GZipStream.BeginRead(Byte[], Int32, Int32, AsyncCallback, Object) Método

Definição

Inicia uma operação de leitura assíncrona.Begins an asynchronous read operation. (Considere o uso do método ReadAsync(Byte[], Int32, Int32) em seu lugar.)(Consider using the ReadAsync(Byte[], Int32, Int32) method instead.)

public:
 override IAsyncResult ^ BeginRead(cli::array <System::Byte> ^ array, int offset, int count, AsyncCallback ^ asyncCallback, System::Object ^ asyncState);
public:
 override IAsyncResult ^ BeginRead(cli::array <System::Byte> ^ buffer, int offset, int count, AsyncCallback ^ cback, System::Object ^ state);
public override IAsyncResult BeginRead (byte[] array, int offset, int count, AsyncCallback? asyncCallback, object? asyncState);
public override IAsyncResult BeginRead (byte[] array, int offset, int count, AsyncCallback asyncCallback, object asyncState);
public override IAsyncResult BeginRead (byte[] buffer, int offset, int count, AsyncCallback cback, object state);
override this.BeginRead : byte[] * int * int * AsyncCallback * obj -> IAsyncResult
override this.BeginRead : byte[] * int * int * AsyncCallback * obj -> IAsyncResult
Public Overrides Function BeginRead (array As Byte(), offset As Integer, count As Integer, asyncCallback As AsyncCallback, asyncState As Object) As IAsyncResult
Public Overrides Function BeginRead (buffer As Byte(), offset As Integer, count As Integer, cback As AsyncCallback, state As Object) As IAsyncResult

Parâmetros

arraybuffer
Byte[]

A matriz de bytes na qual os dados serão lidos.The byte array to read the data into.

offset
Int32

O deslocamento de bytes no array no qual será iniciada a leitura de dados no fluxo.The byte offset in array at which to begin reading data from the stream.

count
Int32

O número máximo de bytes a serem lidos.The maximum number of bytes to read.

asyncCallbackcback
AsyncCallback

Um retorno de chamada assíncrono opcional, a ser chamado quando a operação de leitura for concluída.An optional asynchronous callback, to be called when the read operation is complete.

asyncStatestate
Object

Um objeto fornecido pelo usuário que distingue essa solicitação de leitura assíncrona específica de outras solicitações.A user-provided object that distinguishes this particular asynchronous read request from other requests.

Retornos

IAsyncResult

Um objeto que representa a operação de leitura assíncrona, que ainda pode estar pendente.An object that represents the asynchronous read operation, which could still be pending.

Exceções

O método tentou fazer uma leitura assíncrona após o final do fluxo ou ocorreu um erro de disco.The method tried to read asynchronously past the end of the stream, or a disk error occurred.

Um ou mais argumentos são inválidos.One or more of the arguments is invalid.

Foram chamados métodos depois que o fluxo foi fechado.Methods were called after the stream was closed.

A implementação GZipStream atual não dá suporte à operação de leitura.The current GZipStream implementation does not support the read operation.

A operação de leitura não pode ser executada porque o fluxo está fechado.A read operation cannot be performed because the stream is closed.

Comentários

A partir do .NET Framework 4,5, você pode executar operações de leitura assíncronas usando o Stream.ReadAsync método.Starting with the .NET Framework 4.5, you can perform asynchronous read operations by using the Stream.ReadAsync method. O BeginRead método ainda está disponível no .NET Framework 4,5 para dar suporte ao código herdado; no entanto, você pode implementar operações de e/s assíncronas mais facilmente usando os novos métodos assíncronos.The BeginRead method is still available in .NET Framework 4.5 to support legacy code; however, you can implement asynchronous I/O operations more easily by using the new async methods. Para saber mais, confira E/S de arquivo assíncrona.For more information, see Asynchronous File I/O.

Passe o IAsyncResult valor de retorno para o EndRead método do fluxo para determinar quantos bytes foram lidos e para liberar os recursos do sistema operacional usados para leitura.Pass the IAsyncResult return value to the EndRead method of the stream to determine how many bytes were read and to release operating system resources used for reading. Isso pode ser feito usando o mesmo código chamado BeginRead ou em um retorno de chamada passado para BeginRead .You can do this either by using the same code that called BeginRead or in a callback passed to BeginRead.

A posição atual no fluxo é atualizada quando a leitura ou gravação assíncrona é emitida, não quando a operação de e/s é concluída.The current position in the stream is updated when the asynchronous read or write is issued, not when the I/O operation completes.

Várias solicitações assíncronas simultâneas tornam a ordem de conclusão da solicitação incerta.Multiple simultaneous asynchronous requests render the request completion order uncertain.

Use a CanRead propriedade para determinar se o GZipStream objeto atual oferece suporte à leitura.Use the CanRead property to determine whether the current GZipStream object supports reading.

Se um fluxo for fechado ou você passar um argumento inválido, as exceções serão geradas imediatamente do BeginRead .If a stream is closed or you pass an invalid argument, exceptions are thrown immediately from BeginRead. Os erros que ocorrem durante uma solicitação de leitura assíncrona, como uma falha de disco durante a solicitação de e/s, ocorrem no thread do pool de threads e geram exceções ao chamar EndRead .Errors that occur during an asynchronous read request, such as a disk failure during the I/O request, occur on the thread pool thread and throw exceptions when calling EndRead.

ExemplosExamples

O exemplo de código a seguir mostra como usar a GZipStream classe para compactar e descompactar um arquivo.The following code example shows how to use the GZipStream class to compress and decompress a file.

using System;
using System.IO;
using System.IO.Compression;

public class Program
{
    private static string directoryPath = @".\temp";
    public static void Main()
    {
        DirectoryInfo directorySelected = new DirectoryInfo(directoryPath);
        Compress(directorySelected);

        foreach (FileInfo fileToDecompress in directorySelected.GetFiles("*.gz"))
        {
            Decompress(fileToDecompress);
        }
    }

    public static void Compress(DirectoryInfo directorySelected)
    {
        foreach (FileInfo fileToCompress in directorySelected.GetFiles())
        {
            using (FileStream originalFileStream = fileToCompress.OpenRead())
            {
                if ((File.GetAttributes(fileToCompress.FullName) &
                   FileAttributes.Hidden) != FileAttributes.Hidden & fileToCompress.Extension != ".gz")
                {
                    using (FileStream compressedFileStream = File.Create(fileToCompress.FullName + ".gz"))
                    {
                        using (GZipStream compressionStream = new GZipStream(compressedFileStream,
                           CompressionMode.Compress))
                        {
                            originalFileStream.CopyTo(compressionStream);
                        }
                    }
                    FileInfo info = new FileInfo(directoryPath + Path.DirectorySeparatorChar + fileToCompress.Name + ".gz");
                    Console.WriteLine($"Compressed {fileToCompress.Name} from {fileToCompress.Length.ToString()} to {info.Length.ToString()} bytes.");
                }
            }
        }
    }

    public static void Decompress(FileInfo fileToDecompress)
    {
        using (FileStream originalFileStream = fileToDecompress.OpenRead())
        {
            string currentFileName = fileToDecompress.FullName;
            string newFileName = currentFileName.Remove(currentFileName.Length - fileToDecompress.Extension.Length);

            using (FileStream decompressedFileStream = File.Create(newFileName))
            {
                using (GZipStream decompressionStream = new GZipStream(originalFileStream, CompressionMode.Decompress))
                {
                    decompressionStream.CopyTo(decompressedFileStream);
                    Console.WriteLine($"Decompressed: {fileToDecompress.Name}");
                }
            }
        }
    }
}
Imports System.IO
Imports System.IO.Compression

Module Module1

    Private directoryPath As String = ".\temp"
    Public Sub Main()
        Dim directorySelected As New DirectoryInfo(directoryPath)
        Compress(directorySelected)

        For Each fileToDecompress As FileInfo In directorySelected.GetFiles("*.gz")
            Decompress(fileToDecompress)
        Next
    End Sub

    Public Sub Compress(directorySelected As DirectoryInfo)
        For Each fileToCompress As FileInfo In directorySelected.GetFiles()
            Using originalFileStream As FileStream = fileToCompress.OpenRead()
                If (File.GetAttributes(fileToCompress.FullName) And FileAttributes.Hidden) <> FileAttributes.Hidden And fileToCompress.Extension <> ".gz" Then
                    Using compressedFileStream As FileStream = File.Create(fileToCompress.FullName & ".gz")
                        Using compressionStream As New GZipStream(compressedFileStream, CompressionMode.Compress)

                            originalFileStream.CopyTo(compressionStream)
                        End Using
                    End Using
                    Dim info As New FileInfo(directoryPath & Path.DirectorySeparatorChar & fileToCompress.Name & ".gz")
                    Console.WriteLine($"Compressed {fileToCompress.Name} from {fileToCompress.Length.ToString()} to {info.Length.ToString()} bytes.")

                End If
            End Using
        Next
    End Sub


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

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

Aplica-se a