5.24.2013 How to get the files/folders inside a ZIP file

Ever wanted to make your own Zip Viewer? In this article we look at a simple code for listing the files/folders inside a ZIP file, without any third party libraries.


Compression softwares such as WinZIP, WinRAR, 7-zip has been one of the needed softwares for our PCs. We can compress dozens of files into a single file, also shrink its size at the same time, with these compression utilities. But what if we could make our own zip viewer?

We have looked into "How to create a .Zip File with your own program", which was based on a third party library named ZipFile. Unfortunately the library could not open some zip files, though the add to zip functionality just works fine. So I had to find another alternative for "opening" a zip file. So I found paszlib. It is available with the Lazarus installation, so there is no need to install any third party libraries.

So lets get on with a Quick Tutorial:

Quick Tutorial

Create a Application Project (Project-> New Project-> Application-> OK).

Drop a TFileNameEdit (from Misc tab), a TButton, TListBox, TLabel (all from Standard tab). You should create a form layout like the screenshot below:

Now set the Name property of the TLabel to lblCount. Also set the Filter of TFileNameEdit to:
ZIP Files (*.zip)|*.zip

Switch to source code view (F12). Add Zipper in the uses clause:

uses
  ... , zipper;

Now double click the Tbutton and enter:

var
  szip: TUnZipper;
  i: integer;
begin
  szip := TUnZipper.Create;
  szip.FileName := FileNameEdit1.FileName;
  szip.Examine;

  ListBox1.Clear;
  for i := 0 to szip.Entries.Count-1 do begin
    ListBox1.Items.Add(szip.Entries.Entries[i].ArchiveFileName);
  end;

  lblCount.Caption:='Total Entries found: '+inttostr(szip.Entries.Count);

  szip.free;
end;

Explanation:

var
  szip: TUnZipper;
...
  szip:=TUnZipper.Create;
  szip.FileName := FileNameEdit1.FileName;

We Initialize TUnZipper (not the popular TZipper type), because it can read the files inside the zip file. We set the Filename that we want to read.

  szip.Examine;

It checks the file for any defects and it reads the files and makes them available to our code.

  for i := 0 to szip.Entries.Count-1 do begin
    ListBox1.Items.Add(szip.Entries.Entries[i].ArchiveFileName);
  end;

We iterate through all the file items/entries that are in the zip file and add them to our Listbox. We can also use many other information available to us instead of ArchiveFileName. See the TZipFileEntry class declaration below:

  TZipFileEntry = Class(TCollectionItem)
...
  Public
    constructor Create(ACollection: TCollection); override;
    function IsDirectory: Boolean;
    function IsLink: Boolean;
    Procedure Assign(Source : TPersistent); override;
    Property Stream : TStream Read FStream Write FStream;
  Published
    Property ArchiveFileName : String Read GetArchiveFileName Write FArchiveFileName;
    Property DiskFileName : String Read FDiskFileName Write FDiskFileName;
    Property Size : Integer Read FSize Write FSize;
    Property DateTime : TDateTime Read FDateTime Write FDateTime;
    property OS: Byte read FOS write FOS;
    property Attributes: LongInt read FAttributes write FAttributes;
    Property CompressionLevel: TCompressionlevel read FCompressionLevel write FCompressionLevel;
  end;

We can also use, for example, Entries[i].IsDirectory or Entries[i].Size information to view extra information in our software. Hope to post another article with more options (such as adding files, extracting files etc.).

Now run the Project (F9 or Run-> Run). Open a .ZIP file and click the button. You will see a list of files and folders in the zip file.

Zipper (a.k.a. paszlib) can also be used in Console projects. So you can create command line programs with paszlib library.

Download the Sample Code ZIP

You can download an example source code zip file from here: http://db.tt/BkhyiN9i
Or here: http://bit.ly/18cGsOG
Size: 548 KB
The package contains compiled executable EXE file.