Dynamically creating gui objects on demand in Perl

Posted June 11th, 2009 by kaikokan

I've been working on my project for learning perl Gui programming. What I want to do is create a Gui interface for Linux commands. Not because I think there's any need for such a thing but just because I think it provides a good base for learning Perl. It's not meant to be production software but maybe I can turn it in to a learning tool for linux commands or something.

Previously..

In my previous article I described how I created a Window with a text block and how to show the output of the "ls" command (I made it as simple as possible on purpose, I know there are easier ways to execute the ls command).

Dynamic checkbox creation

I also created a box which contained checkboxes for a few of the options of the ls command. As I want to add more commands to the tool it would take me a lot of time to create all the checkboxes and a lot of copy pasting code. I don't think that's a good idea, so I've been thinking of some way of dynamically creating vertical boxes containing the checkboxes for all options per command. That way I can just create a VBOX by passing a command and it's options to a subroutine.

Object orientation

This is possible because the Gtk library is object oriented, so I can create objects in my subroutine and pass them back. I think I'm going to do something like subclassing the Vbox class in the future, at this moment I don't have a clue how to accomplish such a thing. For now I'll just start with some kind of proof of concept code. In my previous article I got to version 7 of the program so here I'll start with version 8.

2 Dimensional array

In this version I add a 2 dimensional array which is going to contain arrays of command options, this is not needed for this version as here I'll only use 2 commands and I know upfront it are only 2 commands. I want the program to be flexible so it will be easy to add any number of commands with their respective options without changing the code. That's why I want to use a 2 dimensional array, I want to be able to add anonymous arrays for every option dynamically.

Option hash

I also add a hash which contains key=>value pairs for a list of command options, this is only for testing purposes and I think I will try to read this information from a file in a future version.

A new Box

I also created a third Box which is the result of calling a subroutine with the previously created hash as argument.

my $box3 = &selectBoxCreator(%optionHash);

This creates a VBox which I later add to the HBox I can create as many boxes as I like this way, for example if I would create another hash containing all the options for the rm command, I could just pass the hash to the selectBoxCreator and I get back a new VBox which I can in turn add to the HBox.

Sub for dynamic Box creation

To accomplish this I added a sub to the code which creates a VBOX

# our new subroutine for creating a VBOX containing multiple checkboxes dynamically created from a hash
sub selectBoxCreator { #the %optionHash contians all our options with their description my %options = @_; #the new VBOX object my $newVBOX = Gtk2::VBox->new(FALSE, 0); #run a sub as many times as there are key,value pairs #$key and $value are filled with the $key=>$value pairs #for each step while ( my ($key, $value) = each(%options) ) { # I tried to do this in one sub, but that didn't work # So I created a sub checkboxFactory # I think it's because the anonymous sub for the toggled signal # is created in another scope this way # Therefore we get multiple anonymous subs # If I create everything here the sub is just reassigned # (that's my guess anyway, I'm just starting to learn this stuff) #here we create a new checkbox my $btnNew = &checkboxFactory($value,$key); #and pack it into our new VBOX $newVBOX->pack_start($btnNew, FALSE, FALSE, 0) } return $newVBOX; }

Sub for dynamic checkbox creation

And another sub needed for creation of the checkboxes

I get the value and the key which are passed from the call with shift, create a new checkbox with value as argument
value is the secription of the option.
In the anonymous sub I connect to the button I dereference the reference to the 2 dimensional array to get an array again.
I no it looks ugly, I hope there is a more readable way to do this, I couldn't get it to work in any other way. It seems we can only create a multi dimensional array using references and we can only push into arrays not into references. If anybody can show me a better way, please do so.

sub checkboxFactory
{
my $value = shift @_; # gets the firtst argument
my $key = shift @_; # gets the second argument
my $index; # create a index variable which is only ever seen by this checkbox, every checkbox has it's own
my $btn = Gtk2::CheckButton->new($value); # create a new Gtk checkbutton
$btn->show; # set it visible
#connect a sub to the toggled signal of this box
#this sub is anonymous so we can recreate it everytime
$btn->signal_connect('toggled' =>sub
{
if($btn->get_active)
{
#push returns new array lenght
#from inside to out $arrayMatrix is a reference that contains array references
#@{$arrayMatrix} dereferences $arrayMatrix to an array of references
#@{@{$arrayMatrix}[0]} dereferences the array reference on position 0 of
#@{$arrayMatrix} to an array of values
# to which we push our $key, returning a new array size
#test if $index has been filled before if not use push
#to push the $key to the end of the array
if (!defined $index){
$index=push (@{@{$arrayMatrix}[0]},$key);}
#in the other case there is an index for this option
#then this sub has run before
else {$arrayMatrix->[0][$index-1]=$key};
print @{$arrayMatrix->[0]};
}
else
#this part is run when the checkbox is unchecked
{
#remove the option from the array
$arrayMatrix->[0][$index-1]="";
print @{$arrayMatrix->[0]};
&textViewUpdate;
}
}
);
return $btn;

That's it for today I uploaded the code here:

http://www.handlewithlinux.com/downloads/code/commandViewerStep8.tar.gz

or read it online here:

http://www.handlewithlinux.com/downloads/code/commandViewerStep8

Read it in eclipse that's easier than online. I added a lot of comments to the code so it's a bit understandable.
It surprised me once again how easy to understand Perl can be, it really is a great language. I did encounter some difficulties understanding this reference and dereference stuff. But that's more accountable to my wishes than to the complexity of the language I guess.

If anybody knows a better way to accomplish what I did here. Please leave a comment.

Coming up:

In my next article I'll remove the static block of checkboxes and replace it with a dynamically changed box according to a selectbox. I'm thinking of adding a box to give a text to the command (like ls-l /usr/bin)
I'll see how far I get. I'm planning to rewrite this code to object oriented code, but I need to learn some more before that.