TIP #306 Version 1.3: Auto-Naming Widgets

This is not necessarily the current version of this TIP.

Abstract

A Tk programmer must give every widget a unique name. This is often quite annoying, especially for widgets whose name is stored in a variable (which also must be given a name). This TIP proposes a small extension to generate automatic names for widgets.

Rationale

Every Tk widget must be given a unique name. This is needed internally for Tk and also for the programmer to be able to refer to it. Quite often, and as recommended in many Tk coding guidelines (e.g. http://www.beedub.com/book/2nd/TKINTRO.doc.html), the widget names are stored in variables and only referred to indirectly. These variables must also be given a name, which may lead to confusion, and requires more inventivity of the programmer than needed.

An example from the BWidget source code:

 set status   [frame $path.status -background $bg]
 set label    [label $status.label]
 set indframe [frame $status.indf -background $bg]
 set prgframe [frame $status.prgf -background $bg]

Other cases where widget names are unimportant from a programmer's viewpoint, are widgets which are never referred to after creation, and those which are only referred to by other means (e.g. by a textvariable). Example:

 pack [label .name_label -text "Enter name:"] -side left
 pack [entry .name_entry -textvariable name] -side left

In all those cases, it would be helpful if Tk could generate the widget names itself.

Currently the widget creation commands already return the widget name, which is always the exact name the programmer has supplied. This makes it easy to make an (almost) backwards compatible extension, as presented below.

Specification

When creating a new widget with a name that ends on "%", the "%" will be replaced by a counter. The actual widget name is then returned. Note that each parent widget has its own counter.

 % button .%
 .1
 % set f [frame .%]
 .2
 % label $f.%
 .2.1
 % set p [frame .prefix%]
 .prefix3
 % label $p.%a%b%c%%
 .prefix3.%a%b%c%1

The examples above can now be written as:

 set status   [frame $path.% -background $bg]
 set label    [label $status.%]
 set indframe [frame $status.% -background $bg]
 set prgframe [frame $status.% -background $bg]

 pack [label .% -text "Enter name:"] -side left
 pack [entry .% -textvariable name] -side left

Note that there is no protection against already existing window names. Example:

 % frame .2
 .2
 % frame .%
 .1
 % frame .%
 window name "2" already exists in parent

Reference Implementation

[To come soon]

Basically, the TkWindow structure gets a new member "autocount", which is initalized to 0 when the widget is created, and which is incremented when the auto-name feature is used for creating child widgets (this is done in the NameWindow() function).