Thursday, August 11, 2016

Simplifying the use of the Progress Bar.

The basic implementation of the progressBar widget allows the setting of the "fraction" property of the GtkProgressBar but using this options requires more on the Tcl-side than it needs to.

Combination of the new options -range and -steps along with the new sub-commands step, incr and reset help to simplify matters.

For simple lists use the step subcommand along with the the -steps option to indicate the progress of a small, known number of steps where feedback on the completion of each step is required. Setting the -steps option to 10, for example, will set the widget "fraction" property to 0.1 (1/10, i.e. 10%). Following this each time the step sub-command is called, the widget bar will expand in length by 10% until it reaches 100%. The step sub-command accepts an additional argument which will set the text content of the bar.

    set modules [list \
        apple.tcl \
        blackberry.tcl \
        cherry.tcl \
        damson.tcl \
        elderberry.tcl \
        fig.tcl \
        gooseberry.tcl \
        hawthorn.tcl]
   
    proc do_progress { box modules } {
   
    set steps [llength $modules]

    set pb [gnocl::progressBar]
    $pb configure -steps $steps -showText 1
   
    $box add $pb
    $pb reset
   
    for {set i 0} {$i <= $steps} {incr i} {
        after 300
        $pb step [lindex $modules $i]
    }
   
    if ( [$box class] == statusBar ) {
        $box unpack $pb
    } else {
        $box remove $pb
    }
   
    }

In the above example, the reset subcommand was used to set the display fraction to 0.0 and text to and empty string.

More complicated operations, such as sifting through a large number of database records, may only need indication of relative progress. In other words, specific feedback on each increment in the batch process is not required. In this case the incr sub-command should be used. As with step above, an optional string can be specified, but if this field is left empty and the widget -showText option set to 1, the percentage completion of the bar will be displayed.

set range [ expr 1000 + round (rand() * 10000) ]
set steps 20
$pb3 configure -steps $steps -range $range -showText 1

for {set i 0 } {$i < $range} {incr i} {
    # do something or delay
    after 1
    $pb3 incr
   
}