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| 129 | .\" ======================================================================== |
| 130 | .\" |
| 131 | .IX Title "ERROR 1" |
| 132 | .TH ERROR 1 "2000-12-30" "perl v5.8.0" "User Contributed Perl Documentation" |
| 133 | .SH "NAME" |
| 134 | Tk::Error \- Method invoked to process background errors |
| 135 | .SH "SYNOPSIS" |
| 136 | .IX Header "SYNOPSIS" |
| 137 | Customization: |
| 138 | .PP |
| 139 | .Vb 1 |
| 140 | \& require Tk::ErrorDialog; |
| 141 | .Ve |
| 142 | .PP |
| 143 | or |
| 144 | .PP |
| 145 | .Vb 4 |
| 146 | \& sub Tk::Error |
| 147 | \& { |
| 148 | \& my ($widget,$error,@locations) = @_; |
| 149 | \& ... |
| 150 | .Ve |
| 151 | .PP |
| 152 | .Vb 1 |
| 153 | \& } |
| 154 | .Ve |
| 155 | .SH "DESCRIPTION" |
| 156 | .IX Header "DESCRIPTION" |
| 157 | The \fBTk::Error\fR method is invoked by perl/Tk when a background |
| 158 | error occurs. Two possible implementations are provided in the |
| 159 | distribution and individual applications or users can (re)define a \fBTk::Error\fR |
| 160 | method (e.g. as a perl sub) if they wish to handle background |
| 161 | errors in some other manner. |
| 162 | .PP |
| 163 | A background error is one that occurs in a command that didn't |
| 164 | originate with the application. For example, if an error occurs |
| 165 | while executing a callback specified with a |
| 166 | bind or a after |
| 167 | command, then it is a background error. For a non-background error, |
| 168 | the error can simply be returned up through nested subroutines |
| 169 | until it reaches the top-level code in the application; |
| 170 | then the application can report the error in whatever way it |
| 171 | wishes. When a background error occurs, the unwinding ends in |
| 172 | the Tk library and there is no obvious way for Tk to report |
| 173 | the error. |
| 174 | .PP |
| 175 | When Tk detects a background error, it saves information about the |
| 176 | error and invokes the \fBTk::Error\fR method later when Tk is idle. |
| 177 | .PP |
| 178 | \&\fBTk::Error\fR is invoked by perl/Tk as if by the perl code: |
| 179 | .PP |
| 180 | \&\ \fI$mainwindow\fR\->\fBTk::Error\fR(\fI\*(L"error message\*(R"\fR, \fIlocation ...\fR); |
| 181 | .PP |
| 182 | \&\fI$mainwindow\fR is the \fBMainWindow\fR associated with widget which |
| 183 | detected the error, \fI\*(L"error message\*(R"\fR is a string describing the error |
| 184 | that has been detected, \fIlocation\fR is a list of one or more \*(L"locations\*(R" |
| 185 | which describe the call sequence at the point the error was detected. |
| 186 | .PP |
| 187 | The locations are a typically a mixture of perl location reports giving |
| 188 | script name and line number, and simple strings describing locations in |
| 189 | core Tk or perl/Tk C code. |
| 190 | .PP |
| 191 | Tk will ignore any result returned by the \fBTk::Error\fR method. |
| 192 | If another error occurs within the \fBTk::Error\fR method |
| 193 | (for example if it calls \fBdie\fR) then Tk reports this error |
| 194 | itself by writing a message to stderr (this is to avoid infinite loops |
| 195 | due to any bugs in \fBTk::Error\fR). |
| 196 | .PP |
| 197 | If several background errors accumulate before \fBTk::Error\fR |
| 198 | is invoked to process them, \fBTk::Error\fR will be invoked once |
| 199 | for each error, in the order they occurred. |
| 200 | However, if \fBTk::Error\fR calls \fBTk\->break\fR, then |
| 201 | any remaining errors are skipped without calling \fBTk::Error\fR. |
| 202 | .PP |
| 203 | The \fBTk\fR module includes a default \fBTk::Error\fR subroutine |
| 204 | that simply reports the error on stderr. |
| 205 | .PP |
| 206 | An alternate definition is provided via : |
| 207 | .PP |
| 208 | \&\ \f(CW\*(C`require Tk::ErrorDialog;\*(C'\fR |
| 209 | .PP |
| 210 | that posts a dialog box containing the error message and offers |
| 211 | the user a chance to see a stack trace showing where the |
| 212 | error occurred. |
| 213 | .SH "BUGS" |
| 214 | .IX Header "BUGS" |
| 215 | If \fBafter\fR or \fBfileevent\fR are not invoked as methods of a widget |
| 216 | then perl/Tk is unable to provide a \fI$mainwindow\fR argument. |
| 217 | To support such code from earlier versions of perl/Tk |
| 218 | perl/Tk therefore calls \fBTk::Error\fR with string 'Tk' instead: |
| 219 | \&\fBTk\->Tk::Error\e(...\e)\fR. |
| 220 | In this case the \fBTk::Error\fR in \fBTk::ErrorDialog\fR and similar |
| 221 | implementations cannot \*(L"popup\*(R" a window as they don't know which display |
| 222 | to use. A mechanism to supply \fIthe\fR \fBMainWindow\fR in applications |
| 223 | which only have one (a very common case) should be provided. |
| 224 | .SH "SEE ALSO" |
| 225 | .IX Header "SEE ALSO" |
| 226 | Tk::bind |
| 227 | Tk::after |
| 228 | Tk::fileevent |
| 229 | .SH "KEYWORDS" |
| 230 | .IX Header "KEYWORDS" |
| 231 | background error, reporting |