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Initial commit of OpenSPARC T2 architecture model.
[OpenSPARC-T2-SAM] / sam-t2 / devtools / amd64 / html / python / lib / node719.html
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54
55<H2><A NAME="SECTION0018130000000000000000">
5616.1.3 A (Very) Quick Look at Tcl/Tk</A>
57</H2>
58<P>
59The class hierarchy looks complicated, but in actual practice,
60application programmers almost always refer to the classes at the very
61bottom of the hierarchy.
62
63<P>
64Notes:
65
66<UL>
67<LI>These classes are provided for the purposes of
68organizing certain functions under one namespace. They aren't meant to
69be instantiated independently.
70
71<P>
72</LI>
73<LI>The <tt class="class">Tk</tt> class is meant to be instantiated only once in
74an application. Application programmers need not instantiate one
75explicitly, the system creates one whenever any of the other classes
76are instantiated.
77
78<P>
79</LI>
80<LI>The <tt class="class">Widget</tt> class is not meant to be instantiated, it
81is meant only for subclassing to make ``real'' widgets (in C++, this
82is called an `abstract class').
83</LI>
84</UL>
85
86<P>
87To make use of this reference material, there will be times when you
88will need to know how to read short passages of Tk and how to identify
89the various parts of a Tk command.
90(See section&nbsp;<A href="tkinter-basic-mapping.html#tkinter-basic-mapping">16.1.4</A> for the
91<tt class="module"><a href="module-Tkinter.html">Tkinter</a></tt> equivalents of what's below.)
92
93<P>
94Tk scripts are Tcl programs. Like all Tcl programs, Tk scripts are
95just lists of tokens separated by spaces. A Tk widget is just its
96<em>class</em>, the <em>options</em> that help configure it, and the
97<em>actions</em> that make it do useful things.
98
99<P>
100To make a widget in Tk, the command is always of the form:
101
102<P>
103<div class="verbatim"><pre>
104 classCommand newPathname options
105</pre></div>
106
107<P>
108<DL>
109<DT><STRONG><var>classCommand</var></STRONG></DT>
110<DD>denotes which kind of widget to make (a button, a label, a menu...)
111
112<P>
113</DD>
114<DT><STRONG><var>newPathname</var></STRONG></DT>
115<DD>is the new name for this widget. All names in Tk must be unique. To
116help enforce this, widgets in Tk are named with <em>pathnames</em>, just
117like files in a file system. The top level widget, the <em>root</em>,
118is called <code>.</code> (period) and children are delimited by more
119periods. For example, <code>.myApp.controlPanel.okButton</code> might be
120the name of a widget.
121
122<P>
123</DD>
124<DT><STRONG><var>options</var> </STRONG></DT>
125<DD>configure the widget's appearance and in some cases, its
126behavior. The options come in the form of a list of flags and values.
127Flags are proceeded by a `-', like unix shell command flags, and
128values are put in quotes if they are more than one word.
129</DD>
130</DL>
131
132<P>
133For example:
134
135<P>
136<div class="verbatim"><pre>
137 button .fred -fg red -text "hi there"
138 ^ ^ \_____________________/
139 | | |
140 class new options
141 command widget (-opt val -opt val ...)
142</pre></div>
143
144<P>
145Once created, the pathname to the widget becomes a new command. This
146new <var>widget command</var> is the programmer's handle for getting the new
147widget to perform some <var>action</var>. In C, you'd express this as
148someAction(fred, someOptions), in C++, you would express this as
149fred.someAction(someOptions), and in Tk, you say:
150
151<P>
152<div class="verbatim"><pre>
153 .fred someAction someOptions
154</pre></div>
155
156<P>
157Note that the object name, <code>.fred</code>, starts with a dot.
158
159<P>
160As you'd expect, the legal values for <var>someAction</var> will depend on
161the widget's class: <code>.fred disable</code> works if fred is a
162button (fred gets greyed out), but does not work if fred is a label
163(disabling of labels is not supported in Tk).
164
165<P>
166The legal values of <var>someOptions</var> is action dependent. Some
167actions, like <code>disable</code>, require no arguments, others, like
168a text-entry box's <code>delete</code> command, would need arguments
169to specify what range of text to delete.
170
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207<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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Full OpenSPARC architecture tarball including simulator, hypervisor, and OBP.