SqlCommand.BeginExecuteNonQuery Método

Definição

Inicia a execução assíncrona da instrução Transact-SQL ou procedimento armazenado que é descrito por este SqlCommand.Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand.

Sobrecargas

BeginExecuteNonQuery()

Inicia a execução assíncrona da instrução Transact-SQL ou procedimento armazenado que é descrito por este SqlCommand.Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand.

BeginExecuteNonQuery(AsyncCallback, Object)

Inicia a execução assíncrona da instrução Transact-SQL ou do procedimento armazenado descrito por esse SqlCommand, dado um procedimento de retorno de chamada e informações sobre o estado.Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand, given a callback procedure and state information.

BeginExecuteNonQuery()

Inicia a execução assíncrona da instrução Transact-SQL ou procedimento armazenado que é descrito por este SqlCommand.Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand.

public:
 IAsyncResult ^ BeginExecuteNonQuery();
public IAsyncResult BeginExecuteNonQuery ();
member this.BeginExecuteNonQuery : unit -> IAsyncResult
Public Function BeginExecuteNonQuery () As IAsyncResult

Retornos

IAsyncResult

Um IAsyncResult que pode ser usado para sondar ou aguardar resultados ou ambos. Esse valor também é necessário ao invocar EndExecuteNonQuery(IAsyncResult), que retorna o número de linhas afetadas.An IAsyncResult that can be used to poll or wait for results, or both; this value is also needed when invoking EndExecuteNonQuery(IAsyncResult), which returns the number of affected rows.

Exceções

Um SqlDbType diferente de Binary ou varbinary foi usado quando Value foi definido como Stream .A SqlDbType other than Binary or VarBinary was used when Value was set to Stream. Para saber mais sobre o streaming, consulte SqlClient Streaming Support (Suporte de streaming do SqlClient).For more information about streaming, see SqlClient Streaming Support.

- ou --or-

Um SqlDbType diferente de Char, nchar, nvarchar, varchar ou XML foi usado quando Value foi definido como TextReader .A SqlDbType other than Char, NChar, NVarChar, VarChar, or Xml was used when Value was set to TextReader.

- ou --or-

Um SqlDbType diferente de Xml foi usado quando Value foi definido como XmlReader.A SqlDbType other than Xml was used when Value was set to XmlReader.

Qualquer erro ocorrido ao executar o texto do comando.Any error that occurred while executing the command text.

- ou --or-

Ocorreu um tempo limite durante uma operação de streaming.A timeout occurred during a streaming operation. Para saber mais sobre o streaming, consulte SqlClient Streaming Support (Suporte de streaming do SqlClient).For more information about streaming, see SqlClient Streaming Support.

O par nome-valor "Asynchronous Processing=true" não foi incluído na cadeia de conexão que define a conexão para este SqlCommand.The name/value pair "Asynchronous Processing=true" was not included within the connection string defining the connection for this SqlCommand.

- ou --or-

O SqlConnection foi fechado ou removido durante uma operação de streaming.The SqlConnection closed or dropped during a streaming operation. Para saber mais sobre o streaming, consulte SqlClient Streaming Support (Suporte de streaming do SqlClient).For more information about streaming, see SqlClient Streaming Support.

Ocorreu um erro em um objeto Stream, XmlReader ou TextReader durante uma operação de streaming.An error occurred in a Stream, XmlReader or TextReader object during a streaming operation. Para saber mais sobre o streaming, consulte SqlClient Streaming Support (Suporte de streaming do SqlClient).For more information about streaming, see SqlClient Streaming Support.

O objeto Stream, XmlReader ou TextReader foi fechado durante uma operação de streaming.The Stream, XmlReader or TextReader object was closed during a streaming operation. Para saber mais sobre o streaming, consulte SqlClient Streaming Support (Suporte de streaming do SqlClient).For more information about streaming, see SqlClient Streaming Support.

Exemplos

O aplicativo de console a seguir cria dados de atualizações no banco de dado de exemplo AdventureWorks , fazendo seu trabalho de forma assíncrona.The following console application creates updates data within the AdventureWorks sample database, doing its work asynchronously. Para emular um processo de execução demorada, este exemplo insere uma instrução WAITFOR no texto do comando.In order to emulate a long-running process, this example inserts a WAITFOR statement in the command text. Normalmente, você não precisaria fazer com que os comandos funcionem mais lentamente, mas fazer isso neste caso facilita a demonstração do comportamento assíncrono.Normally, you would not take efforts to make your commands run slower, but doing this in this case makes it easier to demonstrate the asynchronous behavior.

using System.Data.SqlClient;

class Class1
{
    static void Main()
    {
        // This is a simple example that demonstrates the usage of the
        // BeginExecuteNonQuery functionality.
        // The WAITFOR statement simply adds enough time to prove the
        // asynchronous nature of the command.

        string commandText =
            "UPDATE Production.Product SET ReorderPoint = ReorderPoint + 1 " +
            "WHERE ReorderPoint Is Not Null;" +
            "WAITFOR DELAY '0:0:3';" +
            "UPDATE Production.Product SET ReorderPoint = ReorderPoint - 1 " +
            "WHERE ReorderPoint Is Not Null";

        RunCommandAsynchronously(commandText, GetConnectionString());

        Console.WriteLine("Press ENTER to continue.");
        Console.ReadLine();
    }

    private static void RunCommandAsynchronously(
        string commandText, string connectionString)
    {
        // Given command text and connection string, asynchronously execute
        // the specified command against the connection. For this example,
        // the code displays an indicator as it is working, verifying the
        // asynchronous behavior.
        using (SqlConnection connection =
                   new SqlConnection(connectionString))
        {
            try
            {
                int count = 0;
                SqlCommand command = new SqlCommand(commandText, connection);
                connection.Open();

                IAsyncResult result = command.BeginExecuteNonQuery();
                while (!result.IsCompleted)
                {
                    Console.WriteLine("Waiting ({0})", count++);
                    // Wait for 1/10 second, so the counter
                    // does not consume all available resources
                    // on the main thread.
                    System.Threading.Thread.Sleep(100);
                }
                Console.WriteLine("Command complete. Affected {0} rows.",
                    command.EndExecuteNonQuery(result));
            }
            catch (SqlException ex)
            {
                Console.WriteLine("Error ({0}): {1}", ex.Number, ex.Message);
            }
            catch (InvalidOperationException ex)
            {
                Console.WriteLine("Error: {0}", ex.Message);
            }
            catch (Exception ex)
            {
                // You might want to pass these errors
                // back out to the caller.
                Console.WriteLine("Error: {0}", ex.Message);
            }
        }
    }

    private static string GetConnectionString()
    {
        // To avoid storing the connection string in your code,
        // you can retrieve it from a configuration file.

        // If you have not included "Asynchronous Processing=true" in the
        // connection string, the command is not able
        // to execute asynchronously.
        return "Data Source=(local);Integrated Security=SSPI;" +
            "Initial Catalog=AdventureWorks; Asynchronous Processing=true";
    }
}
Imports System.Data.SqlClient

Module Module1

    Sub Main()
        ' This is a simple example that demonstrates the usage of the 
        ' BeginExecuteNonQuery functionality.
        ' The WAITFOR statement simply adds enough time to prove the 
        ' asynchronous nature of the command.
        Dim commandText As String = _
         "UPDATE Production.Product SET ReorderPoint = ReorderPoint + 1 " & _
         "WHERE ReorderPoint Is Not Null;" & _
         "WAITFOR DELAY '0:0:3';" & _
         "UPDATE Production.Product SET ReorderPoint = ReorderPoint - 1 " & _
         "WHERE ReorderPoint Is Not Null"

        RunCommandAsynchronously(commandText, GetConnectionString())

        Console.WriteLine("Press ENTER to continue.")
        Console.ReadLine()
    End Sub

    Private Sub RunCommandAsynchronously( _
     ByVal commandText As String, ByVal connectionString As String)

        ' Given command text and connection string, asynchronously execute
        ' the specified command against the connection. For this example,
        ' the code displays an indicator as it is working, verifying the 
        ' asynchronous behavior. 
        Using connection As New SqlConnection(connectionString)
            Try
                Dim count As Integer = 0
                Dim command As New SqlCommand(commandText, connection)
                connection.Open()
                Dim result As IAsyncResult = command.BeginExecuteNonQuery()
                While Not result.IsCompleted
                    Console.WriteLine("Waiting ({0})", count)
                    ' Wait for 1/10 second, so the counter
                    ' does not consume all available resources 
                    ' on the main thread.
                    Threading.Thread.Sleep(100)
                    count += 1
                End While
                Console.WriteLine("Command complete. Affected {0} rows.", _
                    command.EndExecuteNonQuery(result))
            Catch ex As SqlException
                Console.WriteLine("Error ({0}): {1}", ex.Number, ex.Message)
            Catch ex As InvalidOperationException
                Console.WriteLine("Error: {0}", ex.Message)
            Catch ex As Exception
                ' You might want to pass these errors
                ' back out to the caller.
                Console.WriteLine("Error: {0}", ex.Message)
            End Try
        End Using
    End Sub

    Private Function GetConnectionString() As String
        ' To avoid storing the connection string in your code,            
        ' you can retrieve it from a configuration file. 

        ' If you have not included "Asynchronous Processing=true" in the
        ' connection string, the command is not able
        ' to execute asynchronously.
        Return "Data Source=(local);Integrated Security=SSPI;" & _
          "Initial Catalog=AdventureWorks; Asynchronous Processing=true"
    End Function
End Module

Comentários

O BeginExecuteNonQuery método inicia o processo de execução assíncrona de uma instrução Transact-SQL ou um procedimento armazenado que não retorna linhas, para que outras tarefas possam ser executadas simultaneamente enquanto a instrução estiver em execução.The BeginExecuteNonQuery method starts the process of asynchronously executing a Transact-SQL statement or stored procedure that does not return rows, so that other tasks can run concurrently while the statement is executing. Quando a instrução for concluída, os desenvolvedores deverão chamar o EndExecuteNonQuery método para concluir a operação.When the statement has completed, developers must call the EndExecuteNonQuery method to finish the operation. O BeginExecuteNonQuery método retorna imediatamente, mas até que o código execute a EndExecuteNonQuery chamada de método correspondente, ele não deve executar nenhuma outra chamada que inicie uma execução síncrona ou assíncrona no mesmo SqlCommand objeto.The BeginExecuteNonQuery method returns immediately, but until the code executes the corresponding EndExecuteNonQuery method call, it must not execute any other calls that start a synchronous or asynchronous execution against the same SqlCommand object. Chamar o EndExecuteNonQuery antes da execução do comando é concluído faz com que o SqlCommand objeto seja bloqueado até que a execução seja concluída.Calling the EndExecuteNonQuery before the command's execution is completed causes the SqlCommand object to block until the execution is finished.

Observe que o texto e os parâmetros do comando são enviados para o servidor de forma síncrona.Note that the command text and parameters are sent to the server synchronously. Se um comando grande ou muitos parâmetros forem enviados, esse método poderá bloquear durante as gravações.If a large command or many parameters are sent, this method may block during writes. Depois que o comando é enviado, o método retorna imediatamente sem esperar por uma resposta do servidor, ou seja, leituras são assíncronas.After the command is sent, the method returns immediately without waiting for an answer from the server--that is, reads are asynchronous.

Como essa sobrecarga não dá suporte a um procedimento de retorno de chamada, os desenvolvedores devem sondar para determinar se o comando foi concluído, usando a IsCompleted Propriedade do IAsyncResult retornado pelo BeginExecuteNonQuery método ou aguardar a conclusão de um ou mais comandos usando a AsyncWaitHandle Propriedade do retornado IAsyncResult .Because this overload does not support a callback procedure, developers must either poll to determine whether the command has completed, using the IsCompleted property of the IAsyncResult returned by the BeginExecuteNonQuery method; or wait for the completion of one or more commands using the AsyncWaitHandle property of the returned IAsyncResult.

Esse método ignora a CommandTimeout propriedade.This method ignores the CommandTimeout property.

Aplica-se a

BeginExecuteNonQuery(AsyncCallback, Object)

Inicia a execução assíncrona da instrução Transact-SQL ou do procedimento armazenado descrito por esse SqlCommand, dado um procedimento de retorno de chamada e informações sobre o estado.Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand, given a callback procedure and state information.

public:
 IAsyncResult ^ BeginExecuteNonQuery(AsyncCallback ^ callback, System::Object ^ stateObject);
public IAsyncResult BeginExecuteNonQuery (AsyncCallback callback, object stateObject);
member this.BeginExecuteNonQuery : AsyncCallback * obj -> IAsyncResult
Public Function BeginExecuteNonQuery (callback As AsyncCallback, stateObject As Object) As IAsyncResult

Parâmetros

callback
AsyncCallback

Um delegado AsyncCallback invocado quando a execução do comando for concluída.An AsyncCallback delegate that is invoked when the command's execution has completed. Passe null (Nothing no Microsoft Visual Basic) para indicar que não é necessário um retorno de chamada.Pass null (Nothing in Microsoft Visual Basic) to indicate that no callback is required.

stateObject
Object

Um objeto de estado definido pelo usuário passado para o procedimento de retorno de chamada.A user-defined state object that is passed to the callback procedure. Recupere esse objeto de dentro do procedimento de retorno de chamada usando a propriedade AsyncState.Retrieve this object from within the callback procedure using the AsyncState property.

Retornos

IAsyncResult

Um IAsyncResult que pode ser usado para sondar ou aguardar resultados ou ambos. Esse valor também é necessário ao invocar EndExecuteNonQuery(IAsyncResult), que retorna o número de linhas afetadas.An IAsyncResult that can be used to poll or wait for results, or both; this value is also needed when invoking EndExecuteNonQuery(IAsyncResult), which returns the number of affected rows.

Exceções

Um SqlDbType diferente de Binary ou varbinary foi usado quando Value foi definido como Stream .A SqlDbType other than Binary or VarBinary was used when Value was set to Stream. Para saber mais sobre o streaming, consulte SqlClient Streaming Support (Suporte de streaming do SqlClient).For more information about streaming, see SqlClient Streaming Support.

- ou --or-

Um SqlDbType diferente de Char, nchar, nvarchar, varchar ou XML foi usado quando Value foi definido como TextReader .A SqlDbType other than Char, NChar, NVarChar, VarChar, or Xml was used when Value was set to TextReader.

- ou --or-

Um SqlDbType diferente de Xml foi usado quando Value foi definido como XmlReader.A SqlDbType other than Xml was used when Value was set to XmlReader.

Qualquer erro ocorrido ao executar o texto do comando.Any error that occurred while executing the command text.

- ou --or-

Ocorreu um tempo limite durante uma operação de streaming.A timeout occurred during a streaming operation. Para saber mais sobre o streaming, consulte SqlClient Streaming Support (Suporte de streaming do SqlClient).For more information about streaming, see SqlClient Streaming Support.

O par nome-valor "Asynchronous Processing=true" não foi incluído na cadeia de conexão que define a conexão para este SqlCommand.The name/value pair "Asynchronous Processing=true" was not included within the connection string defining the connection for this SqlCommand.

- ou --or-

O SqlConnection foi fechado ou removido durante uma operação de streaming.The SqlConnection closed or dropped during a streaming operation. Para saber mais sobre o streaming, consulte SqlClient Streaming Support (Suporte de streaming do SqlClient).For more information about streaming, see SqlClient Streaming Support.

Ocorreu um erro em um objeto Stream, XmlReader ou TextReader durante uma operação de streaming.An error occurred in a Stream, XmlReader or TextReader object during a streaming operation. Para saber mais sobre o streaming, consulte SqlClient Streaming Support (Suporte de streaming do SqlClient).For more information about streaming, see SqlClient Streaming Support.

O objeto Stream, XmlReader ou TextReader foi fechado durante uma operação de streaming.The Stream, XmlReader or TextReader object was closed during a streaming operation. Para saber mais sobre o streaming, consulte SqlClient Streaming Support (Suporte de streaming do SqlClient).For more information about streaming, see SqlClient Streaming Support.

Exemplos

O aplicativo do Windows a seguir demonstra o uso do BeginExecuteNonQuery método, executando uma instrução Transact-SQL que inclui um atraso de vários segundos (emulando um comando de longa execução).The following Windows application demonstrates the use of the BeginExecuteNonQuery method, executing a Transact-SQL statement that includes a delay of several seconds (emulating a long-running command).

Este exemplo demonstra muitas técnicas importantes.This example demonstrates many important techniques. Isso inclui chamar um método que interage com o formulário de um thread separado.This includes calling a method that interacts with the form from a separate thread. Além disso, este exemplo demonstra como você deve impedir que os usuários executem um comando várias vezes simultaneamente e como você deve certificar-se de que o formulário não é fechado antes de o procedimento de retorno de chamada ser chamado.In addition, this example demonstrates how you must block users from executing a command multiple times concurrently, and how you must make sure that the form does not close before the callback procedure is called.

Para configurar este exemplo, crie um aplicativo do Windows.To set up this example, create a new Windows application. Coloque um Button controle e um Label controle no formulário (aceitando o nome padrão de cada controle).Put a Button control and a Label control on the form (accepting the default name for each control). Adicione o código a seguir à classe do formulário, modificando a cadeia de conexão conforme necessário para o seu ambiente.Add the following code to the form's class, modifying the connection string as needed for your environment.

using System.Data.SqlClient;

namespace Microsoft.AdoDotNet.CodeSamples
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        // Hook up the form's Load event handler (you can double-click on
        // the form's design surface in Visual Studio), and then add
        // this code to the form's class:
        private void Form1_Load(object sender, EventArgs e)
        {
            this.button1.Click += new System.EventHandler(this.button1_Click);
            this.FormClosing += new System.Windows.Forms.
                FormClosingEventHandler(this.Form1_FormClosing);
        }

        // You need this delegate in order to display text from a thread
        // other than the form's thread. See the HandleCallback
        // procedure for more information.
        // This same delegate matches both the DisplayStatus
        // and DisplayResults methods.
        private delegate void DisplayInfoDelegate(string Text);

        // This flag ensures that the user does not attempt
        // to restart the command or close the form while the
        // asynchronous command is executing.
        private bool isExecuting;

        // This example maintains the connection object
        // externally, so that it is available for closing.
        private SqlConnection connection;

        private static string GetConnectionString()
        {
            // To avoid storing the connection string in your code,
            // you can retrieve it from a configuration file.

            // If you have not included "Asynchronous Processing=true" in the
            // connection string, the command is not able
            // to execute asynchronously.
            return "Data Source=(local);Integrated Security=true;" +
                "Initial Catalog=AdventureWorks; Asynchronous Processing=true";
        }

        private void DisplayStatus(string Text)
        {
            this.label1.Text = Text;
        }

        private void DisplayResults(string Text)
        {
            this.label1.Text = Text;
            DisplayStatus("Ready");
        }

        private void Form1_FormClosing(object sender,
            System.Windows.Forms.FormClosingEventArgs e)
        {
            if (isExecuting)
            {
                MessageBox.Show(this, "Cannot close the form until " +
                    "the pending asynchronous command has completed. Please wait...");
                e.Cancel = true;
            }
        }

        private void button1_Click(object sender, System.EventArgs e)
        {
            if (isExecuting)
            {
                MessageBox.Show(this,
                    "Already executing. Please wait until the current query " +
                    "has completed.");
            }
            else
            {
                SqlCommand command = null;
                try
                {
                    DisplayResults("");
                    DisplayStatus("Connecting...");
                    connection = new SqlConnection(GetConnectionString());
                    // To emulate a long-running query, wait for
                    // a few seconds before working with the data.
                    // This command does not do much, but that's the point--
                    // it does not change your data, in the long run.
                    string commandText =
                        "WAITFOR DELAY '0:0:05';" +
                        "UPDATE Production.Product SET ReorderPoint = ReorderPoint + 1 " +
                        "WHERE ReorderPoint Is Not Null;" +
                        "UPDATE Production.Product SET ReorderPoint = ReorderPoint - 1 " +
                        "WHERE ReorderPoint Is Not Null";

                    command = new SqlCommand(commandText, connection);
                    connection.Open();

                    DisplayStatus("Executing...");
                    isExecuting = true;
                    // Although it is not required that you pass the
                    // SqlCommand object as the second parameter in the
                    // BeginExecuteNonQuery call, doing so makes it easier
                    // to call EndExecuteNonQuery in the callback procedure.
                    AsyncCallback callback = new AsyncCallback(HandleCallback);
                    command.BeginExecuteNonQuery(callback, command);
                }
                catch (Exception ex)
                {
                    isExecuting = false;
                    DisplayStatus(string.Format("Ready (last error: {0})", ex.Message));
                    if (connection != null)
                    {
                        connection.Close();
                    }
                }
            }
        }

        private void HandleCallback(IAsyncResult result)
        {
            try
            {
                // Retrieve the original command object, passed
                // to this procedure in the AsyncState property
                // of the IAsyncResult parameter.
                SqlCommand command = (SqlCommand)result.AsyncState;
                int rowCount = command.EndExecuteNonQuery(result);
                string rowText = " rows affected.";
                if (rowCount == 1)
                {
                    rowText = " row affected.";
                }
                rowText = rowCount + rowText;

                // You may not interact with the form and its contents
                // from a different thread, and this callback procedure
                // is all but guaranteed to be running from a different thread
                // than the form. Therefore you cannot simply call code that
                // displays the results, like this:
                // DisplayResults(rowText)

                // Instead, you must call the procedure from the form's thread.
                // One simple way to accomplish this is to call the Invoke
                // method of the form, which calls the delegate you supply
                // from the form's thread.
                DisplayInfoDelegate del = new DisplayInfoDelegate(DisplayResults);
                this.Invoke(del, rowText);
            }
            catch (Exception ex)
            {
                // Because you are now running code in a separate thread,
                // if you do not handle the exception here, none of your other
                // code catches the exception. Because none of
                // your code is on the call stack in this thread, there is nothing
                // higher up the stack to catch the exception if you do not
                // handle it here. You can either log the exception or
                // invoke a delegate (as in the non-error case in this
                // example) to display the error on the form. In no case
                // can you simply display the error without executing a delegate
                // as in the try block here.

                // You can create the delegate instance as you
                // invoke it, like this:
                this.Invoke(new DisplayInfoDelegate(DisplayStatus),
                    String.Format("Ready(last error: {0}", ex.Message));
            }
            finally
            {
                isExecuting = false;
                if (connection != null)
                {
                    connection.Close();
                }
            }
        }
    }
}
Imports System.Data.SqlClient

Public Class Form1
    ' Add this code to the form's class:
    ' You need this delegate in order to display text from a thread
    ' other than the form's thread. See the HandleCallback
    ' procedure for more information.
    ' This same delegate matches both the DisplayStatus 
    ' and DisplayResults methods.
    Private Delegate Sub DisplayInfoDelegate(ByVal Text As String)

    ' This flag ensures that the user does not attempt
    ' to restart the command or close the form while the 
    ' asynchronous command is executing.
    Private isExecuting As Boolean

    ' This example maintains the connection object 
    ' externally, so that it is available for closing.
    Private connection As SqlConnection

    Private Function GetConnectionString() As String
        ' To avoid storing the connection string in your code,            
        ' you can retrieve it from a configuration file. 

        ' If you have not included "Asynchronous Processing=true" in the
        ' connection string, the command is not able
        ' to execute asynchronously.
        Return "Data Source=(local);Integrated Security=true;" & _
          "Initial Catalog=AdventureWorks; Asynchronous Processing=true"
    End Function

    Private Sub DisplayStatus(ByVal Text As String)
        Me.Label1.Text = Text
    End Sub

    Private Sub DisplayResults(ByVal Text As String)
        Me.Label1.Text = Text
        DisplayStatus("Ready")
    End Sub

    Private Sub Form1_FormClosing(ByVal sender As Object, _
        ByVal e As System.Windows.Forms.FormClosingEventArgs) _
        Handles Me.FormClosing
        If isExecuting Then
            MessageBox.Show(Me, "Cannot close the form until " & _
                "the pending asynchronous command has completed. Please wait...")
            e.Cancel = True
        End If
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles Button1.Click
        If isExecuting Then
            MessageBox.Show(Me, _
               "Already executing. Please wait until the current query " & _
                "has completed.")
        Else
            Dim command As SqlCommand
            Try
                DisplayResults("")
                DisplayStatus("Connecting...")
                connection = New SqlConnection(GetConnectionString())
                ' To emulate a long-running query, wait for 
                ' a few seconds before working with the data.
                ' This command does not do much, but that's the point--
                ' it does not change your data, in the long run.
                Dim commandText As String = _
                    "WAITFOR DELAY '0:0:05';" & _
                    "UPDATE Production.Product SET ReorderPoint = ReorderPoint + 1 " & _
                    "WHERE ReorderPoint Is Not Null;" & _
                    "UPDATE Production.Product SET ReorderPoint = ReorderPoint - 1 " & _
                    "WHERE ReorderPoint Is Not Null"

                command = New SqlCommand(commandText, connection)
                connection.Open()

                DisplayStatus("Executing...")
                isExecuting = True
                ' Although it is not required that you pass the 
                ' SqlCommand object as the second parameter in the 
                ' BeginExecuteNonQuery call, doing so makes it easier
                ' to call EndExecuteNonQuery in the callback procedure.
                Dim callback As New AsyncCallback(AddressOf HandleCallback)
                command.BeginExecuteNonQuery(callback, command)

            Catch ex As Exception
                isExecuting = False
                DisplayStatus(String.Format("Ready (last error: {0})", ex.Message))
                If connection IsNot Nothing Then
                    connection.Close()
                End If
            End Try
        End If
    End Sub

    Private Sub HandleCallback(ByVal result As IAsyncResult)
        Try
            ' Retrieve the original command object, passed
            ' to this procedure in the AsyncState property
            ' of the IAsyncResult parameter.
            Dim command As SqlCommand = CType(result.AsyncState, SqlCommand)
            Dim rowCount As Integer = command.EndExecuteNonQuery(result)
            Dim rowText As String = " rows affected."
            If rowCount = 1 Then
                rowText = " row affected."
            End If
            rowText = rowCount & rowText

            ' You may not interact with the form and its contents
            ' from a different thread, and this callback procedure
            ' is all but guaranteed to be running from a different thread
            ' than the form. Therefore you cannot simply call code that 
            ' displays the results, like this:
            ' DisplayResults(rowText)

            ' Instead, you must call the procedure from the form's thread.
            ' One simple way to accomplish this is to call the Invoke
            ' method of the form, which calls the delegate you supply
            ' from the form's thread. 
            Dim del As New DisplayInfoDelegate(AddressOf DisplayResults)
            Me.Invoke(del, rowText)

        Catch ex As Exception
            ' Because you are now running code in a separate thread, 
            ' if you do not handle the exception here, none of your other
            ' code catches the exception. Because none of your code
            ' is on the call stack in this thread, there is nothing
            ' higher up the stack to catch the exception if you do not 
            ' handle it here. You can either log the exception or 
            ' invoke a delegate (as in the non-error case in this 
            ' example) to display the error on the form. In no case
            ' can you simply display the error without executing a delegate
            ' as in the Try block here. 

            ' You can create the delegate instance as you 
            ' invoke it, like this:
            Me.Invoke(New DisplayInfoDelegate(AddressOf DisplayStatus), _
                String.Format("Ready(last error: {0}", ex.Message))
        Finally
            isExecuting = False
            If connection IsNot Nothing Then
                connection.Close()
            End If
        End Try
    End Sub
End Class

Comentários

O BeginExecuteNonQuery método inicia o processo de execução assíncrona de uma instrução Transact-SQL ou um procedimento armazenado que não retorna linhas, para que outras tarefas possam ser executadas simultaneamente enquanto a instrução estiver em execução.The BeginExecuteNonQuery method starts the process of asynchronously executing a Transact-SQL statement or stored procedure that does not return rows, so that other tasks can run concurrently while the statement is executing. Quando a instrução for concluída, os desenvolvedores deverão chamar o EndExecuteNonQuery método para concluir a operação.When the statement has completed, developers must call the EndExecuteNonQuery method to finish the operation. O BeginExecuteNonQuery método retorna imediatamente, mas até que o código execute a EndExecuteNonQuery chamada de método correspondente, ele não deve executar nenhuma outra chamada que inicie uma execução síncrona ou assíncrona no mesmo SqlCommand objeto.The BeginExecuteNonQuery method returns immediately, but until the code executes the corresponding EndExecuteNonQuery method call, it must not execute any other calls that start a synchronous or asynchronous execution against the same SqlCommand object. Chamar o EndExecuteNonQuery antes da execução do comando é concluído faz com que o SqlCommand objeto seja bloqueado até que a execução seja concluída.Calling the EndExecuteNonQuery before the command's execution is completed causes the SqlCommand object to block until the execution is finished.

O callback parâmetro permite especificar um AsyncCallback delegado que é chamado quando a instrução é concluída.The callback parameter lets you specify an AsyncCallback delegate that is called when the statement has completed. Você pode chamar o EndExecuteNonQuery método de dentro deste procedimento delegado ou de qualquer outro local dentro de seu aplicativo.You can call the EndExecuteNonQuery method from within this delegate procedure, or from any other location within your application. Além disso, você pode passar qualquer objeto no asyncStateObject parâmetro e o procedimento de retorno de chamada pode recuperar essas informações usando a AsyncState propriedade.In addition, you can pass any object in the asyncStateObject parameter, and your callback procedure can retrieve this information using the AsyncState property.

Observe que o texto e os parâmetros do comando são enviados para o servidor de forma síncrona.Note that the command text and parameters are sent to the server synchronously. Se um comando grande ou muitos parâmetros forem enviados, esse método poderá bloquear durante as gravações.If a large command or many parameters are sent, this method may block during writes. Depois que o comando é enviado, o método retorna imediatamente sem esperar por uma resposta do servidor, ou seja, leituras são assíncronas.After the command is sent, the method returns immediately without waiting for an answer from the server--that is, reads are asynchronous.

Como o procedimento de retorno de chamada é executado de dentro de um thread em segundo plano fornecido pelo Microsoft .NET Common Language Runtime, é muito importante que você adote uma abordagem rigorosa para lidar com interações entre threads de dentro de seus aplicativos.Because the callback procedure executes from within a background thread supplied by the Microsoft .NET common language runtime, it is very important that you take a rigorous approach to handling cross-thread interactions from within your applications. Por exemplo, você não deve interagir com o conteúdo de um formulário de dentro de seu procedimento de retorno de chamada; Se você precisar atualizar o formulário, deverá voltar para o thread do formulário para fazer seu trabalho.For example, you must not interact with a form's contents from within your callback procedure; should you have to update the form, you must switch back to the form's thread in order to do your work. O exemplo neste tópico demonstra esse comportamento.The example in this topic demonstrates this behavior.

Todos os erros que ocorrem durante a execução da operação são lançados como exceções no procedimento de retorno de chamada.All errors that occur during the execution of the operation are thrown as exceptions in the callback procedure. Você deve tratar a exceção no procedimento de retorno de chamada, não no aplicativo principal.You must handle the exception in the callback procedure, not in the main application. Consulte o exemplo neste tópico para obter informações adicionais sobre como tratar exceções no procedimento de retorno de chamada.See the example in this topic for additional information on handling exceptions in the callback procedure.

Esse método ignora a CommandTimeout propriedade.This method ignores the CommandTimeout property.

Aplica-se a