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Portability. It's something VB
programmers haven't worried about, or probably even thought
about since the times of the 486, Windows 3.x and VB 4.
Sure, when VB 5 was released there were still some hold
out customers that wanted 16 bit applications, but for the
most part the notion of VB code needing to address portability
went the way of the dinosaur when Windows 95 and 98 had
fully taken over the PC market.
That was until CE came along. Of course
eMbedded Visual Basic is still interpreted code, so as VB
developers we still don't have to worry about compiling
for specific processors like C++ developers do, but there
are still multiple platforms. We often have to address the
fact that a client may want to run an application on both
a PocketPC and an HPC Pro.
The first, most obvious hurdle that
you must overcome is the simple real-estate issue. A Pocket
PC's screen is 260x320, whereas the HPC Pro might be either
480x24 0 or 480x480.
Then there are the more subtle differences:
the PocketPC uses a MenuBar control instead of a menu, the
PocketPC has a Form OK button, ADOCE connections and recordsets
have to be created from different libraries (i.e. ADOCE.Connection.3.0
on the PocketPC versus just ADOCE.Connection on the HPC
Pro), The SIP, form closing events. The list goes on.
If there's anything I hate doing as
a developer, it's repeating myself. Duplicating code across
projects not only is tedious, it's dangerous. It makes maintenance
a nightmare. Bug fixes, as well as upgrades and feature
changes have to be made in multiple places, and the more
lines of code you have, the greater the probability of making
a mistake or error.
The first key to making solutions portable
in the CE world is abstraction - moving the code out of
the form and into BAS files that you can call from anywhere.
This includes all event handling from the forms.
Let's begin by developing the ubiquitous
"Hello World" application to run on the PocketPC
and the HPC Pro. We'll have a textbox to enter our name
and a button that, when clicked, displays out "Hello"
message.
First create two project files, one
for each platform, and, if eVB didn't do it for you, add
one Form to each project. Next add a CommandButton
and TextBox to each Form. The properties for each
are not terribly important, except for one - keep the names
of analogous controls across projects identical. To make
things easier, name both forms frmMain, both CommandButtons
cmdHi and both TextBoxes txtName and save
the projects in separate folders. You can see what I ended
up with in Figures 1 and 2.
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