Create Zip archive from multiple in memory files in C#

Use ZipEntry and PutNextEntry() for this. The following shows how to do it for a file, but for an in-memory object just use a MemoryStream

FileStream fZip = File.Create(compressedOutputFile);
ZipOutputStream zipOStream = new ZipOutputStream(fZip);
foreach (FileInfo fi in allfiles)
{
    ZipEntry entry = new ZipEntry((fi.Name));
    zipOStream.PutNextEntry(entry);
    FileStream fs = File.OpenRead(fi.FullName);
    try
    {
        byte[] transferBuffer[1024];
        do
        {
            bytesRead = fs.Read(transferBuffer, 0, transferBuffer.Length);
            zipOStream.Write(transferBuffer, 0, bytesRead);
        }
        while (bytesRead > 0);
    }
    finally
    {
        fs.Close();
    }
}
zipOStream.Finish();
zipOStream.Close();

Using SharpZipLib for this seems pretty complicated. This is so much easier in DotNetZip. In v1.9, the code looks like this:

using (ZipFile zip = new ZipFile())
{
    zip.AddEntry("Readme.txt", stringContent1);
    zip.AddEntry("readings/Data.csv", stringContent2);
    zip.AddEntry("readings/Index.xml", stringContent3);
    zip.Save("Archive1.zip"); 
}

The code above assumes stringContent{1,2,3} contains the data to be stored in the files (or entries) in the zip archive. The first entry is "Readme.txt" and it is stored in the top level "Directory" in the zip archive. The next two entries are stored in the "readings" directory in the zip archive.

The strings are encoded in the default encoding. There is an overload of AddEntry(), not shown here, that allows you to explicitly specify the encoding to use.

If you have the content in a stream or byte array, not a string, there are overloads for AddEntry() that accept those types. There are also overloads that accept a Write delegate, a method of yours that is invoked to write data into the zip. This works for easily saving a DataSet into a zip file, for example.

DotNetZip is free and open source.

This function should create a byte array from a stream of data: I've created a simple interface for handling files for simplicity

public interface IHasDocumentProperties
{
    byte[] Content { get; set; }
    string Name { get; set; }
}

public void CreateZipFileContent(string filePath, IEnumerable<IHasDocumentProperties> fileInfos)
{    
    using (var memoryStream = new MemoryStream())
    {
        using (var zipArchive = new ZipArchive(memoryStream, ZipArchiveMode.Create, true))
        {
            foreach(var fileInfo in fileInfos)
            {
                var entry = zipArchive.CreateEntry(fileInfo.Name);

                using (var entryStream = entry.Open())
                {
                    entryStream.Write(fileInfo.Content, 0, fileInfo.Content.Length);
                }                        
            }
        }

        using (var fileStream = new FileStream(filePath, FileMode.OpenOrCreate, System.IO.FileAccess.Write))
        {
            memoryStream.CopyTo(fileStream);
        }
    }
}