egrid .to -row 0 -column 1 -sticky ewgrid .from_label -row 1 -column 0 -sticky egrid .from -row 1 -column 1 -sticky ewgrid .t -row 2 -column 0 -columnspan 2 -sticky nsew

The Packer More powerful than the placer, but more complex Arranges groups of slaves together (packing list). Packs slaves around edges of master's cavity. For each slave, in order:

1. Pick side of cavity.

2. Slice off parcelfor slave.

4. Position slavein parcel.

3. Optionally grow slaveto fill parcel.

The Packer: Choosing Sides

button .ok -text OKbutton .cancel -text Cancelbutton .help -text Help

pack .ok .cancel .help -side left

.cancel configure -text "Cancel Command"

pack .ok .cancel .help -side top

The Packer: Padding

pack .ok .cancel .help -side left \-padx 2m -pady 1m

pack .ok .cancel .help -side left \-ipadx 2m -ipady 1m

pack .ok .cancel .help -side left \-padx 2m -pady 1m -ipadx 2m -ipady 1m

The Packer: Filling

Stretch widgets to fill parcels:

pack .ok .cancel .help -side top

pack .ok .cancel .help -side top -fill x

The Packer: Filling, cont'd

pack .menu -side toppack .scrollbar -side rightpack .listbox

pack .menu -side top -fill xpack .scrollbar -side right -fill ypack .listbox

The Packer: ExpansionIncrease parcel size to absorb extra space in master:

pack .ok .cancel .help -side left

pack .ok .cancel -side leftpack .help -side left \ -expand true -fill x

pack .ok .cancel -side leftpack .help -side left -expand true

The Packer: Expansion, cont'd

pack .ok .cancel .help -side left \ -expand true

pack .ok .cancel .help -side left \ -expand 1 -fill both

Hierarchical PackingUse additional frames to create more complex arrangements:frame .leftpack .left -side left -padx 3m -pady 3mframe .rightpack .right -side right -padx 3m -pady 3m

foreach size {8 10 12 18 24} { radiobutton .pts$size -variable pts \ -value $size -text "$size points"}pack .pts8 .pts10 .pts12 .pts18 .pts24 \ -in .left -side top -anchor w

checkbutton .bold -text Bold \ -variable boldcheckbutton .italic -text Italic \ -variable italiccheckbutton .underline -text Underline \ -variable underlinepack .bold .italic .underline \ -in .right -side top -anchor w

Callbacks How to make widgets work together with application,

other widgets? Tcl scripts. Widget actions are Tcl commands:

button .a.b -command exitexitbutton release

Bindings Associate Tcl scripts with user events:

bind .e <Control-h> {backspace .t}

Window(s) Event Script

Bindings: Specifying Events Specifying events:

<Double-Control-ButtonPress-1>

<3><KeyPress>a

Modifiers Event Type

Button or Keysym

Bindings: Substitutions % substitutions in binding scripts:

– Coordinates from event: %x and %y.– Window: %W.– Character from event: %A.– Many more...

Examples:bind .c <B1-Motion> {move %x %y}bind .t <KeyPress> {insert %A}

Example: Context sensitive help

button .b -text "Hello World" -command exitbutton .c -text "Lazy Boy"label .help pack .b .c .help -side topbind .b <Enter> {.help configure -text "Press to exit"}bind .c <Enter> {.help configure -text "i do nothing"}bind Button <Leave> {.help configure -text ""}

Access To Other Facilities Keyboard focus:

focus .x.y Communication with window manager:

wm title . "Editing main.c"wm geometry . 300x200wm iconify .

Deleting windows:destroy .x

Summary Creating interfaces with Tk is easy:

– Create widgets.– Arrange with geometry managers.– Bind if necessary (rarely need to, except for text and

canvas objects)– window management