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<H2><A NAME="sec:A.2"><SPAN class="sec-nr">A.2</SPAN> <SPAN class="sec-title">Miscellaneous 
topics</SPAN></A></H2>

<P>This section discusses various topics that were omitted from the 
Guided Tour to keep it simple.

<H3><A NAME="sec:A.2.1"><SPAN class="sec-nr">A.2.1</SPAN> <SPAN class="sec-title">Specifying 
callback to prolog</SPAN></A></H3>

<P>Using the background popup of the behaviour editor, the object <A NAME="idx:prolog:615"></A><B>@prolog</B> 
(see <A class="sec" href="pceprolog.html">section 6</A>) can be added to 
the model. Select <B>Add Send Port</B> to add a new predicate to the <A NAME="idx:prolog:616"></A><B>@prolog</B> 
interface. Then type the name of the predicate. Now link the event-port 
of a control to the predicate and link the arguments.

<P>If the predicate is not defined, select `Edit' on menu of <A NAME="idx:prolog:617"></A><B>@prolog</B> 
to start PceEmacs on the source file. Now drag the predicate to the 
PceEmacs window. This will insert the head of the predicate at the 
caret. See <A class="fig" href="sec-A.2.html#fig:diaprolog">figure 38</A>

<P><A NAME="fig:diaprolog"></A>
<CENTER>
<IMG SRC="diaprolog.gif">
</CENTER>
<TABLE ALIGN=center WIDTH="75%"><TR><TD>
<B>Figure 38 : </B>Specifying Call-back to Prolog</TABLE>

<H3><A NAME="sec:A.2.2"><SPAN class="sec-nr">A.2.2</SPAN> <SPAN class="sec-title">Advanced 
example of behaviour</SPAN></A></H3>

<P><A class="fig" href="sec-A.2.html#fig:viewer">Figure 39</A> is the 
screen dump of an application and its behaviour model of a tool that 
shows all files in a directory and clicking on a file shows the file's 
contents in the editor to the left. It demonstrates various aspects of 
advanced features for specifying behaviour.

<P>
<UL>
<LI><I>The text-field <B>directory</B></I><BR>
Represented in the model by (1). It is a normal <A class="" href="summary.html#class:text_item">text_item</A>, 
but the <A NAME="idx:textitembothtype:618"></A>`<B>text_item<CODE>&lt;-&gt;</CODE>type</B>' 
field is set to `directory'. This implies the
<B><CODE>&lt;-</CODE>selection</B> of the text-item will return a <A class="" href="summary.html#class:directory">directory</A> 
object.
<LI><I>Showing the files of the directory</I><BR>
If the text-item is modified, a list of files in the directory should be 
shown in the `file_list', a <A class="" href="summary.html#class:list_browser">list_browser</A>. 
The method
<A NAME="idx:listbrowsersendmembers:619"></A>`<B>list_browser<CODE>-&gt;</CODE>members</B>' 
may be used to fill the browser with a collection of items. This method 
expects a <A class="" href="summary.html#class:chain">chain</A> object. 
The get method <A NAME="idx:directorygetfiles:620"></A>`<B>directory<CODE>&lt;-</CODE>files</B>' 
provides a chain holding the names of all files in the directory.

<P>Thus, the event-port `message' of the directory field must invoke the 
send-port `members' of the file-list. The argument should be the result 
of applying <B><CODE>&lt;-</CODE>files</B> on the <B><CODE>&lt;-</CODE>selection</B> 
of the text-entry field. To specify this, the get-port `selection' is <EM>expanded</EM> 
using the popup menu of this port. This operation adds (2) to the 
diagram. The system infers this expansion is an instance of class <A class="" href="summary.html#class:directory">directory</A> 
and shows the most useful get-ports in its get-port menu. The `files' 
get-port is added to (2) and linked to the activation relation between
<A NAME="idx:textitemsendmessage:621"></A>`<B>text_item<CODE>-&gt;</CODE>message</B>' 
and <A NAME="idx:listbrowsersendmembers:622"></A>`<B>list_browser<CODE>-&gt;</CODE>members</B>'.

<P>To <B>test</B> this part, put the Dialog editor in `run' mode, type 
the name of a directory and <B>ENTER</B> to activate the event-port. If 
anything goes wrong, the <B>Simulate</B> option of the various popup 
menus in the diagram may be used to test small parts of the model. The <EM>Documentation</EM> 
option of these menus may be used to view the relevant documentation 
from the online manual tools.
<LI><I>Specifying the initial directory as a parameter</I><BR>
Initialisation of the dialog is expressed by adding one or more <EM>init-ports</EM> 
to the diagram using the background menu. In this particular case, we 
would like to be able to pass a directory to start as a parameter. 
Hence, a <EM>parameter-port</EM> is added with the name `dir'. First, 
the <B><CODE>-&gt;</CODE>selection</B> is set using the parameter and 
then the item is
<B><CODE>-&gt;</CODE>executed</B> to activate its <B><CODE>-&gt;</CODE>message</B>.

<P>Code generation will append the directory parameter to the identifier 
of the <A NAME="idx:dialog2:623"></A><A class="pred" href="sec-A.1.html#dialog/2">dialog/2</A> 
clause. In this case, this clause will start as:

<PRE class="code">
dialog(viewer(Dir),
       [ ...
       ]).
</PRE>

<P>An instance is opened using the following calls:

<PRE class="code">
        ...,
        make_dialog(D, viewer(StartDir)),
        send(D, open),
        ...
</PRE>

<P>
<LI><I>Showing a file</I><BR>
The first step is to link the event-port `select_message' of the 
file_list to the file_contents (3) <A class="" href="summary.html#class:editor">editor</A> 
object's send-port `load'. This method expects a file. Due to the type 
conversion rules of class <A class="" href="summary.html#class:file">file</A>, 
the name of a file suffices, but the names from file_list are relative 
to the directory object (2). First, the
<B><CODE>&lt;-</CODE>selection</B> of the file_list is expanded, 
resulting in (5), a
<A class="" href="summary.html#class:dict_item">dict_item</A> object. 
The <A NAME="idx:dictitemgetkey:624"></A>`<B>dict_item<CODE>&lt;-</CODE>key</B>' 
contains the name of the file.

<P>The method <A NAME="idx:directorygetfile:625"></A>`<B>directory<CODE>&lt;-</CODE>file</B>' 
can be used to create a <A class="" href="summary.html#class:file">file</A> 
object from a name, that specifies an absolute path. A get-port `file' 
is added to (2) and this get-port is linked to the activation relation. 
This get operation requires the filename argument from (5).
</UL>

<P><A NAME="fig:viewer"></A>
<CENTER>
<IMG SRC="viewer.gif">
</CENTER>
<TABLE ALIGN=center WIDTH="75%"><TR><TD>
<B>Figure 39 : </B>A file viewer</TABLE>

<H3><A NAME="sec:A.2.3"><SPAN class="sec-nr">A.2.3</SPAN> <SPAN class="sec-title">Specifying 
conditional actions</SPAN></A></H3>

<P><A class="fig" href="sec-A.2.html#fig:diacond">Figure 40</A> shows an 
example of a conditional activation relation. A conditional relation is 
created making a connection from the fat dot in the middle of an 
activation relation to a send-port. Success or failure of the send-port 
will be interpreted as a condition on the activation relation.

<P><A NAME="fig:diacond"></A>
<CENTER>
<IMG SRC="diacond.gif">
</CENTER>
<TABLE ALIGN=center WIDTH="75%"><TR><TD>
<B>Figure 40 : </B>Conditional activation</TABLE>

<H3><A NAME="sec:A.2.4"><SPAN class="sec-nr">A.2.4</SPAN> <SPAN class="sec-title">Load 
and save formats</SPAN></A></H3>

<P>The Dialog Editor provides two load/save formats. The <B>Load</B>,
<B>Save</B>, <B>Save As</B> and <B>Save All</B> save and load the status 
of the dialog editor as an <font size=-1>XPCE</font> object using <A NAME="idx:objectsendsaveinfile:626"></A>`<B>object<CODE>-&gt;</CODE>save_in_file</B>'. 
This format loads quickly, but is rather vulnerable to future changes in 
the Dialog Editor or any of the graphical classes.

<P>Alternatively, the Dialog Editor can restore itself from the 
identifier of a <A NAME="idx:dialog2:627"></A><A class="pred" href="sec-A.1.html#dialog/2">dialog/2</A> 
clause generated by itself or (slightly) modified. In this case, the 
layout of the behaviour model will be lost.

<P>We advice to use Save/Load during application development. If, during 
the maintenance phase of your product it is necessary to modify a 
dialog, either simply edit the <A NAME="idx:dialog2:628"></A><A class="pred" href="sec-A.1.html#dialog/2">dialog/2</A> 
clause, or load both the application and the dialog editor and use <B>Reload 
From Id</B> to restart the Dialog Editor.

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