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Initial import of the CDE 2.1.30 sources from the Open Group.

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<!-- $XConsortium: ch01.sgm /main/7 1996/09/08 19:45:34 rws $ -->
<!-- (c) Copyright 1995 Digital Equipment Corporation. -->
<!-- (c) Copyright 1995 Hewlett-Packard Company. -->
<!-- (c) Copyright 1995 International Business Machines Corp. -->
<!-- (c) Copyright 1995 Sun Microsystems, Inc. -->
<!-- (c) Copyright 1995 Novell, Inc. -->
<!-- (c) Copyright 1995 FUJITSU LIMITED. -->
<!-- (c) Copyright 1995 Hitachi. -->
<chapter id="DKSUG.Intro.div.1">
<title id="DKSUG.Intro.mkr.1">Introduction to Desktop KornShell</title>
<para>Desktop KornShell(<command>ldtksh<indexterm><primary>dtksh</primary>
<secondary>definition</secondary></indexterm></command>) provides kshell scripts
with the means for easily accessing most of the existing Xt and Motif&trade;
functions. <command>dtksh</command> is based on <filename>ksh-93<indexterm>
<primary>dtksh</primary><secondary>relationshipt to ksh-93</secondary></indexterm><indexterm>
<primary>ksh-93</primary></indexterm></filename>, which provides a powerful
set of tools and commands for the shell programmer, and which supports the
standard set of kshell programming commands.</para>
<para><command>dtksh</command> supports all the features and commands provided
by <filename>ksh-93</filename>. In addition, <command>dtksh</command> supports
a large selection of the <command>libDt</command> functions, most of the
widget-related Motif functions, a large subset of the Xt Intrinsics functions,
and a small subset of the Xlib functions. All the supported functions are
listed in Appendix A.<indexterm><primary>supported functions</primary></indexterm><indexterm>
<primary>functions</primary><secondary>supported</secondary></indexterm></para>
<sect1 id="DKSUG.Intro.div.2">
<title>Using Desktop KornShell to Create Motif Applications</title>
<para>This section describes how to use <command>dtksh</command> to create<indexterm><primary>Motif applications</primary></indexterm>
Motif<indexterm>
<primary>applications, Motif</primary></indexterm> applications. To successfully
use <command>dtksh</command>, you should have experience with Xlib, the Xt
Intrinsics, the Motif widgets, and KornShell programming. It is also helpful
to know the C programming language. If you are not familiar with any of
these, you should refer to the appropriate documentation. Even if you are
familiar with these systems, you should have access to the applicable man
pages for reference.</para>
<para>In addition, your system should have these libraries:<indexterm><primary>required linbraries</primary></indexterm><indexterm><primary>libraries, required</primary></indexterm></para>
<itemizedlist remap="Bullet1"><listitem><para><command>libDtHelp</command></para>
</listitem><listitem><para><command>libDtSvc</command></para>
</listitem><listitem><para><command>libX11</command></para>
</listitem><listitem><para><command>libXm</command></para>
</listitem><listitem><para><command>libXt</command></para>
</listitem><listitem><para><command>libtt</command></para>
</listitem></itemizedlist>
<sect2 id="DKSUG.Intro.div.3">
<title>Resources<indexterm><primary>resources</primary></indexterm></title>
<para>Resources are widget variables that you use to define attributes such
as size, location, or color. Each widget usually has a combination of its
own resources, plus resources it inherits from higher level widgets. Xt
Intrinsics and Motif resource names consist of a prefix (<command>XtN</command>
or <command>XmN</command>) followed by the base name. The first letter of
the base name is <emphasis>always</emphasis> lowercase, and the first letter
of subsequent words within the base name is <emphasis>always</emphasis> uppercase.
The convention for resource names in <command>dtksh</command> scripts is
to delete the prefix and use the base name. Thus, the resource <command>XmNtopShadowColor</command> becomes <command>topShadowColor</command>.<indexterm>
<primary>XmNtopShadowColor</primary></indexterm><indexterm><primary>topShadowColor</primary></indexterm></para>
<para>Some Xt and Motif commands allow the shell script to pass in a variable
number of<indexterm><primary>parameters, variable number</primary></indexterm> parameters,
representing resource-value pairs. This is similar to the argument list passed
to the corresponding Xt or Motif C function. Examples include any of the
commands used to create a widget, plus the <command>XtSetValues</command>
command. In <command>dtksh</command>, resources are specified by a string
with the following syntax:</para>
<programlisting>resource:<symbol role="Variable">value</symbol></programlisting>
<para>where <symbol role="Variable">resource</symbol> is the name of the resource
and <symbol role="Variable">value</symbol> is the value assigned to the resource.
<command>dtksh</command> automatically converts the <symbol role="Variable">value</symbol> string to an appropriate internal representation. For example:
</para>
<programlisting>XtSetValues $WIDGET height:100 width:200 resizePolicy:RESIZE_ANY
XmCreateLabel LABEL $PARENT myLabel labelString:&rdquo;Close Dialog&rdquo;
</programlisting>
<para>When you retrieve widget resource values using <command><indexterm>
<primary>XtGetValues</primary></indexterm>XtGetValues</command>, the return
value is placed in an environment variable. Thus, unlike the Xt Intrinsics,
the <command>dtksh</command> version of <command>XtGetValues</command> uses
a name:(environment) variable pair, rather than a name:value pair. For example:
</para>
<programlisting>XtGetValues $WIDGET height:HEIGHT resizePolicy:POLICY
sensitive:SENSITIVE
echo $HEIGHT
echo $POLICY
echo $SENSITIVE</programlisting>
<para>The preceding <command>dtksh</command> segment might produce this output:
</para>
<programlisting>100
RESIZE ANY
TRUE</programlisting>
<para>Certain types of resource values, including string tables and bit masks,
have special representation. For example, the List widget allows a string
table to be specified for both the <command>items</command> and <command>selectedItems</command> resources. In <command>dtksh</command>, a string
table is represented as a comma-separated list of strings, which is similar
to how Motif treats them. When a resource that returns a string table is
queried using <command>XtGetValues<indexterm><primary>XtGetValues</primary>
</indexterm></command>, the resulting value is a comma-separated set of strings.
</para>
<para>A resource that expects a bit mask value to be passed to it expects
the mask to be specified as a string composed of the various mask values
separated by the |(bar) character. When a resource that returns a bit mask
is queried, the return value is a string representing the enabled bits, separated
by the | character. For example, you could use the following command to set
the <command><indexterm><primary>mwmFunctions</primary></indexterm><indexterm>
<primary>VendorShell</primary></indexterm>mwmFunctions</command> resource
for the <command>VendorShell</command> widget class:</para>
<programlisting>XtSetValues mwmFunctions: MWM_FUNC_ALL|MWM_FUNC_RESIZE</programlisting>
</sect2>
<sect2 id="DKSUG.Intro.div.4">
<title>Unsupported Resources<indexterm><primary>unsupported resources</primary>
</indexterm><indexterm><primary>resource</primary><secondary>unsupported</secondary></indexterm></title>
<para><command>dtksh</command> supports most of the Motif resources. The
following lists unsupported resources. Resources with an * (asterisk) can
be specified at widget creation time by using <command><indexterm><primary>XtSetValues</primary></indexterm>XtSetValues</command>, but can't be retrieved
using <command><indexterm><primary>XtGetValues</primary></indexterm>XtGetValues</command>.</para>
<itemizedlist remap="Bullet1"><listitem><para>All widget and gadget Classes:
</para>
<itemizedlist remap="Bullet2"><listitem><para>Any fontlist resource *</para>
</listitem><listitem><para>Any pixmap resource *</para>
</listitem></itemizedlist>
</listitem><listitem><para>Composite:</para>
<itemizedlist remap="Bullet2"><listitem><para><command>insertPosition</command></para>
</listitem><listitem><para><command>children</command></para>
</listitem></itemizedlist>
</listitem><listitem><para>Core:</para>
<itemizedlist remap="Bullet2"><listitem><para><command>accelerators</command></para>
</listitem><listitem><para><command>translations</command> *</para>
</listitem><listitem><para><command>colormap</command></para>
</listitem></itemizedlist>
</listitem><listitem><para><command>XmText</command>:</para>
<itemizedlist remap="Bullet2"><listitem><para><command>selectionArray</command></para>
</listitem><listitem><para><command>selectionArrayCount</command></para>
</listitem></itemizedlist>
</listitem><listitem><para><command>ApplicationShell</command>:</para>
<itemizedlist remap="Bullet2"><listitem><para><command>argv</command></para>
</listitem></itemizedlist>
</listitem><listitem><para><command>WMShell</command>:</para>
<itemizedlist remap="Bullet2"><listitem><para><command>iconWindow</command></para>
</listitem><listitem><para><command>windowGroup</command></para>
</listitem></itemizedlist>
</listitem><listitem><para><command>Shell</command>:</para>
<itemizedlist remap="Bullet2"><listitem><para><command>createPopupChildrenProc</command></para>
</listitem></itemizedlist>
</listitem><listitem><para><command>XmSelectionBox</command>:</para>
<itemizedlist remap="Bullet2"><listitem><para><command>textAccelerators</command></para>
</listitem></itemizedlist>
</listitem><listitem><para><command>Manager</command>, <command>Primitive</command>, and <command>Gadget</command> Subclasses:</para>
<itemizedlist remap="Bullet2"><listitem><para><command>userData</command></para>
</listitem></itemizedlist>
</listitem><listitem><para><command>XmFileSelectionBox</command>:</para>
<itemizedlist remap="Bullet2"><listitem><para><command>dirSearchProc</command></para>
</listitem><listitem><para><command>fileSearchProc</command></para>
</listitem><listitem><para><command>qualifySearchDataProc</command></para>
</listitem></itemizedlist>
</listitem></itemizedlist>
</sect2>
<sect2 id="DKSUG.Intro.div.5">
<title>dtksh app-defaults File<indexterm><primary>app-defaults file</primary>
</indexterm></title>
<para>The <command>dtksh</command> <filename>app-defaults</filename> file,
named <command>Dtksh</command><indexterm><primary>Dtksh, app-defaults file</primary></indexterm>, is found in a location based on the following path
description:</para>
<programlisting>/usr/dt/app-defaults/&lt;LANG></programlisting>
<para>The only information contained in this <filename>app-defaults</filename>
file is the inclusion of the standard <command>Dt</command> base
<filename>app-defaults</filename> file. The following is a listing of the <command>dtksh</command> <filename>app-defaults</filename> file:</para>
<programlisting>#include &ldquo;Dt&ldquo;</programlisting>
<para>The file <command>Dt</command> is also located in <computeroutput>/usr/dt/app-defaults/&lt;LANG></computeroutput> and is shown in the following listing.</para>
<programlisting>*foregroundThreshold: 70
!###
!#
!# Help system specific resources
!#
!###
!#
!# Display Area Colors
!#
!# These resources set the colors for the display area (where
!# actual help text is displayed). The resources are complex
!# because they have to override the standard color resources
!# in all cases.
!#
*XmDialogShell.DtHelpDialog*DisplayArea.background: White
*XmDialogShell*XmDialogShell.DtHelpDialog*DisplayArea.background:
White
*XmDialogShell.DtHelpDialog*DisplayArea.foreground: Black
*XmDialogShell*XmDialogShell.DtHelpDialog*DisplayArea.foreground:
Black
!#
!# Menu Accelerators
!#
!# The following resources establish keyboard accelerators
!# for the most frequently accessed menu commands.
!#
*DtHelpDialogWidget*searchMenu.keyword.acceleratorText: Ctrl+I
*DtHelpDialogWidget*searchMenu.keyword.accelerator: Ctrl&lt;Key>i
*DtHelpDialogWidget*navigateMenu.backTrack.acceleratorText: Ctrl+B
*DtHelpDialogWidget*navigateMenu.backTrack.accelerator: Ctrl&lt;Key>b
*DtHelpDialogWidget*navigateMenu.homeTopic.acceleratorText: Ctrl+H
*DtHelpDialogWidget*navigateMenu.homeTopic.accelerator: Ctrl&lt;Key>h
*DtHelpDialogWidget*fileMenu.close.acceleratorText: Alt+F4
*DtHelpDialogWidget*fileMenu.close.accelerator: Alt&lt;Key>f4</programlisting>
</sect2>
<sect2 id="DKSUG.Intro.div.6">
<title>Variable Values<indexterm><primary>variable values</primary></indexterm></title>
<para>This section describes the types of values for some of the variables
in a <command>dtksh</command> <filename>app-defaults</filename> file.</para>
<sect3 id="DKSUG.Intro.div.7">
<title>Defined Values<indexterm><primary>Defined Values</primary></indexterm></title>
<para>The C bindings of the interfaces to X, Xt and Motif include many nonstring
values that are defined in header files. The general format of such values
consists of an <command>Xt</command> or <command>Xm</command> prefix followed
by a descriptive name. For example, one of the constraint values for a child
of a form widget is <filename>XmATTACH_FORM</filename>. Equivalent values
are specified in <command>dtksh</command> by dropping the prefix, just as
in a Motif defaults file:</para>
<itemizedlist remap="Bullet1"><listitem><para><filename>XmDIALOG_COMMAND_TEXT</filename>
becomes <filename>DIALOG_COMMAND_TEXT</filename></para>
</listitem><listitem><para><filename>XtATTACH_FORM</filename>
becomes <filename>ATTACH_FORM</filename></para>
</listitem></itemizedlist>
</sect3>
<sect3 id="DKSUG.Intro.div.8">
<title>Boolean Values<indexterm><primary>Boolean Values</primary></indexterm></title>
<para>You can specify a Boolean value as a parameter to a <command>dtksh</command>
command using the words True or False; case is not significant. A Boolean
result is returned as either True or False, using all lowercase letters.
</para>
</sect3>
</sect2>
<sect2 id="DKSUG.Intro.div.9">
<title>Return Values<indexterm><primary>Return Values</primary></indexterm></title>
<para>Graphical commands in <command>dtksh</command> fall into one of four
categories, based on the definition of the corresponding C function:</para>
<orderedlist><listitem><para>The function is void and returns no values.
Example: <filename>XtMapWidget()</filename></para>
</listitem><listitem><para>The function is void, but returns one or more values
through reference parameters. Example: <filename>XmGetColors()</filename></para>
</listitem><listitem><para>The function returns a non-Boolean value. Example:
<filename>XtCreateManagedWidget()</filename></para>
</listitem><listitem><para>The function returns a Boolean value. Example:
<filename>XtIsSensitive()</filename></para>
</listitem></orderedlist>
<sect3 id="DKSUG.Intro.div.10">
<title>Category 1<indexterm><primary>return value</primary><secondary>category
1</secondary></indexterm></title>
<para>A <command>dtksh</command><indexterm><primary>category 1</primary>
</indexterm> category 1 command follows the calling sequence of its corresponding
C function. The number and order of parameters can be determined by looking
at the standard documentation for the function. Example:</para>
<programlisting>XtMapWidget $FORM
</programlisting>
</sect3>
<sect3 id="DKSUG.Intro.div.11">
<title>Category 2<indexterm><primary>return value</primary><secondary>category
2</secondary></indexterm></title>
<para>A <command>dtksh</command><indexterm><primary>category 2</primary>
</indexterm> category 2 command also generally follows the calling sequence
of its corresponding C function. It returns a value in an environment variable,
instead of passing a pointer to a return variable. Example:</para>
<programlisting>XmGetColors $FORM $BG FOREGROUND TOPSHADOW BOTTOMSHADOW SELECT
echo &ldquo;Foreground color = &ldquo; $FOREGROUND</programlisting>
</sect3>
<sect3 id="DKSUG.Intro.div.12">
<title>Category 3<indexterm><primary>return value</primary><secondary>category
3</secondary></indexterm></title>
<para>A <command>dtksh</command><indexterm><primary>category 3</primary>
</indexterm> category 3 command differs slightly from its corresponding C
function. Where the C function returns its value as the value of the procedure
call, a <command>dtksh</command> command requires an additional parameter.
This parameter is the name of an environment variable into which the return
value is to be placed. It is always the first parameter. Example:
</para>
<programlisting>XmTextGetString TEXT_VALUE $TEXT_WIDGET
echo &ldquo;The value of the text field is &ldquo;$TEXT_VALUE</programlisting>
</sect3>
<sect3 id="DKSUG.Intro.div.13">
<title>Category 4<indexterm><primary>return value</primary><secondary>category
4</secondary></indexterm></title>
<para>A <command>dtksh</command><indexterm><primary>category 4</primary>
</indexterm> category 4 command returns a value that can be used in a conditional
expression just as in C. If the C function also returns values through reference
variables (as in category 2), the <command>dtksh</command> command also uses
variable names for the corresponding parameters. Example:</para>
<programlisting>if XmIsTraversable $PUSH_BUTTON; then
echo &ldquo;The pushbutton is traversable&rdquo;
else
echo &ldquo;The pushbutton is not traversable&rdquo;
fi</programlisting>
<para>Generally, the order and type of parameters passed to a command matches
those passed to the corresponding C function, except as noted for category
3 commands.</para>
</sect3>
</sect2>
<sect2 id="DKSUG.Intro.div.14">
<title>Immediate Return Value<indexterm><primary>return value</primary><secondary>immediate</secondary></indexterm><indexterm><primary>immediate return value</primary></indexterm></title>
<para>Many of the<indexterm><primary>category 3</primary></indexterm> category
3 commands return a single value using an environment variable specified
as the first parameter to the command (for these special commands, the first
parameter has the name <symbol role="Variable">variable</symbol>). If this
return value is immediately used in an expression, the special environment
variable &ldquo;-&ldquo; may be used in place of a variable name. When <command>dtksh</command> encounters &ldquo;-&ldquo; as the name of the environment
variable in which the return value is to be returned, it instead returns
the result as the value of the command. This allows the shell script to
embed the command call in another command call. This feature only works
for commands that return a single value, and the value is returned in the
first parameter. For example:</para>
<programlisting>XtDisplay DISPLAY $FORM
XSync $DISPLAY true</programlisting>
<para>can be replaced by the equivalent statement:</para>
<programlisting>XSync $(XtDisplay &ldquo;-&ldquo; $FORM) true</programlisting>
<para>The reference to <filename>$DISPLAY</filename> is replaced with the
value returned by the call to <command>XtDisplay</command>.</para>
<para>This capability is available for all category 3 commands except those
that create a widget, those that return more than a single value, and those
whose first parameter is not a named variable. Commands that do not accept
&ldquo;-&ldquo; as the environment variable name include the following:
</para>
<itemizedlist remap="Bullet1"><listitem><para><filename>XtInitialize()</filename></para>
</listitem><listitem><para><filename>XtCreateApplicationShell()</filename></para>
</listitem><listitem><para><filename>XtCreatePopupShell()</filename></para>
</listitem><listitem><para><filename>XtCreateManagedWidget()</filename></para>
</listitem><listitem><para><filename>XtCreateWidget()</filename></para>
</listitem><listitem><para>All commands of the form:</para>
<programlisting>XmCreate...()</programlisting>
</listitem><listitem><para>Most commands of the form:</para>
<programlisting>tt_...()</programlisting>
</listitem></itemizedlist>
</sect2>
</sect1>
<sect1 id="DKSUG.Intro.div.15">
<title>Initializing the Xt Intrinsics<indexterm><primary>Xt Intrinsics</primary>
<secondary>initialize</secondary></indexterm><indexterm><primary>initialize
Xt Intrinsics</primary></indexterm></title>
<para>A <command>dtksh</command> script must first initialize the Xt Intrinsics
before it can call any of the Xlib, Xt, Motif, or <command>libDt</command>
commands. You accomplish this by invoking the <command><indexterm><primary>XtInitialize</primary></indexterm>XtInitialize</command> command, which returns
an application shell widget. As is true for all <command>dtksh</command>
commands that return a widget ID, <command>XtInitialize</command> returns
the widget ID in the environment variable that is the first argument. For
example, in:</para>
<programlisting>XtInitialize TOPLEVEL myShellName Dtksh $0 &ldquo;$@&rdquo;
</programlisting>
<para>the widget ID is returned in the environment variable <command>TOPLEVEL</command>.</para>
<para><command>dtksh</command> provides a default <filename>app-defaults</filename>
file, which is used if the call to <command>XtInitialize</command> specifies
an application class name of <command>Dtksh</command>. This
<filename>app-defaults</filename> file contains the standard set of <command>Dt</command>
application default values, so <command>dtksh</command> applications have
a consistent look with other <command>Dt</command> applications.</para>
<sect2 id="DKSUG.Intro.div.16">
<title>Creating Widgets<indexterm><primary>widget</primary><secondary>create</secondary></indexterm><indexterm><primary>create widget</primary></indexterm></title>
<para>There are several commands you can use to create widgets:</para>
<informaltable>
<tgroup cols="2" colsep="0" rowsep="0">
<colspec align="left" colwidth="235*">
<colspec align="left" colwidth="221*">
<tbody>
<row>
<entry align="left" valign="top"><para><command>XtCreateWidget</command><indexterm>
<primary>XtCreateWidget</primary></indexterm></para></entry>
<entry align="left" valign="top"><para>Creates an unmanaged widget.</para></entry>
</row>
<row>
<entry align="left" valign="top"><para><command>XtCreateManagedWidget</command><indexterm>
<primary>XtCreateManagedWidget</primary></indexterm></para></entry>
<entry align="left" valign="top"><para>Creates a managed widget.</para></entry>
</row>
<row>
<entry align="left" valign="top"><para><command>XtCreateApplicationShell</command><indexterm>
<primary>XtCreateApplicationShell</primary></indexterm></para></entry>
<entry align="left" valign="top"><para>Creates an application shell.</para></entry>
</row>
<row>
<entry align="left" valign="top"><para><command>XtCreatePopupShell</command><indexterm>
<primary>XtCreatePopupShell</primary></indexterm></para></entry>
<entry align="left" valign="top"><para>Creates a pop-up shell.</para></entry>
</row>
<row>
<entry align="left" valign="top"><para><command>XmCreate</command>&lt; <emphasis>widgettypes</emphasis>></para></entry>
<entry align="left" valign="top"><para>Creates an unmanaged widget.</para></entry>
</row></tbody></tgroup></informaltable>
<para>There is a specific format for each of these commands that you must
follow. For example, suppose you want to create an unmanaged push button
widget as a child of the top-level widget. You can use either <command>XtCreateWidget</command> or <command>XmCreatePushButton</command>. The formats
for these commands are:</para>
<itemizedlist remap="Bullet1"><listitem><para><computeroutput>XtCreateWidget</computeroutput> <emphasis>variable name widgetclass $parent [resource:value
...]</emphasis><indexterm><primary>XtCreateWidget</primary></indexterm></para>
</listitem><listitem><para><computeroutput>XmCreatePushButton</computeroutput> <emphasis>variable $parent name [resource:value ...]</emphasis><indexterm><primary>XmCreatePushButton</primary></indexterm></para>
</listitem></itemizedlist>
<para>The actual commands to create a push button widget are:</para>
<programlisting>XtCreateWidget BUTTON button XmPushButton $TOPLEVEL
XmCreatePushButton BUTTON $TOPLEVEL button</programlisting>
<para>Each of the preceeding commands do exactly the same thing: create an
unmanaged push button. Note that no resource values are set. Suppose that
you want the background color of the push button to be red, and the foreground
color to be black. You can set the values of these resources this way:</para>
<programlisting>XtCreateWidget BUTTON button XmPushButton $TOPLEVEL \
background:Red \
foreground:Black
XmCreatePushButton BUTTON $TOPLEVEL button\
background:Red \
foreground:Black</programlisting>
<para>All of the C functions that create a widget return a<indexterm><primary>widget</primary><secondary>handle</secondary></indexterm><indexterm><primary>handle</primary></indexterm> widget ID, or ID. The corresponding <command>dtksh</command> commands set an environment variable equal to the widget
ID. These are category 3 commands, so the first argument is the name of
the environment variable in which to return the widget ID. The widget ID
is an ASCII string used by <command>dtksh</command> to access the actual
widget pointer. Either of the following commands could be used to create
a new form widget; however, in each case the widget ID for the new form widget
is returned in the environment variable <command>FORM</command>:</para>
<itemizedlist remap="Bullet1"><listitem><para><command>XtCreateManagedWidget
FORM name XmForm $PARENT</command><indexterm><primary>XtCreateManagedWidget</primary></indexterm></para>
</listitem><listitem><para><command>XmCreateForm FORM $PARENT name</command><indexterm>
<primary>XmCreateForm</primary></indexterm></para>
</listitem></itemizedlist>
<para>After either of these commands, you can use <filename>$FORM</filename>
to reference the new form widget. For example, you could use this command
to create a label widget within the new form widget:</para>
<programlisting>XmCreateLabel LABEL $FORM name\
labelString:&rdquo;Hi Mom&rdquo; \
CH_FORM \
leftAttachment:ATTACH_FORM<indexterm><primary>XmCreateLabel</primary></indexterm></programlisting>
<note>
<para>There is a special widget ID called NULL, provided for cases where
a shell script may need to specify a NULL widget. For example, to disable
the <command>defaultButton</command> resource for a form widget, use the
command <command>X</command><command>tSetValues $FORM defaultButton:NULL</command></para>
</note>
</sect2>
</sect1>
<sect1 id="DKSUG.Intro.div.17">
<title>Using a Callback<indexterm><primary>callback</primary></indexterm></title>
<para>A callback is a function or procedure that is executed when an event
or combination of events occurs. For example, a callback is used to achieve
the desired result when a push button is &ldquo;pressed.&rdquo; It is
easy for a <command>dtksh</command> shell script to assign a command to be
activated whenever a particular callback is invoked for a widget. The command
could be as simple as a string of commands blocked together, or the name
of the shell function to invoke.</para>
<sect2 id="DKSUG.Intro.div.18">
<title>Registering a Callback<indexterm><primary>callback</primary><secondary>register</secondary></indexterm><indexterm><primary>register callback</primary>
</indexterm></title>
<para>An application registers a callback with a widget to specify a condition
in which it is interested and to specify what action should occur when that
condition occurs. The callback is registered using <command><indexterm>
<primary>XtAddCallback</primary></indexterm>XtAddCallback</command>. The
action can be any valid <command>dtksh</command> command. For example:</para>
<programlisting>XtAddCallback $WIDGET activateCallback &ldquo;ActivateProc&rdquo;
XtAddCallback $WIDGET activateCallback \
&ldquo;XtSetSensitive $BUTTON false&rdquo;
</programlisting>
</sect2>
<sect2 id="DKSUG.Intro.div.19">
<title>Passing Data to a Callback<indexterm><primary>callback</primary><secondary>pass data to</secondary></indexterm></title>
<para>A callback needs to be passed context information, so it can determine
what condition led to its call. For a C procedure, this information is typically
passed in a <command>callData</command> structure. For example, a scale
widget invoking a <command>valueChangedCallback</command> passes an instance
of the following structure in <command>callData</command>:</para>
<programlisting>typedef struct {
int reason;
XEvent event;
int value;
}XmScaleCallbackStruct;</programlisting>
<para>The C application's callback then does something like:</para>
<programlisting>if (scaleCallData->reason == XmCR_VALUE_CHANGED)
{
eventType = scaleCallData->event->type;
display = scaleCallData->event->xany.display;
}</programlisting>
<para>Similarly, when a callback is invoked in <command>dtksh</command>, the
following special environment variable is set up before the callback command
executes:</para>
<programlisting>CB_WIDGET</programlisting>
<para>This is set to the widget ID for the widget that is invoking the callback.
</para>
<programlisting>CB_CALL_DATA</programlisting>
<para>This is set to the address of the <command>callData</command> structure
passed by the widget to the callback.</para>
<para>The <filename><indexterm><primary>CB_CALL_DATA</primary></indexterm>CB_CALL_DATA</filename> environment variable represents a pointer to a structure, and
access to its fields uses a syntax similar to that of C. Nested environment
variables are defined, named the same as the fields of the structure (but
all in uppercase), and a dot is used to indicate containment of an element
in a structure. Thus, the previous C code to access the <command>callData</command> provided by the scale widget translates to:</para>
<programlisting>if [ ${CB_CALL_DATA.REASON} = &ldquo;CR_VALUE_CHANGED&rdquo; ]; then
eventType=${CB_CALL_DATA.EVENT.TYPE}
display=${CB_CALL_DATA.EVENT.XANY.DISPLAY}
fi</programlisting>
<para>The same is true of the event structure within the <command>callData</command> structure.</para>
<para>For most callback structures, the shell script is able to reference
any of the fields defined for the particular callback structure, using the
technique described earlier. In most cases, the shell script is not able
to alter the values of the fields within these structures. The exception
to this is the <command>XmTextVerifyCallbackStruct</command>, which is available
during the <command>losingFocusCallback</command>, the <command>modifyVerifyCallback</command> and the <command>motionVerifyCallback</command> for the text widget.
<command>dtksh</command> supports the modification of certain fields within
this structure, to the extent that it is supported by Motif. The following
fields within the callback structure are capable of being modified:</para>
<itemizedlist remap="Bullet1"><listitem><para><filename>CB_CALL_DATA.DOIT</filename></para>
</listitem><listitem><para><filename>CB_CALL_DATA.STARTPOS</filename></para>
</listitem><listitem><para><filename>CB_CALL_DATA.TEXT.PTR</filename></para>
</listitem><listitem><para><filename>CB_CALL_DATA.TEXT.LENGTH</filename></para>
</listitem><listitem><para><filename>CB_CALL_DATA.TEXT.FORMAT</filename></para>
</listitem></itemizedlist>
<para>This is an example of how one of these fields can be modified:</para>
<itemizedlist remap="Bullet1"><listitem><para><filename>CB_CALL_DATA.DOIT=&rdquo;false&rdquo;</filename></para>
</listitem><listitem><para><filename>CB_CALL_DATA.TEXT.PTR=&rdquo;*&rdquo;</filename></para>
</listitem><listitem><para><filename>CB_CALL_DATA.TEXT.LENGTH=1</filename></para>
</listitem></itemizedlist>
</sect2>
</sect1>
</chapter>
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