Chris Dent > PurpleWiki-0.94 > PurpleWiki::View::Driver

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NAME ^

PurpleWiki::View::Driver - View driver base class

SYNOPSIS ^

The PurpleWiki::View::Driver is primarily used as a base class, because by itself it doesn't do anything but traverse a PurpleWiki::Tree. This example defines a view driver that extracts image links from a PurpleWiki::Tree.

    package PurpleWiki::View::getImages;
    use strict;
    use warnings;
    use PurpleWiki::View::Driver;

    use vars qw(@ISA);
    @ISA = qw(PurpleWiki::View::Driver);

    sub new {
        my $prototype = shift;
        my $class = ref($prototype) || $prototype;
        my $self = $class->SUPER::new(@_);

        # Object State
        $self->{images} = [];

        bless($self, $class);
        return $self;
    }

    sub view {
        my ($self, $tree) = @_;
        $self->SUPER::view($tree);
        return @{$self->{images}};
    }

    sub imageMain {
        my ($self, $nodeRef) = @_;
        push @{$self->{images}}, $nodeRef->href;
    }

    1;

DESCRIPTION ^

PurpleWiki::View::Driver is the base class used by all of the view drivers. Its default behavior is to recurse down a PurpleWiki::Tree depth first from left most (oldest) child to right most (youngest) child. Child nodes are represented as a list within a PurpleWiki::Tree, so left most means the first child in the list and right most means the last child in the list.

Other than the methods mentioned in the METHODS section, this class also uses AUTOLOAD to export pre, main, and post handling methods for every node type. Three generic handlers are also exported via AUTOLOAD and they are called simply "Pre()", "Main()", and "Post()" and get called on every node.

For example, for every node of type "section" the following handlers are exported via AUTOLOAD:

    sectionPre()
    sectionMain()
    sectionPost()

The pre handler is called before the node, the main is called to process the node, and the post handler is called after the main handler has finished. Since we're in a tree, the main handler may not finish until much recursion has occurred.

The default action of both the generic and node specific pre and post handlers is to do a no-op. The default generic Main handler is also a no-op. The only methods exported via AUTOLOAD which are not no-ops are the node specific main handlers. Their default action is to call recurse(), which is documented in the METHODS section below.

The calling order of the handlers is as follows:

    generic Pre handler (defaults to no-op)
    node specific Pre handler (defaults to no-op)

    generic Main handler (defaults to no-op)
    node specific Main handler (defaults to recurse())

    node specific Post handler (defaults to no-op)
    generic Post handler (defaults to no-op)

The only data passed into a handler is a reference to a node object. So for example, the resulting method calls when processing a "ul" node would be as follows:

    $self->Pre($nodeRef);
    $self->ulPre($nodeRef);

    $self->Main($nodeRef);
    $self->ulMain($nodeRef);

    $self->ulPost($nodeRef);
    $self->Post($nodeRef);

This calling order is defined in processNode(), so if you overload that method you could possibly change the calling order. Also remember that overloading a node specific main handler will stop the recursion at that node unless you explicitly call recurse() in your overloaded method.

OBJECT STATE ^

depth

The driver's current depth while recursing through the PurpleWiki::Tree. The value of depth should be 0 before and after a call to the view() method. The value of depth is changed in processNode() and so is only sure to be correct as long as processNode() hasn't been overloaded in another class.

Since our object is a blessed hash reference you retrieve the value of depth like this: $self->{depth}

METHODS ^

The following methods are explicitly defined in Driver.pm and are available for overloading. In addition to these all of the methods generated via the AUTOLOAD function are also availble for overloading. The functions defined via AUTOLOAD are talked about in the DESCRIPTION section.

new()

Returns a new PurpleWiki::View::Driver(). The state variable depth is set to 0 at this point.

view($wikiTree)

This method is the common entry point for most view drivers. This method should be overloaded in derived classes and should return whatever is appropriate for the derived class it's in.

This method returns nothing by default and it's only action is to call processNode() on the root of the wikiTree.

Every derived class should call $self->SUPER::view() in their overloaded version.

recurse($nodeRef)

If $nodeRef is a StructuralNode then recurse() calls traverse() on the node's content field and then calls traverse() on the node's children field.

If $nodeRef is an InlineNode, then recurse() simply calls traverse() on the node's children field.

This method returns nothing by default. This method should only be overloaded if you want to make major changes to how a PurpleWiki::Tree is processed.

This method is the default action for the node specific main handlers defined via AUTOLOAD.

traverse($nodeListRef)

Iterates through a list of nodes and calls processNode() on each one. This method should only be overloaded if you want to make major changes to how a PurpleWiki::Tree is processed. It returns nothing by default.

processNode($nodeRef)

Calls all of the handlers for a node and updates the value of the object state variable "depth." The default behavior is as follows:

This method returns nothing by default and should only be overloaded if you want to make major changes to how a PurpleWiki::Tree is processed.

noop($nodeRef)

Does nothing and returns nothing. This is the default behavior of all but the node specific main handlers. Sometimes it is useful to overload for debugging purposes.

AUTHORS ^

Matthew O'Connor, <matthew@canonical.org>

SEE ALSO ^

PurpleWiki::Tree, PurpleWiki::StructuralNode, PurpleWiki::InlineNode.

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