Page 1
Page 2
Page 3
Necessity is the mother of invention
It all started when I had a shareware program
rejected by a download site because the reviewer's PocketPC couldn't
start an embedded Visual Basic (eVB) component. Of course this
was completely irreproducible at first, which ticked me off, and
after a lot of messing around, I happened to stumble on the cause.
When an eVB program is uninstalled, ActiveSync removes everything
installed with it, usually including the eVB runtime system! From
the standpoint of all other eVB programs on the PPC, that's all
she wrote, or rather erased: they can't run.
What probably happened to the reviewer was
that he had been reviewing an eVB program, and then uninstalled
it before trying my program. My program couldn't start because
no eVB program would work at that point on that machine.
Installing eVB applications
The genesis of this is that when an eVB developer
wants to set up an installation package for a program, normally
(s)he would use the Application Install Wizard. The wizard is
part of the eVB development system, and is all very simple, but
one of the defaults, sitting in a very innocent looking little
check box, is "Include Device Runtime". The purpose
of this option is to include the EXE and DLL files that allow
eVB to run as part of the installation package. Now, this is a
little weird since these files are already in ROM and the copies
waste memory, so it's not at all obvious why this is done. We
can cut Microsoft a little slack by telling ourselves that this
practice ensures that the latest versions of the code are loaded,
and if you say it fast, it does make some sense.
When an eager user then installs such an eVB
program, two things happen: the eVB application and all the runtime
EXEs and DLLs are loaded, and equally importantly, the runtime
DLLs are registered in the PocketPC's registry. The registry holds
the key to all this. Among a lot of other stuff, the registry
has an entry that tells WinCE what to do when it encounters an
eVB program, that is, a file with a .vb extension. It is told
by the registry entry that the polite thing to do is to run PVBLOAD.EXE
and give it the .vb file to deal with. This is how eVB programs
get run.
The wheels fall off
All is just hunky dory up to this point, but
now comes the nasty part. When our trusting user uninstalls the
eVB program, ActiveSync tries to reverse everything that happened
when it was installed. All the application files are removed,
any runtime files loaded with it are removed, and all changes
to the registry are undone. If you say this very fast, and also
mumble a bit, it sounds kind of OK.
It's not. The machine is now in deep doo doo.
Next Page