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File compression within eVB or VB.NET
One of the main problems when it comes
to using a Pocket PC to transfer or store data can be the
size of the data. This can especially be the case if you
are transferring data using a slower connection such as
GSM. An ideal solution is to compress the data to reduce
the size and time taken to transfer. Sapphire
Solutions Ltd have developed an easy-to-use utility
that can compress or decompress GZip files (.gz) and Zip
files (.zip) right from your eVB or VB.NET application.
Overview
You can download the demo
project of the Sapphire GZip DLL which
includes a personal use version of the utility. This utility
allows a selection of local files to be compressed or decompressed
into the popular .zip or a single file
into the .gz format. It is then possible
to use any compatible compression application on a remote
computer to compress or decompress these files, ideal for
integrating into a back-end system.
Running the Project
After downloading and unzipping the
Sapphire GZip demo project, you need to add the appropriate
version of the SapphireGZip.DLL to the
\Windows directory on your Pocket PC. If
you are using VB.NET, you will need to include the SapphireGZip.DLL
into the application directory of your program instead.
You can find the correct DLL in the unzipped project directory
under the appropriate sub-directory. Once you have done
this you can run the desired project file on the client
device.
Included with the demo project are two
files, Mini.bmp and readme.txt
that can be used for demonstration purposes. Simply copy
those files to the \My Documents folder
on your Pocket PC.
GZip files
The demo project shows how to compress
or decompress both the .gz and .zip
files. The GZip demo (shown above) takes a single file and
compresses it giving it the .gz file extension. Moving a
file to the right will compress it and moving it to the
left will decompress it.
Compressing files to the zip format
To compress a series of files the demo
project requires the destination zip file and a search string
for all the files to zip. It is possible to include any
sub directories which is ideal for backing up a particular
folder on your device.
Decompressing a zip file
To decompress a zip file onto the client
device, an existing zip file can be specified. It is possible
to extract specific files from the zip file, or alternatively,
all files. You can also specify whether you wish to use
the original path names that are stored within the zip file.
The Code
To implement compression functionality
in your own eVB or VB.NET application you only need to create
a few simple calls to the DLL.
Example: Linking the DLL using VB.NET
<DllImport("SapphireGZip.dll")>
_
Public Function sZip( _
ByVal sFileIn As
String, _
ByVal sFileOut
As String, _
ByVal lSubDirs
As Integer, _
ByVal lLicence
As Integer) As
Integer
End Function
Example: Linking the DLL using eVB
Declare Function
sZip _
Lib "SapphireGZip.dll"
( _
ByVal sFileIn As
String, _
ByVal sFileOut
As String, _
ByVal lSubDirs
As Long, _
ByVal lLicence
As Long) As
Long
A simple example on how to create a
zip file:
lResult = sZip(sSourceFiles, sDestFile,
lSubDirs, SapphireGZipLicence)
- lResult contains the number
of any possible error that may have been encountered.
- sSourceFiles is the name
or pattern of file(s) to compress.
- sDestFile is the name of
the zip file to create.
- lSubDirs is a flag indicating
whether to include sub directories. 1 = Yes, 0 = No.
- SapphireGZipLicence is the
licence number for registered users of the utility. For
the demo project, this will be 1234567890.
Where to find the demo
The product information page for the
latest Sapphire GZip utility allows you to download the
personal use version that includes the sample eVB and VB.NET
projects with the demo version of the DLL for each target
platform. This can be found at www.sapphire-solutions.co.uk/product.asp?product=GZIP.
Licence of use
For those that wish to simply experiment
with the utility or use it for personal projects, you can
use the utility absolutely free of charge.
For those that wish to include the utility
into their own commercial applications, they can purchase
a royalty-free licence for the utility online at http://www.sapphire-solutions.co.uk.
This is a one off payment that allows you to distribute
it in any projects created under the registered company.
Please refer to the web site for the latest prices.
Other utilities you may find useful
Sapphire Solutions Ltd have a variety
of other utilities that you may find useful or vital to
your application. Some of these are:
- Sapphire
RAS - Dial up a remote connection and manage phone
book.
- Sapphire
FTP - Communicate with a FTP server (includes directory
navigation).
- Sapphire
Encrypt - Encrypt or decrypt strings or files ensuring
its confidentiality.
- Sapphire
IrDA - Use your application to print on an IrDA enabled
printer.
- Sapphire
Buttons - Take control of other buttons on your device.
Please check www.sapphire-solutions.co.uk
for a full listing of available products.