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<TITLE> Declaring and Using Variables<A NAME=65> </A></TITLE>
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<A NAME=Contents> </A><H2><A NAME=SECTION00085000000000000000> Declaring and Using Variables<A NAME=65> </A></A></H2>
<P>
The private variables of a widget class do not need to be
declared. In fact they can be initialized and used anywhere by any
method. Usually, however, general purpose private variables are
initialized by the <tt>InitWidgetRec</tt> method and subwidget
variables are initialized in the <tt>ConstructWidget</tt> method.
<P>We have seen in the <tt>tixArrowButton:InitWidgetRec</tt> example that
the private variable <tt>data(count)</tt> was initialized there. Also,
the private variable <tt>data(w:button)</tt> was initialized in <tt>tixArrowButton:ConstructWidget</tt> and subsequently used in <tt>tixArrowButton:SetBindings</tt>.
<P>In contrast, public variables must be declared inside the class
declaration. The following arguments are used to declare the public
variables and specify various options for them:
<P>
<blockquote> <UL><P><LI><P><tt>-flag</tt>: As shown in the class declaration in figure
6-2, the <tt>-flag</tt> argument declares all the public
variables of the TixArrowButton class, <tt>-direction</tt> and <tt>-state</tt>
<P><LI><P><tt>-configspec</tt>: We can use the <tt>-configspec</tt> argument to
specify the details of each public variable. For example, the
following declaration
<P>
<blockquote> <P><tt> -configspec {<BR>
{-direction direction Direction e}<BR>
{-state state State normal}<BR>
}</tt>
<P></blockquote>
<P>specifies that the <tt>-direction</tt> variable has the resource
name <tt>direction</tt> and resource class <tt>Direction</tt>; its default
value is <tt>e</tt>. The application programmer can assign value to
this variable by using the <tt>-direction</tt> option in the command
line or by specifying resources in the Tk option database with its
resource name or class. The declaration of <tt>-state</tt> installs
similar definitions for that variable.
<P><LI><P><tt>-alias</tt>: The <tt>-alias</tt> argument is used to specify
alternative names for public variables. In our example, the setting
<P>
<blockquote> <P><tt> -alias {<BR>
{-dir -direction}<BR>
}</tt>
<P></blockquote>
<P>specifies that <tt>-dir</tt> is the same variable as <tt>-direction</tt>. Therefore, when the application issue the command
<P>
<blockquote> <P><tt> .up config -dir w
</tt>
<P></blockquote>
<P>it is the same as issuing
<P>
<blockquote> <tt> .up config -direction w
</tt>
<P></blockquote>
<P>
The <tt>-alias</tt> option provides only an alternative name for
the application programmer. Inside the widget's implementation code,
the variable is still accessed as <tt>data(-direction)</tt>, <em>not</em>
<tt>data(-dir)</tt>.
<P></UL>
</blockquote>
<P>
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<UL>
<LI> <A NAME=tex2html1279 HREF=subsubsection3_8_5_1.html#SECTION00085100000000000000> Initialization of Public Variables<A NAME=651> </A></A>
<LI> <A NAME=tex2html1280 HREF=subsubsectionstar3_8_5_2.html#SECTION00085200000000000000> Type Checker<A NAME=6511> </A></A>
<LI> <A NAME=tex2html1281 HREF=subsubsection3_8_5_3.html#SECTION00085300000000000000> Public Variable Configuration Methods<A NAME=652> </A></A>
<LI> <A NAME=tex2html1282 HREF=subsubsectionstar3_8_5_4.html#SECTION00085400000000000000> Configuration Methods and Public Variable Initialization<A NAME=6521> </A></A>
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