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Author image Dmitry Karasik


Prima::VB::VBLoader - Visual Builder file loader


The module provides functionality for loading resource files, created by Visual Builder. After the successful load, the newly created window with all children is returned.


The simple way to use the loader is as that:

        use Prima qw(Application);
        use Prima::VB::VBLoader;
        Prima::VBLoad( './your_resource.fm',
                Form1 => { centered => 1 },
        )-> execute;

A more complicated but more proof code can be met in the toolkit:

        use Prima qw(Application);
        eval "use Prima::VB::VBLoader"; die "$@\n" if $@;
        $form = Prima::VBLoad( $fi,
                'Form1'     => { visible => 0, centered => 1},
        die "$@\n" unless $form;

All form widgets can be supplied with custom parameters, all together combined in a hash of hashes and passed as the second parameter to VBLoad() function. The example above supplies values for ::visible and ::centered to Form1 widget, which is default name of a form window created by Visual Builder. All other widgets are accessible by their names in a similar fashion; after the creation, the widget hierarchy can be accessed in the standard way:

        $form = Prima::VBLoad( $fi,
                'StartButton' => {
                        onMouseOver => sub { die "No start buttons here\n" },
        $form-> StartButton-> hide;

In case a form is to be included not from a fm file but from other data source, AUTOFORM_REALIZE call can be used to transform perl array into set of widgets:

        $form = AUTOFORM_REALIZE( [ Form1 => {
                class   => 'Prima::Window',
                parent  => 1,
                profile => {
                        name => 'Form1',
                        size => [ 330, 421],
                }], {});

Real-life examples are met across the toolkit; for instance, Prima/PS/setup.fm dialog is used by Prima::PS::Setup.



check_version HEADER

Scans HEADER, - the first line of a .fm file for version info. Returns two scalars - the first is a boolean flag, which is set to 1 if the file can be used and loaded, 0 otherwise. The second scalar is a version string.


Depending on value of boolean flag Prima::VB::VBLoader::builderActive performs the following: if it is 1, the SUB text is returned as is. If it is 0, evaluates it in sub{} context and returns the code reference. If evaluation fails, EXTRA_DATA is stored in Prima::VB::VBLoader::eventContext array and the exception is re-thrown. Prima::VB::VBLoader::builderActive is an internal flag that helps the Visual Builder use the module interface without actual SUB evaluation.


WIDGETS is an array reference that contains evaluated data of the read content of .fm file ( its data format is preserved). PARAMETERS is a hash reference with custom parameters passed to widgets during creation. The widgets are distinguished by the names. Visual Builder ensures that no widgets have equal names.

AUTOFORM_REALIZE creates the tree of widgets and returns the root window, which is usually named Form1. It automatically resolves parent-child relations, so the order of WIDGETS does not matter. Moreover, if a parent widget is passed as a parameter to a children widget, the parameter is deferred and passed after the creation using ::set call.

During the parsing and creation process internal notifications can be invoked. These notifications (events) are stored in .fm file and usually provide class-specific loading instructions. See Events for details.


Reads FILENAME in .fm file format, checks its version, loads, and creates widget tree. Upon successful load the root widget is returned. The parsing and creation is performed by calling AUTOFORM_REALIZE. If loading fails, die() is called.


A wrapper around AUTOFORM_CREATE, exported in Prima namespace. FILENAME can be specified either as a file system path name, or as a relative module name. In a way,

        Prima::VBLoad( 'Module::form.fm' )


                Prima::Utils::find_image( 'Module' 'form.fm'))

are identical. If the procedure finds that FILENAME is a relative module name, it calls Prima::Utils::find_image automatically. To tell explicitly that FILENAME is a file system path name, FILENAME must be prefixed with < symbol ( the syntax is influenced by CORE::open ).

%PARAMETERS is a hash with custom parameters passed to widgets during creation. The widgets are distinguished by the names. Visual Builder ensures that no widgets have equal names.

If the form file loaded successfully, returns the form object reference. Otherwise, undef is returned and the error string is stored in $@ variable.


The events, stored in .fm file are called during the loading process. The module provides no functionality for supplying the events during the load. This interface is useful only for developers of Visual Builder - ready classes.

The events section is located in actions section of widget entry. There can be more than one event of each type, registered to different widgets. NAME parameter is a string with name of the widget; INSTANCE is a hash, created during load for every widget provided to keep internal event-specific or class-specific data there. extras section of widget entry is present there as an only predefined key.


Called upon beginning of widget tree creation.


Called after the creation of a form, which reference is contained in ROOT_WIDGET.


Called after the creation of the widget. The newly created widget is passed in WIDGET


Called before child of WIDGET is created with CHILD_NAME as name.


Called after child of WIDGET is created; the newly created widget is passed in CHILD_WIDGET.


Called after the creation of all widgets is finished.


The idea of format of .fm file is that is should be evaluated by perl eval() call without special manipulations, and kept as plain text. The file begins with a header, which is a #-prefixed string, and contains a signature, version of file format, and version of the creator of the file:

        # VBForm version file=1 builder=0.1

The header can also contain additional headers, also prefixed with #. These can be used to tell the loader that another perl module is needed to be loaded before the parsing; this is useful, for example, if a constant is declared in the module.

        # [preload] Prima::ComboBox

The main part of a file is enclosed in sub{} statement. After evaluation, this sub returns array of paired scalars, where each first item is a widget name and second item is hash of its parameters and other associated data:

                return (
                        'Form1' => {
                                class   => 'Prima::Window',
                                module  => 'Prima::Classes',
                                parent => 1,
                                code   => GO_SUB('init()'),
                                profile => {
                                        width => 144,
                                        name => 'Form1',
                                        origin => [ 490, 412],
                                        size => [ 144, 100],

The hash has several predefined keys:

actions HASH

Contains hash of events. The events are evaluated via GO_SUB mechanism and executed during creation of the widget tree. See Events for details.


Contains a code, executed before the form is created. This key is present only on the root widget record.

class STRING

Contains name of a class to be instantiated.

extras HASH

Contains a class-specific parameters, used by events.

module STRING

Contains name of perl module that contains the class. The module will be use'd by the loader.

parent BOOLEAN

A boolean flag; set to 1 for the root widget only.

profile HASH

Contains profile hash, passed as parameters to the widget during its creation. If custom parameters were passed to AUTOFORM_CREATE, these are coupled with profile ( the custom parameters take precedence ) before passing to the create() call.


Dmitry Karasik, <dmitry@karasik.eu.org>.


Prima, VB