Chapter 33. A Perl/Tk Roadmap
While editing TPJ, I often had trouble finding authors to write good beginner articles. I knew plenty of experts, but they usually preferred articles that displayed their expertise. Paradoxically, good articles on simple topics can be hard for experts to write, because it’s been a long time since they were beginners and they may not remember all of the pitfalls they encountered when they started out.
Steve Lidie, the author of most of the articles in this section, doesn’t have that problem: he’s written for both beginners and experts. As I write this, he just finished Mastering Perl/Tk for O’Reilly (co-authored with Nancy Walsh), which adapted five of his ten TPJ articles that were originally planned for this section. We didn’t feel right having similar Perl/Tk material appear in two of our books, so now you’ll have to settle for me.
I’m an intermediate Perl/Tk programmer. Every so often I need to create an interactive graphical application, which I always find I can slap together quickly with Perl/Tk. But I do it infrequently enough that I forget the names of all the widgets and functions, and the order of their parameters. This makes me an unimpressive Perl/Tk programmer, but it has a hidden silver lining—the lack of familiarity with the material allows me to help novices learning Perl/Tk for the first time.
The goal of this article is modest: I’m going to give a nearly code-free roadmap to the Perl/Tk universe, explain what I think is important and what isn’t, and then step out of the way so that Steve, the expert, can show you how it’s done in subsequent articles.
Understand the Basics
Perl/Tk applications are Perl programs that use the
Tk module. There are three basic concepts in
Perl/Tk programming that distinguish it from regular Perl
programming.
Perl/Tk is all about widgets. (“Widget” is a name used for something when you can’t think of anything else to call it.) In Perl/Tk, widgets are graphical elements like buttons, scrollbars, and menus.
Perl/Tk is event-driven. Most of your programs will have a
MainLoopstatement in them; when Perl executes it, your application will go into stasis, taking action only in response to user-created events such as mouse clicks or key presses.Perl/Tk makes extensive use of callbacks. For instance, when you create a button, you have to tell Perl/Tk what Perl code to execute when the user presses that button. The following expression creates a callback that prints
You pressed a button.$mw->Button( -text => "Press me!", -command => sub { print "You pressed a button." } );
Ignore What You Don’t Need
Perl/Tk is huge, and you shouldn’t care. Chances are you only need a tiny subset to create your application. By my count, there are 39 basic widgets, and I almost always get by with just nine (Button, Canvas, Dialog, Frame, Label, MainWindow, Menu, Text, and TopLevel).
Some other Perl/Tk features I’ve never needed:
The ability to create my own Perl/Tk widgets
Perl/Tk’s option database
Tix widgets
Interprocess communication
Using C from Perl/Tk
If any of those topics interest you, or if you simply want the definitive Perl/Tk book, Mastering Perl/Tk is a natural next step.
If you’re determined to create applications without understanding what you’re doing, you can still get remarkably far by examining some of Steve’s programs (on both http://www.oreilly.com/catalog/mastperltk/ and http://www.oreilly.com/catalog/tpj2/) and the example programs bundled with the Perl/Tk distribution, finding one that approximates the behavior you need, and chopping out the code for behaviors you don’t.
To help you decide what you don’t need, Table 33-1 lists all the basic widgets, what they do, and what options they accept.
Widget | Purpose | Options |
Adjuster | Gives user control of widget size | Same as Frame plus -restore, -side, -delay, -widget |
Balloon | Displays text when mouse is positioned over a widget | Same as MainWindow plus -font, -balloonposition, -statusmsg, -postcommand, -installcolormap, -initwait, -state, -cancelcommand, -balloonmsg, -motioncommand, -statusbar |
Bitmap | Simple collection of pixels | -background, -data, -file, -foreground, -maskdata, -maskfile |
BrowseEntry | Drop-down listbox that lets user type entries | Same as Entry plus -labelHighlightcolor, -labelHeight, -labelOffset, -arrowimage, -label, -labelWraplength, -labelRelief, -labelPadx, -labelPady, -labelTextvariable, -labelJustify, -command, -labelHighlightbackground, -options, -labelFont, -labelVariable, -labelBackground, -listcmd, -labelImage, -labelTile, -labelActivetile, -listwidth, -variable, -labelCursor, -browsecmd, -labelTakefocus, -labelDisabledtile, -labelAnchor, -labelHighlightthickness, -labelText, -labelWidth, -colorstate, -labelPack, -labelForeground, -choices, -labelUnderline, -labelBitmap, -labelBorderwidth |
Button | Something the user presses to trigger an action | Same as Label plus -default, -state, -command, -disabledforeground, -activeforeground, -activeimage, -activebackground |
Canvas | A 2D area giving you pixel-by-pixel control | -activegroup, -background, -bd, -bg, -borderwidth, -closeenough, -confine, -cursor, -disabledtile, -height, -highlightbackground, -highlightcolor, -highlightthickness, -insertbackground, -insertborderwidth, -insertofftime, -insertontime, -insertwidth, -offset, -relief, -scrollregion, -selectbackground, -selectborderwidth, -selectforeground, -state, -takefocus, -tile, -width, -xscrollcommand, -xscrollincrement, -yscrollcommand, -yscrollincrement |
Checkbutton | A Button that the user can select or deselect | Same as Label plus -onvalue, -selectcolor, -variable, -offvalue, -state, -command, -disabledforeground, -activeforeground, -indicatoron, -selectimage, -activebackground |
ColorEditor | Lets user select colors | -background, -bd, -bg, -borderwidth, -class, -color, -color_space, -colormap, -command, -container, -cursor, -display_status, -fg, -foreground, -height, -highlight, -highlightbackground, -highlightcolor, -highlightthickness, -initialcolor, -offset, -overanchor, -popanchor, -popover, -relief, -takefocus, -tile, -title, -visual, -widgets, -width |
Dialog | Pop-up window for immediate user action | Same as Label plus -title, -overanchor, -command, -popover, -popanchor |
DirTree | HList tailored for | showing directories Same as HList plus -dircmd, -value, -image, -showhidden, -opencmd, -ignoreinvoke, -closecmd, -directory |
Entry | Lets users enter a little text | -background, -bd, -bg, -borderwidth, -cursor, -disabledtile, -exportselection, -fg, -font, -foreground, -fgtile, -foregroundtile, -highlightbackground, -highlightcolor, -highlightthickness, -insertbackground, -insertborderwidth, -insertofftime, -insertontime, -insertwidth, -invalidcommand, -invcmd, -justify, -offset, -relief, -selectbackground, -selectborderwidth, -selectforeground, -show, -state, -takefocus, -textvariable, -tile, -validate, -validatecommand, -vcmd, -width, -xscrollcommand |
ErrorDialog | Dialog for alerting user about application errors | -appendtraceback, -background, -bd, -bg, -borderwidth, -class, -cleanupcode, -colormap, -container, -cursor, -fg, -foreground, -height, -highlightbackground, -highlightcolor, -highlightthickness, -menu, -offset, -relief, -screen, -takefocus, -tile, -use, -visual, -width |
FileSelect | Listbox tailored for files | Same as Listbox plus -labelHighlightcolor, -resetlabel, -labelHeight, -labelOffset, -scrollbars, -homelabel, -verify, -defaultextension, -label, -labelWraplength, -labelRelief, -labelPadx, -labelPady, -labelTextvariable, -labelJustify, -command, -labelHighlightbackground, -filelabel, -labelFont, -labelVariable, -initialdir, -labelBackground, -create, -title, -labelImage, -transient, -labelTile, -labelActivetile, -cancellabel, -filter, -labelCursor, -acceptlabel, -labelTakefocus, -overanchor, -labelDisabledtile, -dirlabel, -labelAnchor, -labelHighlightthickness, -labelText, -labelWidth, -regexp, -dirlistlabel, -labelPack, -initialfile, -accept, -directory, -labelForeground, -popover, -popanchor, -labelUnderline, -labelBitmap, -labelBorderwidth, -filelistlabel |
Frame | Container for other widgets | -background, -bd, -bg, -borderwidth, -class, -colormap, -container, -cursor, -fg, -foreground, -height, -highlightbackground, -highlightcolor, -highlightthickness, -label, -labelPack, -labelVariable, -offset, -relief, -takefocus, -tile, -visual, -width |
HList | Hierarchical list | -background, -bd, -bg, -borderwidth, -browsecmd, -columns, -command, -cursor, -dragcmd, -drawbranch, -dropcmd, -exportselection, -fg, -font, -foreground, -gap, -header, -height, -highlightbackground, -highlightcolor, -highlightthickness, -indent, -indicator, -indicatorcmd, -itemtype, -padx, -pady, -relief, -selectbackground, -selectborderwidth, -selectforeground, -selectmode, -separator, -sizecmd, -takefocus, -wideselection, -width, -xscrollcommand, -yscrollcommand |
Label | Noninteractive widget displaying an image or text | -activetile, -anchor, -background, -bd, -bg, -bitmap, -borderwidth, -cursor, -disabledtile, -fg, -font, -foreground, -height, -highlightbackground, -highlightcolor, -highlightthickness, -image, -justify, -offset, -padx, -pady, -relief, -takefocus, -text, -textvariable, -tile, -underline, -width, -wraplength |
LabEntry | An Entry with a Label | Same as Entry plus -label, -labelPack, -labelVariable |
LabFrame | A Frame with a Label | Same as Frame, plus -labelside |
Listbox | List of text strings | -background, -bd, -bg, -borderwidth, -cursor, -exportselection, -fg, -font, -foreground, -height, -highlightbackground, -highlightcolor, -highlightthickness, -offset, -relief, -selectbackground, -selectborderwidth, -selectforeground, -selectmode, -setgrid, -takefocus, -tile, -width, -xscrollcommand, -yscrollcommand |
MainWindow | TopLevel widget displayed by MainLoop | -background, -bd, -bg, -borderwidth, -class, -colormap, -container, -cursor, -fg, -foreground, -height, -highlightbackground, -highlightcolor, -highlightthickness, -menu, -offset, -overanchor, -popanchor, -popover, -relief, -screen, -takefocus, -tile, -title, -use, -visual, -width |
Menu | Emergent window displaying menu items | -activebackground, -activeborderwidth, -activeforeground, -activetile, -background, -bd, -bg, -borderwidth, -cursor, -disabledforeground, -disabledtile, -fg, -font, -foreground, -offset, -overanchor, -popanchor, -popover, -postcommand, -relief, -selectcolor, -takefocus, -tearoff, -tearoffcommand, -tile, -title, -type |
Menubutton | Individual menu items | Same as Label plus -menu, -state, -disabledforeground, -direction, -activeforeground, -indicatoron, -activebackground |
Message | Displays message for user | -anchor, -aspect, -background, -bd, -bg, -borderwidth, -cursor, -fg, -font, -foreground, -highlightbackground, -highlightcolor, -highlightthickness, -justify, -padx, -pady, -relief, -takefocus, -text, -textvariable, -tile, -width |
NoteBook | Groups tabbed windows together | -background, -backpagecolor, -bd, -bg, -borderwidth, -cursor, -disabledforeground, -dynamicgeometry, -fg, -focuscolor, -font, -foreground, -inactivebackground, -ipadx, -ipady, -relief, -slave, -tabpadx, -tabpady, -takefocus, -width |
Optionmenu | Menu offering the user many mutually exclusive options | Same as Menubutton plus -variable, -command, -options |
Pane | A scrollable Frame | Same as Frame plus -sticky, -xscrollcommand, -gridded, -yscrollcommand |
Photo | Holds an image | -data, -format, -file, -gamma, -height, -palette, -width |
ProgressBar | Shows user the “percentage complete” | Same as Canvas plus -colors, -troughcolor, -value, -to, -blocks, -variable, -foreground, -from, -length, -resolution, -fg, -gap, -anchor, -padx, -pady |
Radiobutton | A Button that, when selected, deselects the rest in the group | Same as Label plus -value, -selectcolor, -variable, -state, -command, -disabledforeground, -activeforeground, -indicatoron, -selectimage, -activebackground |
ROText | Text widget, read-only | Same as Text |
Scale | Slider for controlling a number | -activebackground, -activetile, -background, -bigincrement, -bd, -bg, -borderwidth, -command, -cursor, -digits, -fg, -disabledtile, -font, -foreground, -from, -highlightbackground, -highlightcolor, -highlightthickness, -label, -length, -offset, -orient, -relief, -repeatdelay, -repeatinterval, -resolution, -showvalue, -sliderlength, -sliderrelief, -state, -takefocus, -tickinterval, -tile, -to, -troughcolor, -troughtile, -variable, -width |
Scrollbar | Slider for moving a widget horizontally or vertically | -activebackground, -activerelief, -activetile, -background, -bd, -bg, -borderwidth, -command, -cursor, -elementborderwidth, -highlightbackground, -highlightcolor, -highlightthickness, -jump, -orient, -relief, -repeatdelay, -repeatinterval, -takefocus, -tile, -offset, -troughcolor, -troughtile, -width |
Table | Displays a table of items | Same as Frame plus -rows, -scrollbars, -fixedcolumns, -fixedrows, -columns |
Text | Displays text, editable by user | -background, -bd, -bg, -borderwidth, -cursor, -disabledtile, -exportselection, -fg, -font, -foreground, -height, -highlightbackground, -highlightcolor, -highlightthickness, -insertbackground, -insertborderwidth, -insertofftime, -insertontime, -insertwidth, -offset, -padx, -pady, -relief, -selectbackground, -selectborderwidth, -selectforeground, -setgrid, -spacing1, -spacing2, -spacing3, -state, -tabs, -takefocus, -tile, -width, -wrap, -xscrollcommand, -yscrollcommand |
TextUndo | Text widget suited for writing documents | Same as Text |
Tiler | A Frame of matrix cells | Same as Frame plus -rows, -columns, -yscrollcommand |
TList | Text list | -background, -bd, -bg, -highlightbackground, -borderwidth, -browsecmd, -command, -cursor, -fg, -font, -foreground, -height, -highlightcolor, -highlightthickness, -itemtype, -orient, -padx, -pady, -relief, -selectbackground, -selectborderwidth, -selectforeground, -selectmode, -state, -sizecmd, -takefocus, -width, -xscrollcommand, -yscrollcommand |
Toplevel | Decorated container for other widgets | Same as MainWindow |
Tree | HList that lets user open and close portions | Same as HList plus -opencmd, -ignoreinvoke, -closecmd |
In the next article, Getting Started with Perl/Tk, Steve provides a gentle introduction to show you what some simple Perl/Tk programs look like.