Why do I get an "abstract error" when calling TJclCompressArchive.Compress?

Question

I have the following code that always fails with an "Abstract Error":

  arch := TJclCompressArchive.Create(GetDesktop + 'Support.7z');
  try
    with arch do
    begin

      if FindFirst('*.log', faAnyFile, sr) = 0 then
      begin
        repeat
          AddFile(ExtractFileName(sr.Name),sr.Name);
        until FindNext(sr) <> 0;

        FindClose(sr);
      end;

      Compress; //this line throws the error
    end;
  finally
    arch.free;
  end;

However, I always get that error when trying to Compress. Any ideas on what I'm doing wrong here?

Answer 1

I believe you have to tell it which kind of JclCompressArchive to create, such as give it arch := TJcl7zCompressArchive.Create... instead of JclCompressArchive.Create().

If you look at the "Class Hierarchy" section of JclCompression.pas:

TJclCompressionArchive
   |
   |-- TJclCompressArchive
   |    |
   |    |-- TJclSevenzipCompressArchive
   |         |
   |         |-- TJclZipCompressArchive     handled by sevenzip ...
   |         |-- TJclBZ2CompressArchive     handled by sevenzip ...
   |         |-- TJcl7zCompressArchive      handled by sevenzip ...
   |         |-- TJclTarCompressArchive     handled by sevenzip ...
   |         |-- TJclGZipCompressArchive    handled by sevenzip ...
   |         |-- TJclXzCompressArchive      handled by sevenzip ...

Update
I think the proper way to use StackOverflow would have been to add a new question, since after the update, it's a completely different question.

I don't know why you're casting to TJclCompressArchive to AddFile() and Compress(), it seems to work for me without the casts

const
  FILENAME = 'Support.7z';
var
  archiveclass: TJCLUpdateArchiveClass;
  arch: TJclUpdateArchive;
  sr: TSearchRec;
begin
  archiveclass := GetArchiveFormats.FindUpdateFormat(FILENAME);

  if not Assigned(archiveclass) then
    raise Exception.Create('Could not determine the Format of ' + FILENAME);

  arch := archiveclass.Create(FILENAME);
  try
    // if FileExists(FILENAME) then // if you want to add any new files,
    //   arch.ListFiles;            // in addition to what is already there

    if FindFirst('*.pas', faAnyFile, sr) = 0 then
    begin
      repeat
        arch.AddFile(ExtractFileName(sr.Name),sr.Name);
      until FindNext(sr) <> 0;

      FindClose(sr);
    end;

    arch.Compress;
  finally
    arch.free;
  end;
end;