A combobox appears to be an entry box which has associated with it a series of possible values, along with a button (with a down arrow) that, when pressed, displays the various options that can be selected for the entry box.
The combobox widget shipped with tk8.5 is ttk::combobox. Besides this native widget, there's a wealth of additional implementations available. Bryan Oakley's is pure-Tcl, widely used, and maintained efficiently. BWidgets is a popular pure-Tcl widget set [in Batteries Included distributions?] with an excellent combobox. [... List others, including Donal Fellows', the Iwidgets one, the one in Tix, ...]
What: ComboBox (jay) Where: From the contact Description: Tk combo box code. Updated: Contact: mailto:[email protected] (jay) What: ComboBox (Joglekar) Where: ftp://ftp.tcl.tk/pub/tcl/mirror/ftp.procplace.com/sorted/packages-7.6/devel/graphics/ComboBox.tar.gz Description: Tk 4.0 code to implement a basic ComboBox widget. Updated: 10/1998 Contact: mailto:[email protected] (Ashutosh Joglekar) What: Combobox (Oakley) Where: ycl (with updates, 2012-12-30) Where: http://purl.oclc.org/net/oakley/tcl/combobox/ Where: http://www2.clearlight.com/~oakley/tcl/combobox/index.html Description: Tcl/Tk 8.0 or better based, tcl only, combobox. All the code is in one file, with an API similar to the standard Tk widgets (with subcommands such as configure, cget, insert etc). Emulates the look and feel of a Windows combobox. Supports all platforms supported by Tcl 8.x. Recommended used with Tcl 8.x. New versions continue to appear above - check to see if a new release with bug fixes and features is available. Updated: 04/1999 Contact: mailto:[email protected] (Bryan Oakley) What: HugeCombo package Where: https://wiki.tcl-lang.org/_repo/ulis/Hugecombo.zip Description: a(Huge)ComboBox is a pure Tcl megawidget replacing the entry widget of Tk 8.4. It augments the entry widget with a pick-list and its calling-button. This pick-list is the famous Hugelist which allows to choose among more than 1,000,000 items without time or memory penalty. The search is based on the string match patterns. Updated: 2003-10-31 Contact: ulis Screenshot: What: MegaWidget package What: Miscellaneous Tcl procs (Corey) Where: http://www.kencorey.com/tcl/answers.html Description: Examples of how to do things like provide balloon help over menu items, do background processing, eat events while a program is busy, do combobox widgets, scroll two text widgets with one scrollbar, scroll to currently focused canvas item, moving graphs, move the nodes of a polygon around dynamically, track what procedures are called (with what arguments), scrolling a grid managed frame in a canvas, using fileevent on a pipe, simple spreadsheet using grid, and a simple listbox inside a text widget. The contact is currently not updating this page. Updated: 08/1998 Contact: mailto:[email protected] (Ken Corey) What: PRS Open Source Software What: TinyCombo package Where: https://wiki.tcl-lang.org/_repo/ulis/Tinycombo.zip Description: a(Tiny)ComboBox is a pure Tcl megawidget replacing the entry widget of Tk 8.4. It augments the entry widget with a pick-list and its calling-button. This pick-list is not the famous Hugelist but the standard Tk listbox. The search is based on the string match patterns. Updated: 2003-02-02 Contact: ulis Screenshot:
The Tix combobox documentation can be found at http://tix.sourceforge.net/man/html/TixCmd/tixComboBox.htm .
Docs for incr Widgets combobox can be found at http://incrtcl.sourceforge.net/iwidgets/iwidgets/combobox.html and http://purl.org/tcl/home/man/iwidgets3.0/combobox.n.html
RS: In Enhancing BWidget is demonstrated how to extend the behavior of BWidget's comboboxes, to add a history of previous input; or to make them look like a chooser (somehow like the tk_optionMenu, which also is a kind of combo, but looks kind of old-fashioned these days).