Specifications

2-1

HAPTER

OMMUNICATING WITH THE

YSTEM

CREEN

Introduction

An important aspect of the Series 3 is the way all the built-in applications communicate with the System

Screen application (also known as the Shell application):

• The name of any file currently open is displayed in bold in the file list in the System Screen

• This name is also displayed in any status window shown

• On a request from the System Screen, an application can close itself down tidily, saving any

changes to file as appropriate

• Alternatively, applications can be requested to switch files, to change which file they are

currently editing.

Applications use two mechanisms to communicate to the Series 3 OS their preferences concerning file

switching, as well as the name of the file they are currently editing:

• some data is written at compile time into a shell data file (.shd file) that is linked into the

application's .app file; this data includes the expected extension of any files to be edited, and the

default directory for these files, as well as the more basic point of whether the application is file-

based at all

• other data can be written at run time to various reserved Epoc statics; these include the full path

name of the file currently being edited.

Creating .shd files

The format of .ms files

The shell data of an application (see above) is expressed in source form in a file that typically has

extension .ms. For example, the contents of a file tele.ms could be:

Tele.TEL

\TEL\

Running the tool makeshd as follows

makeshd tele

would produce the file tele.shd from tele.ms (barring syntax errors in the .ms file).

The .shd file can then be combined into the final .app form of an application as discussed in the previous

chapter.

The first line in a .ms file has general form

<Name>[<.EXT>]

with the extension

.EXT

only being present for file-based applications. In that case,

.EXT

defines the

default extension for the application. In all cases,

Name

is the so-called public name of the application.

This must be a valid file name, that is, it must start with a letter and not exceed eight characters.