DataTableReader.GetBytes(Int32, Int64, Byte[], Int32, Int32) Méthode

public:
 override long GetBytes(int ordinal, long dataIndex, cli::array <System::Byte> ^ buffer, int bufferIndex, int length);

public override long GetBytes(int ordinal, long dataIndex, byte[] buffer, int bufferIndex, int length);

override this.GetBytes : int * int64 * byte[] * int * int -> int64

Public Overrides Function GetBytes (ordinal As Integer, dataIndex As Long, buffer As Byte(), bufferIndex As Integer, length As Integer) As Long

Paramètres

Retours

Nombre réel d’octets lus.

Exceptions

Exemples

L’exemple suivant crée une DataTableReader base de données basée sur les données de l’exemple de base de données AdventureWorks et enregistre chaque image récupérée dans un fichier distinct dans le dossier C :\. Pour tester cette application, créez une application console, référencez l’assembly System.Drawing.dll et collez l’exemple de code dans le fichier nouvellement créé.

using System;
using System.Data.SqlClient;
using System.Data;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;

class Class1
{
    [STAThread]
    static void Main(string[] args)
    {
        TestGetBytes();
    }

    static private void TestGetBytes()
    {
        // Set up the data adapter, using information from
        // the AdventureWorks sample database.
        SqlDataAdapter photoAdapter = SetupDataAdapter(
            "SELECT ThumbnailPhotoFileName, ThumbNailPhoto " +
            "FROM Production.ProductPhoto");
        // Fill the DataTable.
        DataTable photoDataTable = new DataTable();
        photoAdapter.Fill(photoDataTable);

        using (DataTableReader reader = new DataTableReader(photoDataTable))
        {
            while (reader.Read())
            {
                String productName = null;
                try
                {
                    // Get the name of the file.
                    productName = reader.GetString(0);
                    // Get the length of the field. Pass null
                    // in the buffer parameter to retrieve the length
                    // of the data field. Ensure that the field isn't
                    // null before continuing.
                    if (reader.IsDBNull(1))
                    {
                        Console.WriteLine(productName + " is unavailable.");
                    }
                    else
                    {
                        long len = reader.GetBytes(1, 0, null, 0, 0);
                        // Create a buffer to hold the bytes, and then
                        // read the bytes from the DataTableReader.
                        Byte[] buffer = new Byte[len];
                        reader.GetBytes(1, 0, buffer, 0, (int)len);
                        // Create a new Bitmap object, passing the array
                        // of bytes to the constructor of a MemoryStream.
                        using (Bitmap productImage = new
                                   Bitmap(new MemoryStream(buffer)))
                        {
                            String fileName = "C:\\" + productName;
                            // Save in gif format.
                            productImage.Save(fileName, ImageFormat.Gif);
                            Console.WriteLine("Successfully created " + fileName);
                        }
                    }
                }
                catch (Exception ex)
                {
                    Console.WriteLine(productName + ": " + ex.Message);
                }
            }
        }
        Console.WriteLine("Press Enter to finish.");
        Console.ReadLine();
    }

    static private SqlDataAdapter SetupDataAdapter(String sqlString)
    {
        // Assuming all the default settings, create a SqlDataAdapter
        // working with the AdventureWorks sample database that's
        // available with SQL Server.
        String connectionString =
            "Data Source=(local);Initial Catalog=AdventureWorks;" +
            "Integrated Security=true";
        return new SqlDataAdapter(sqlString, connectionString);
    }
}

Imports System.Data
Imports System.Data.SqlClient
Imports System.Drawing
Imports System.IO
Imports System.Drawing.Imaging
    
Module Module1
   Sub Main()
      TestGetBytes()
   End Sub
   Private Sub TestGetBytes()
         ' Set up the data adapter, using information from 
      ' the AdventureWorks sample database.
      Dim photoAdapter As SqlDataAdapter = _
         SetupDataAdapter("SELECT ThumbnailPhotoFileName, " & _
         "ThumbNailPhoto FROM Production.ProductPhoto")

      ' Fill the DataTable.
      Dim photoDataTable As New DataTable
      photoAdapter.Fill(photoDataTable)

      ' Create the DataTableReader.
      Using reader As DataTableReader = New DataTableReader(photoDataTable)

         Dim buffer() As Byte
         Dim productName As String
         While reader.Read()
            Try
               ' Get the name of the file.
               productName = reader.GetString(0)

               ' Get the length of the field. Pass Nothing
               ' in the buffer parameter to retrieve the length
               ' of the data field. Ensure that the field isn't 
               ' null before continuing.
               If reader.IsDBNull(1) Then
                  Console.WriteLine( _
                     productName & " is unavailable.")
               Else
                  ' Retrieve the length of the necessary byte array.
                  Dim len As Long = reader.GetBytes(1, 0, Nothing, 0, 0)
                  ' Create a buffer to hold the bytes, and then 
                  ' read the bytes from the DataTableReader.
                  ReDim buffer(CInt(len))
                  reader.GetBytes(1, 0, buffer, 0, CInt(len))

                  ' Create a new Bitmap object, passing the array
                  ' of bytes to the constructor of a MemoryStream.
                  Using productImage As New Bitmap(New MemoryStream(buffer))
                     Dim fileName As String = "C:\" & productName
                     ' Save in gif format.
                     productImage.Save( _
                      fileName, ImageFormat.Gif)
                     Console.WriteLine("Successfully created " & _
                        fileName)
                  End Using
               End If
            Catch ex As Exception
               Console.WriteLine(productName & ": " & _
                  ex.Message)
            End Try
         End While
      End Using
      Console.WriteLine("Press Enter to finish.")
      Console.ReadLine()
   End Sub

   Private Function SetupDataAdapter( _
      ByVal sqlString As String) As SqlDataAdapter
      ' Assuming all the default settings, create a SqlDataAdapter
      ' working with the AdventureWorks sample database that's 
      ' available with SQL Server.
      Dim connectionString As String = _
         "Data Source=(local);" & _
         "Initial Catalog=AdventureWorks;" & _
         "Integrated Security=true"
      Return New SqlDataAdapter(sqlString, connectionString)
   End Function
End Module

Remarques

GetBytes retourne le nombre d’octets disponibles dans le champ. La plupart du temps, c’est la longueur exacte du champ. Toutefois, le nombre retourné peut être inférieur à la longueur réelle du champ s’il GetBytes a déjà été utilisé pour obtenir des octets à partir du champ. Il peut s’agir, par exemple, de la DataTableReader lecture d’une structure de données volumineuse dans une mémoire tampon

Si vous passez une mémoire tampon null (Nothing dans Visual Basic), GetBytes retourne la longueur du champ entier en octets, et non la taille restante en fonction du paramètre de décalage de mémoire tampon.

Aucune conversion n’est effectuée ; Par conséquent, les données récupérées doivent déjà être un tableau d’octets ou être coercibles dans un tableau d’octets.

Voir aussi

• GetChars(Int32, Int64, Char[], Int32, Int32)