Using a ProgressBar is a great way to
show the user something is still happening when you are doing lots of
processing. Without it, the user wonders, "Is the application
still running? Why isn't it responding?" Figure 23-18 shows what a fairly typical progress bar looks
like. This screenshot was generated with the following code:
use Tk;
use Tk::ProgressBar;
my $mw = MainWindow->new(-title => 'ProgressBar example');
$progress = $mw->ProgressBar(
-width => 30,
-from => 0,
-to => 100,
-blocks => 50,
-colors => [0, 'green', 50, 'yellow' , 80, 'red'],
-variable => \$percent_done
)->pack(-fill => 'x');
$mw->Button(-text => 'Go!', -command=> sub {
for ($i = 0; $i < 1000; $i++) {
$percent_done = $i/10;
print "$i\n";
$mw->update; # otherwise we don't see how far we are.
}
})->pack(-side => 'bottom');
MainLoop;
Figure 23-18. A ProgressBar
The callback that is part of the Go button is just a quick way of
showing how to do something and update the ProgressBar as part of the
process. You could be loading a file, doing some number crunching, or
anything else that seems to cause your program to pause.
23.10.1. ProgressBar Options
Here is a list of options available for ProgressBar:
-anchor => 'n' | 's' | 'e' | 'w'
Determines the starting point of
the bar. For horizontal bars (such as our example), use
'e' or 'w'. Vertical bars use
's' or 'n'.
-blocks => number
The number of
blocks used in constructing the bar. The larger the number, the more
blocks. The default is 10.
-colors => [pos0, color0, pos1, color1,... ]
An anonymous list containing
positions and colors. The position is where to start using that
particular color in the bar. That color will be used until it finds
another position/color or runs out of room in the bar.
-from => number
The lower limit on the progress
bar. Defaults to 0. Nothing is displayed if you try to use a value on
the bar below this number.
-gap => amount
Controls the amount of space left
between blocks. Default is 1. Use 0 to get a solid bar.
-length => amount
The long dimension of the progress
bar as a valid screen distance. This is ignored if you use
-fill with the pack command. If
this is a vertical progess bar, this value will be used for the
height.
-resolution => amount
A real value specifying the resolution for
the scale. If greater than zero, the scale's value will always
be rounded to an even multiple of this value, as will tick marks and
the endpoints of the scale. If the value is less than zero, no
rounding occurs. Defaults to 1 (i.e., the value will be integral).
-to => number
Sets the the upper limit of the
progress bar. Defaults to 100. If you ask the progress bar to display
a value higher than this limit, the bar will be completely filled.
-variable => \$var
A scalar variable that holds the
progress bar's current value. Use this instead of configuring
the -value option all the time.
-value => amount
The value currently displayed on
the progress bar.
-width => amount
The amount of screen distance
allocated to the thin portion of the progress bar. For a horizontal
bar, this is the height; for a vertical progress bar, this becomes
the width.
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