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Palm Database Programming — The Electronic Version
Chapter 4: Writing Palm Applications
This material was published in 1999. See the free
Palm OS Programming
online course I developed for
CodeWarriorU for some updated material.
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Contents
Applications
Before you can start building your own applications, it's important
that you understand what an application is and how it gets started by
the operating system.
What's an Application?
As mentioned in Chapter 2, an application is in fact a resource
database. The resources in the database contain the compiled code, the
initial values of global variables, and any user interface your
application requires. Your development tool creates these resources
for you. To launch the application, the system opens the database,
jumps to a fixed address, and runs the compiled code.
Type and Creator ID
To identify a resource database as an application, Palm OS uses the
database type "appl." Don't use this type for any database
you create; it's reserved exclusively for applications.
Every application requires a unique creator ID. The creator ID
identifies the application to the device. It also links all databases
used by an application together as part of the HotSync process. To
prevent conflicts, creator IDs are registered with Palm Computing.
Registration can be done in a matter of minutes through the Palm
Computing Web site at www.palm.com/devzone/crid/cridsub.html. Palm
Computing reserves creator IDs that consist entirely of lowercase
letters for its own use, so choose an ID th at contains at least one
uppercase letter or one nonalphabetic character. The creator ID is
often the initials or an abbreviation of the developer's or company's
name. In your planning for a new application, be sure to register a
creator ID early on.
On the CD-ROM you'll find the source and executable for the Creator
ID Viewer sample, which lists the creator IDs of all applications
installed on your Palm device.
Why Register a Creator ID?
No two applications can have the same creator ID, because the two
will conflict and overwrite each other when installed. That's why it's
important to register your creator IDs with Palm Computing, since it
guarantees uniqueness.
For testing purposes you can get away with reusing a creator ID or
else using an unregistered ID. Use the sample Creator ID Viewer
application to list all the creator IDs on the device and make sure
your test programs don't conflict with an application you've already
installed. But as soon as you start developing a "real"
application that you plan to give or sell to others, you should
register a creator ID for it.
All creator IDs used in this book have been registered.
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Copyright ©1999 by Eric Giguere. All rights reserved.
From Palm Database Programming: The Complete Developer's Guide.
Reprinted here with permission from the publisher. Please see the
copyright
and disclaimer notices for more details.
If you find the material useful, consider buying one of
my books,
linking to this site from your own site or in your weblog,
or sending me a note.
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