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<H2><A NAME="sec:11.4"><SPAN class="sec-nr">11.4</SPAN> <SPAN class="sec-title">Library
``pce_toc'': displaying hierarchies</SPAN></A></H2>
<A NAME="sec:toc"></A>
<P>The table-of-content library defines a <A class="" href="summary.html#class:window">window</A>
displaying a <A class="" href="summary.html#class:tree">tree</A> in an
explorer-like style. This library is programmed by refining its
base-class
<B>toc_window</B>. We will introduce this library using an example
exploring the filesystem. A screendump of this application is in <A class="fig" href="toc.html#fig:libtoc">figure
21</A>.
<P><A NAME="fig:libtoc"></A>
<CENTER>
<IMG SRC="libtoc.gif">
</CENTER>
<TABLE ALIGN=center WIDTH="75%"><TR><TD>
<B>Figure 21 : </B>Exploring the filesystem</TABLE>
<PRE class="code">
:- pce_autoload(toc_window, library(pce_toc)).
:- pce_autoload(report_dialog, library(pce_report)).
:- pce_begin_class(explorer, frame, "Explore the filesystem").
initialise(E, Dir:directory) :->
"Explore from directory"::
send_super(E, initialise, 'Simple explorer'),
send(E, append, new(DH, directory_hierarchy(Dir))),
send(new(view), right, DH),
send(new(report_dialog), below, DH).
open_node(E, Node:file) :->
"Show file content of opened node"::
get(E, member, view, View),
send(View, load, Node).
:- pce_end_class.
:- pce_begin_class(directory_hierarchy, toc_window,
"Browser for a directory-hierarchy").
initialise(FB, Root:directory) :->
send(FB, send_super, initialise),
get(Root, name, Name),
send(FB, root, toc_folder(Name, Root)).
expand_node(FB, D:directory) :->
"Called if a node is to be expanded"::
new(SubDirsNames, chain),
new(FileNames, chain),
send(D, scan, FileNames, SubDirsNames),
get(SubDirsNames, map, ?(D, directory, @arg1), SubDirs),
send(SubDirs, for_all,
message(FB, son, D,
create(toc_folder, @arg1?name, @arg1))),
get(FileNames, map, ?(D, file, @arg1), SubFiles),
send(SubFiles, for_all,
message(FB, son, D,
create(toc_file, @arg1?base_name, @arg1))).
open_node(FB, Node:file) :->
"Called if a file is double-clicked"::
send(FB?frame, open_node, Node).
:- pce_end_class.</PRE>
<P>Programming is achieved by subclassing <B>toc_window</B> and in some
cases the support classes <B>toc_folder</B> and <B>toc_file</B>,
representing expandable and leaf-nodes.
<P>Each node is assigned an <EM>identifier</EM>, a unique reference to
the node. In the example below we used <A class="" href="summary.html#class:file">file</A>
and <A class="" href="summary.html#class:directory">directory</A>
objects for this purpose. The identifier is the second argument to the
creation of the node. When omitted, the node is turned into an
identifier of itself. This distinction is used to hide the existence of
graphical node objects for users of the basic functionality.
<P>Below we describe the important methods of this package. We start
with the virtual methods on class <B>toc_window</B> that should be
refined by most applications.
<DL>
<DT><STRONG>toc_window ->expand_node:</STRONG> <VAR>Id:any</VAR></DT>
<DD class="defbody">
The user clicked the <CODE>[+]</CODE> sign or double-clicked a <B>toc_folder</B>.
This method is normally refined to add sub-nodes for <VAR>Id</VAR> to
the current node using <A NAME="idx:tocwindowsendson:494"></A>`<B>toc_window<CODE>-></CODE>son</B>'.
If the implementation of <B>toc_window</B> is activated at the end the
window will scroll such that as much as possible of the subtree below <VAR>Id</VAR>
is visible.</DD>
<DT><STRONG>toc_window ->open_node:</STRONG> <VAR>Id:any</VAR></DT>
<DD class="defbody">
Called on double-click on a <B>toc_file</B> node. The implementation of
<B>toc_window</B> is empty.</DD>
<DT><STRONG>toc_window ->select_node:</STRONG> <VAR>Id:any</VAR></DT>
<DD class="defbody">
Called after single-click on <B>toc_folder</B> or <B>toc_file</B>. Note
that double-clicking activates both <B><CODE>-></CODE>select_node</B>
and <B><CODE>-></CODE>open_node</B> and therefore the action
following select_node should execute quickly.</DD>
<DT><STRONG>toc_window <-popup:</STRONG> <VAR>Id:any</VAR></DT>
<DD class="defbody">
Popup:popup This method is called on a right-down. If it returns a <A class="" href="summary.html#class:popup">popup</A>
object this is displayed.
</DD>
</DL>
<P>The methods below are used for general querying and manipulation of
the hierarchy.
<DL>
<DT><STRONG>toc_window <-selection:</STRONG> <VAR></VAR></DT>
<DD class="defbody">
ChainOfNodes Returns a <A class="" href="summary.html#class:chain">chain</A>
holding the <A class="" href="summary.html#class:node">node</A> objects
that are currently selected.</DD>
<DT><STRONG>toc_window <-node:</STRONG> <VAR>Id:any</VAR></DT>
<DD class="defbody">
Node:toc_node Map a node-identifier to a node. Fails silently if this
identifier is not in the tree.</DD>
<DT><STRONG>toc_window ->root:</STRONG> <VAR>Root:toc_folder</VAR></DT>
<DD class="defbody">
Assign the hierarchy a (new) root.</DD>
<DT><STRONG>toc_window ->son:</STRONG> <VAR>Parent:any, Son:toc_node</VAR></DT>
<DD class="defbody">
Make a new node below the node representing <VAR>Parent</VAR>. If the
node is a leaf, <VAR>Son</VAR> is a subclass of <B>toc_file</B>,
otherwise it is a subclass of <B>toc_folder</B>.</DD>
<DT><STRONG>toc_window ->expand_root:</STRONG> <VAR></VAR></DT>
<DD class="defbody">
Expands the root-node. This is normally called from <B><CODE>-></CODE>initialise</B>
to get a sensible initial hierarchy.
</DD>
</DL>
<P>The classes <B>toc_folder</B> and <B>toc_file</B> are summarised
below. Subclassing may be used to modify interaction and/or store
additional information with the node.
<DL>
<DT><STRONG>toc_folder ->initialise:</STRONG> <VAR></VAR></DT>
<DD class="defbody">
Create an expandable node. <VAR>Id</VAR> defaults to the node object
itself and the two images to the standard opened/closed folder images.
Folders assume they can be expanded, <VAR>CanExpand</VAR> may be set to <A NAME="idx:off:495"></A><B>@off</B>
to indicate `an empty folder'.</DD>
<DT><STRONG>toc_file ->indicate:</STRONG> <VAR></VAR></DT>
<DD class="defbody">
Create a `file'-node from its <VAR>Label</VAR>, <VAR>Id</VAR> (defaults
to the created node object) and <VAR>Image</VAR> (defaults to a
`document' icon).
</DD>
</DL>
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