# Tix Frequently Asked Questions

### Legal Issues

[L.1] Is Tix free software?

  ANSWER: Tix is distributed under the same license as Tcl/Tk (a.k.a. BSD style license). Application developers can freely redistribute Tix along with their products.

### General Questions About Using The Tix Library

[G.1] What does the "`-disablecallback`" option do?

  ANSWER: Many Tix widgets have both a `-value` option and a `-command` option. Any modification of the `-value` will cause the `-command` callback to be executed. Sometimes this is undesirable. For example, calling "`config -value`" inside the callback procedure will cause the callback to be re-entered and thus an infinite recursion.

  The `-disablecallback` can be used to advoid this problem. When this option is set, the `-command` callback will not be executed even if the -value of a widget is changed. Therefore, if you need to modify the -value of a widget inside its callback, do this:

  >         proc my_callback {w} {
  >     	$w config -disablecallback true
  >     	$w config value blah
  >     	$w config -disablecallback false
  >         }

  If you find this too troublesome, you can call the command tixSetSilent:

  >         proc my_callback {w} {
  >     	tixSetSilent $w blah
  >         }

[G.2] How do I set the width of the entry subwidget inside the tixControl widget?

  ANSWER: You can use the option database or the -options flag to set the configuration options of the subwidgets. E.g:

      option add *TixControl*entry.width 10

  OR

      tixControl .c -options {
         entry.width  10
      }

[G.6] I am not using the tixForm geometry manager, but it is giving me errors about TixForm. What happened?

  ANSWER: When you get error messages like this:

       (TixForm) Error:Trying to use more than one geometry
                 manager for the same master window.
                 Giving up after 50 iterations.

  Most likely, the problem is when using tixLabelFrame widgets, you packed to the wrong frame:

  This is WRONG:

         tixLabelFrame .d
              button .d.b
              pack .d.b

  This is the correct way:

         tixLabelFrame .d
              set f [.d subwidget frame]
              button $f.b
              pack $f.b
              pack .d

  Remember you don't pack directly into a TixLabelFrame widget. Instead, you should pack into its `frame` subwidget.

[G.7] How do I generate the `tclIndex` file for Tix?

  ANSWER: Tix `tclIndex` files cannot be generated using the standard auto_mkindex procedure. You must use the tixindex program in the `tools/` subdirectory in the Tix distribution. The syntax is

       tixindex *.tcl

[G.8] Can I ignore the default arguments passed by the various `-command` and `-browsecmd` options?

  ANSWER: You can use the `tixBreak` command. For example:

       tixFileSelectDialog .c -command "puts foo; tixBreak"

[G.9] What does `tixWidgetDoWhenIdle` do?

  ANSWER: It does the same thing as tixDoWhileIdle (and "after -idle"). The difference is it takes its second argument as the name of a widget and executes this command only if the widget exists: i.e.:

        tixWidgetDoWhenIdle tixComboBox::Update $w blah blah ..

  will execute tixComboBox::Update only if $w exists. $w may be destroyed after tixWidgetDoWhenIdle is called but before an idle event happens.

[G.10] Why isn't such a feature in Tix? Will it be implemented?

  ANSWER: Generally requests for new features are welcomed. You can submit your requests to http://tix.sourceforge.net and we'll be happy to hear from you.

  We can't guarantee to implement the requested features immediately. Usually it depends on how important the features. If the feature is requested by more people, it will usually get done faster. However, some frequently requested features probably won't be imlemented. Usually these features are cosmetic changes and:

  - they do not add new capability to the widgets
  - they are not universally liked
  - they confuse the user.

  Some examples are:

  - Different foreground and background colors for the NoteBook tabs: having a lot of colors may antagonize the users that are "color haters"; also, the different colors don't make it easier for the user to locate the desired tab.
  - Ring-binder metaphore for the NoteBook widget: a waste of screen real estate.
  - Rows of tabs for the NoteBook widget: the user may be confused when the rows of tabs are switched. If you need to have a lot of tabs for the notebook, use the ListNoteBook widget instead.

[G.11] Who are using Tix in their software?

  ANSWER: See http://tix.sourceforge.net

[G.12] I am using a DirList widget. When the user clicks on an item, the procedure of my `-browsecmd` gets called twice. However, I just want it to be called once.

  ANSWER: The `-browsecmd` procedure is triggered by three types of events: `<1>`, `<ButtonRelease-1>`, and `<B1-Motion>`. When the user clicks on an entry, a `<1>` and a `<ButtonRelease-1>` event will happen in rapid session, which causes your `-browsecmd` procedure to be called twice.

  A crude fix for this problem is to ignore all the `<ButtonRelease-1>` events. You can find out the event that triggers the `-browsecmd` procedure by the `tixEvent` command. Here is an example:

  >         tixDirList .c -browsecmd Browse

  >         proc Browse {args} {
  >     	if {[tixEvent type] == "<ButtonRelease-1>"} {
  >     	    return
  >     	}
  >     	# ....
  >         }

  However, the above solution is not perfect. For example, if the user clicks down the button at entry one, drags it over entries two and three and release it on top of entry three, the following events may be caused:

  1. `<1>` on entry one.
  2. `<B1-Motion>` on entry two.
  3. `<ButtonRelease-1>` on entry three.

  Therefore, if you use the above method, the browse event on entry three will be lost!

  To devise a better solution, it's better to understand the basic design conventions of a Tix-based GUI. Suppose we have a list of entries displayed in a listbox (or DirList, or HList). When the user clicks on an entry, the GUI usually responds by displaying a "detailed view" of the entry. For example, if we put a list of file names in a listbox, when the user clicks on a file name, we display the contents of the file in a text window. If the user then clicks on another file name, the text window will load in the contents of the new file.

  Now what happens if the user clicks on the same entry twice? Do we reload the contents of the file into the text window? This is usually unnecessary, inefficient and probably not what the user wants to do. The Tix convention is, when the user clicks on the same entry again, the detail view is not updated. If the user wants to force an update (e.g, the user knows the file's contents has been changed and wants to see the new version), he or she can double-click on the entry and the application will respond by redisplaying the detail view (reloading the file).

  To implement this policy, the Browse procedure should be modified as the following:

  >         proc Browse {args} {
  >     	global currentView

  >     	set ent [tixEvent value]
  >     	if {$ent == $currentView} {
  >     	    # We have already displayed the detailed view of $ent.
  >     	    #
  >     	    return
  >     	} else {
  >     	    set currentView $ent
  >     	    DisplayDetail $ent
  >     	}
  >         }

[G.13] I get an error "can't read data(-value): no such element in array" when I use the tixExFileSelectDialog.

  ANSWER: If you use tixExFileSelectDialog like this:

      	tixExFileSelectDialog .f -command foo

      	foo {filename} {
      	    destroy .f
      	    do some other stuff ...
      	}

  it will cause a Tcl error because the dialog assumes that it still exists after calling your command. This usually result in errors like this:

      	can't read "data(-value)": no such element in array
      	    while executing
      	"set data(-selection) $data(-value)..."
      	    (procedure "tixComboBox::SetValue" line 30)

  This "feature" is built into many Tix widgets and can't be fixed easily. To work around the problem, never destroy widgets inside -command calls. Usually you should unmap toplevel windows instead. If you must destroy widgets, do it with an "after" command. For example, the foo procedure should be rewritten as:

      	foo {filename} {
      	    wm withdraw .f
      	    do some other stuff ...

      	    after idle {if [winfo exists .f] {destroy .f}}
      	}

  Execute the "after" command at the very end of the -command. Otherwise the idle handler may be activated by some "update" calls.

### Question About Porting to Specific Platforms/Software

[P.1] The configure script gave me strange errors.

  ANSWER: The problem may be you have several operating systems sharing the same file system. Some people encounter error messages like this:

  >     # ./configure --prefix=/usr/vendor/tcl
  >     loading cache ./config.cache
  >     checking for a BSD compatible install... /usr/bin/installbsd -c
  >     checking for ranlib... ranlib
  >     checking how to run the C preprocessor... cc -E
  >     checking for unistd.h... ./configure[603]: "${ac_cv_header_$ac_safe+set}": bad
  >     substitution

  The problem is at line 2, configure loaded in ./config.cache, which may have been created by a different operating system, with settings only usuable for that operating system. To get around this, you should type

  >     make distclean
  >     ./configure
  >     make all