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129 | .\" ======================================================================== | |
130 | .\" | |
131 | .IX Title "Tk::Trace 3" | |
132 | .TH Tk::Trace 3 "2000-12-30" "Tk800.023" "perl/Tk Documentation" | |
133 | .SH "NAME" | |
134 | Tk::Trace \- emulate Tcl/Tk \fBtrace\fR functions. | |
135 | .SH "SYNOPSIS" | |
136 | .IX Header "SYNOPSIS" | |
137 | .Vb 1 | |
138 | \& use Tk::Trace | |
139 | .Ve | |
140 | .PP | |
141 | .Vb 4 | |
142 | \& $mw->traceVariable(\e$v, 'wru' => [\e&update_meter, $scale]); | |
143 | \& %vinfo = $mw->traceVinfo(\e$v); | |
144 | \& print "Trace info :\en ", join("\en ", @{$vinfo{-legible}}), "\en"; | |
145 | \& $mw->traceVdelete(\e$v); | |
146 | .Ve | |
147 | .SH "DESCRIPTION" | |
148 | .IX Header "DESCRIPTION" | |
149 | This class module emulates the Tcl/Tk \fBtrace\fR family of commands by | |
150 | binding subroutines of your devising to Perl variables using simple | |
151 | \&\fBTie::Watch\fR features. | |
152 | .PP | |
153 | Callback format is patterned after the Perl/Tk scheme: supply either a | |
154 | code reference, or, supply an array reference and pass the callback | |
155 | code reference in the first element of the array, followed by callback | |
156 | arguments. | |
157 | .PP | |
158 | User callbacks are passed these arguments: | |
159 | .PP | |
160 | .Vb 4 | |
161 | \& $_[0] = undef for a scalar, index/key for array/hash | |
162 | \& $_[1] = variable's current (read), new (write), final (undef) value | |
163 | \& $_[2] = operation (r, w, or u) | |
164 | \& $_[3 .. $#_] = optional user callback arguments | |
165 | .Ve | |
166 | .PP | |
167 | As a Trace user, you have an important responsibility when writing your | |
168 | callback, since you control the final value assigned to the variable. | |
169 | A typical callback might look like: | |
170 | .PP | |
171 | .Vb 6 | |
172 | \& sub callback { | |
173 | \& my($index, $value, $op, @args) = @_; | |
174 | \& return if $op eq 'u'; | |
175 | \& # .... code which uses $value ... | |
176 | \& return $value; # variable's final value | |
177 | \& } | |
178 | .Ve | |
179 | .PP | |
180 | Note that the callback's return value becomes the variable's final value, | |
181 | for either read or write traces. | |
182 | .PP | |
183 | For write operations, the variable is updated with its new value before | |
184 | the callback is invoked. | |
185 | .PP | |
186 | Only one callback can be attached to a variable, but read, write and undef | |
187 | operations can be traced simultaneously. | |
188 | .SH "METHODS" | |
189 | .IX Header "METHODS" | |
190 | .IP "$mw\->traceVariable(varRef, op => callback);" 4 | |
191 | .IX Item "$mw->traceVariable(varRef, op => callback);" | |
192 | \&\fBvarRef\fR is a reference to the scalar, array or hash variable you | |
193 | wish to trace. \fBop\fR is the trace operation, and can be any combination | |
194 | of \fBr\fR for read, \fBw\fR for write, and \fBu\fR for undef. \fBcallback\fR is a | |
195 | standard Perl/Tk callback, and is invoked, depending upon the value of | |
196 | \&\fBop\fR, whenever the variable is read, written, or destroyed. | |
197 | .ie n .IP "%vinfo = $mw\->traceVinfo(varRef);" 4 | |
198 | .el .IP "%vinfo = \f(CW$mw\fR\->traceVinfo(varRef);" 4 | |
199 | .IX Item "%vinfo = $mw->traceVinfo(varRef);" | |
200 | Returns a hash detailing the internals of the Trace object, with these | |
201 | keys: | |
202 | .Sp | |
203 | .Vb 10 | |
204 | \& %vinfo = ( | |
205 | \& -variable => varRef | |
206 | \& -debug => '0' | |
207 | \& -shadow => '1' | |
208 | \& -value => 'HELLO SCALAR' | |
209 | \& -destroy => callback | |
210 | \& -fetch => callback | |
211 | \& -store => callback | |
212 | \& -legible => above data formatted as a list of string, for printing | |
213 | \& ); | |
214 | .Ve | |
215 | .Sp | |
216 | For array and hash Trace objects, the \fB\-value\fR key is replaced with a | |
217 | \&\fB\-ptr\fR key which is a reference to the parallel array or hash. | |
218 | Additionally, for an array or hash, there are key/value pairs for | |
219 | all the variable specific callbacks. | |
220 | .IP "$mw\->traceVdelete(\e$v);" 4 | |
221 | .IX Item "$mw->traceVdelete($v);" | |
222 | Stop tracing the variable. | |
223 | .SH "EXAMPLE" | |
224 | .IX Header "EXAMPLE" | |
225 | .Vb 1 | |
226 | \& use Tk; | |
227 | .Ve | |
228 | .PP | |
229 | .Vb 1 | |
230 | \& # Trace a Scale's variable and move a meter in unison. | |
231 | .Ve | |
232 | .PP | |
233 | .Vb 6 | |
234 | \& $pi = 3.1415926; | |
235 | \& $mw = MainWindow->new; | |
236 | \& $c = $mw->Canvas(qw/-width 200 -height 110 -bd 2 -relief sunken/)->grid; | |
237 | \& $c->createLine(qw/100 100 10 100 -tag meter/); | |
238 | \& $s = $mw->Scale(qw/-orient h -from 0 -to 100 -variable/ => \e$v)->grid; | |
239 | \& $mw->Label(-text => 'Slide Me for 5 Seconds')->grid; | |
240 | .Ve | |
241 | .PP | |
242 | .Vb 1 | |
243 | \& $mw->traceVariable(\e$v, 'w' => [\e&update_meter, $s]); | |
244 | .Ve | |
245 | .PP | |
246 | .Vb 6 | |
247 | \& $mw->after(5000 => sub { | |
248 | \& print "Untrace time ...\en"; | |
249 | \& %vinfo = $s->traceVinfo(\e$v); | |
250 | \& print "Watch info :\en ", join("\en ", @{$vinfo{-legible}}), "\en"; | |
251 | \& $c->traceVdelete(\e$v); | |
252 | \& }); | |
253 | .Ve | |
254 | .PP | |
255 | .Vb 1 | |
256 | \& MainLoop; | |
257 | .Ve | |
258 | .PP | |
259 | .Vb 11 | |
260 | \& sub update_meter { | |
261 | \& my($index, $value, $op, @args) = @_; | |
262 | \& return if $op eq 'u'; | |
263 | \& $min = $s->cget(-from); | |
264 | \& $max = $s->cget(-to); | |
265 | \& $pos = $value / abs($max - $min); | |
266 | \& $x = 100.0 - 90.0 * (cos( $pos * $pi )); | |
267 | \& $y = 100.0 - 90.0 * (sin( $pos * $pi )); | |
268 | \& $c->coords(qw/meter 100 100/, $x, $y); | |
269 | \& return $value; | |
270 | \& } | |
271 | .Ve | |
272 | .SH "HISTORY" | |
273 | .IX Header "HISTORY" | |
274 | .Vb 2 | |
275 | \& Stephen.O.Lidie@Lehigh.EDU, Lehigh University Computing Center, 2000/08/01 | |
276 | \& . Version 1.0, for Tk800.022. | |
277 | .Ve | |
278 | .SH "COPYRIGHT" | |
279 | .IX Header "COPYRIGHT" | |
280 | Copyright (C) 2000 \- 2000 Stephen O. Lidie. All rights reserved. | |
281 | .PP | |
282 | This program is free software; you can redistribute it and/or modify it under | |
283 | the same terms as Perl itself. |