DeflateStream Constructor (Stream, CompressionMode, Boolean)


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Initializes a new instance of the DeflateStream class by using the specified stream and compression mode, and optionally leaves the stream open.

Namespace:   System.IO.Compression
Assembly:  System (in System.dll)

Public Sub New (
	stream As Stream,
	mode As CompressionMode,
	leaveOpen As Boolean


Type: System.IO.Stream

The stream to compress or decompress.

Type: System.IO.Compression.CompressionMode

One of the enumeration values that indicates whether to compress or decompress the stream.

Type: System.Boolean

true to leave the stream open after disposing the DeflateStream object; otherwise, false.

Exception Condition

stream is null.


mode is not a valid CompressionMode value.


CompressionMode is Compress and CanWrite is false.


CompressionMode is Decompress and CanRead is false.

By default, DeflateStream owns the underlying stream, so closing the stream also closes the underlying stream. Note that the state of the underlying stream can affect the usability of the stream. Also, no explicit checks are performed, so no additional exceptions are thrown when the new instance is created.

If an instance of the DeflateStream class is created with the mode parameter equal to Compress, header information is inserted immediately. If no further action occurs, the stream appears as a valid, empty, compressed file.

Using the DeflateStream class to compress a file larger than 4 GB raises an exception.

By default, the compression level is set to Optimal when the compression mode is Compress.

The following code example shows how to use the DeflateStream class to compress and decompress a file.

Imports System.IO
Imports System.IO.Compression

Public Class Program
    Shared directoryPath As String = "c:\temp"
    Public Shared Sub Main()

        Dim directorySelected As New DirectoryInfo(directoryPath)

        For Each fileToDecompress As FileInfo In directorySelected.GetFiles("*.cmp")
    End Sub

    Public Shared Sub Compress(directorySelected As DirectoryInfo)

        For Each file__1 As FileInfo In directorySelected.GetFiles("*.xml")
            Using originalFileStream As FileStream = file__1.OpenRead()
                If (File.GetAttributes(file__1.FullName) And FileAttributes.Hidden) <> FileAttributes.Hidden And file__1.Extension <> ".cmp" Then
                    Using compressedFileStream As FileStream = File.Create(file__1.FullName & ".cmp")
                        Using compressionStream As Compression.DeflateStream = New DeflateStream(compressedFileStream, CompressionMode.Compress)
                        End Using
                    End Using

                    Dim info As New FileInfo(directoryPath & "\" & file__1.Name & ".cmp")
                    Console.WriteLine("Compressed {0} from {1} to {2} bytes.", file__1.Name, file__1.Length, info.Length)
                End If
            End Using
    End Sub

    Public Shared Sub Decompress(fileToDecompress As FileInfo)
        Using originalFileStream As FileStream = fileToDecompress.OpenRead()
            Dim currentFileName As String = fileToDecompress.FullName
            Dim newFileName As String = currentFileName.Remove(currentFileName.Length - fileToDecompress.Extension.Length)

            Using decompressedFileStream As FileStream = File.Create(newFileName)
                Using decompressionStream As New DeflateStream(originalFileStream, CompressionMode.Decompress)
                    Console.WriteLine("Decompressed: {0}", fileToDecompress.Name)
                End Using
            End Using
        End Using
    End Sub
End Class

Universal Windows Platform
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Windows Phone
Available since 8.1
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