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Overview
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This article provides a fully featured unzip application written in VB, using the
capabilities of the Info-ZIP Unzip DLL. The zip application
demonstrates the abilities of the unzip DLL to handle all aspects of unzip operations -
password protection, directory listing, including directories whilst unzipping,
prompts for overwriting files - in face everything you've come to expect when using
tools like WinZIP (which isn't surprising, because WinZIP uses the same base
code!) The code also demonstrates some nice features such as
capturing
the Shell Browse for Folder Dialog to provide a powerful and user-friendly method for
picking folders and using the Registry to store
Most-Recently Used File Lists.
More usefully, perhaps, the unzipping code is wrapped up into a reusable class which
you can incorporate into your own projects. So, without further ado...
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Reusing the VB code - Quick Start
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To get the simplest overview of the code, extract these two files from the Unzip Sample
project:
Add these two files to a new project in VB, and then declare a
WithEvents instance of the cUnzip class:
Private WithEvents m_cUnzip As cUnzip
The simplest operation is to open and unzip a zip without password encryption.
This is all you need to do:
' Set the zip file:
m_cUnzip.ZipFile = sFIle
' Set the base folder to unzip to:
m_cUnzip.UnzipFolder = sFolder
' Unzip the file!
m_cUnzip.Unzip
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In More Detail
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Directory Listings
To get a directory of files within the zip, use the Directory
method. When this returns, you can use the FileCount property to get the number
of files in the zip, and the FileCompressionMethod, FileCompressionRatio,
FileCRC, FileDate, FileDirectory, FileEncrypted, FilePackedSize,
and FileSize methods to display information about the files.
You can restrict which files are extracted in an Unzip operation using the
FileSelected property. By default, this property is set to True for all files, just
set it to False for the files you don't want to extract.
Progress and Cancel
As Directory listings and Unzip operations are performed, the DLL will raise the
Progress event, which you can use to display status messages about the
directory operation, and Cancel events, which allows you to stop the directory or unzip
operation.
Dealing With Password Protected Zips
The PasswordRequest event is raised when you attempt to extract a file from an
encrypted ZIP. Here you can supply the password and optionally cancel the extract operation.
Overwrite Prompts
If you set the PromptToOverwrite option, you will also get OverwritePrompt
events to respond to whenever the ZIP DLL encounters an existing file. Through this method
you can decide whether to overwrite a given file or not and also whether the same response
should be applied to all other files in the ZIP.
The remainder of the properties of the class allow you to set unzipping options, such as
UseFolderNames, ExtractOnlyNewer and OverwriteExisting.
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