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Connection Events

  • บทความ

All of the .NET Framework data providers have Connection objects with two events that you can use to retrieve informational messages from a data source or to determine if the state of a Connection has changed. The following table describes the events of the Connection object.

Event Description
InfoMessage Occurs when an informational message is returned from a data source. Informational messages are messages from a data source that do not result in an exception being thrown.
StateChange Occurs when the state of the Connection changes.

Working with the InfoMessage Event

You can retrieve warnings and informational messages from a SQL Server data source using the InfoMessage event of the SqlConnection object. Errors returned from the data source with a severity level of 11 through 16 cause an exception to be thrown. However, the InfoMessage event can be used to obtain messages from the data source that are not associated with an error. In the case of Microsoft SQL Server, any error with a severity of 10 or less is considered to be an informational message, and can be captured by using the InfoMessage event. For more information, see the Database Engine Error Severities article.

The InfoMessage event receives an SqlInfoMessageEventArgs object containing, in its Errors property, a collection of the messages from the data source. You can query the Error objects in this collection for the error number and message text, as well as the source of the error. The .NET Framework Data Provider for SQL Server also includes detail about the database, stored procedure, and line number that the message came from.

Example

The following code example shows how to add an event handler for the InfoMessage event.

' Assumes that connection represents a SqlConnection object.  
  AddHandler connection.InfoMessage, _  
    New SqlInfoMessageEventHandler(AddressOf OnInfoMessage)  
  
Private Shared Sub OnInfoMessage(sender As Object, _  
  args As SqlInfoMessageEventArgs)  
  Dim err As SqlError  
  For Each err In args.Errors  
    Console.WriteLine("The {0} has received a severity {1}, _  
       state {2} error number {3}\n" & _  
      "on line {4} of procedure {5} on server {6}:\n{7}", _  
      err.Source, err.Class, err.State, err.Number, err.LineNumber, _  
    err.Procedure, err.Server, err.Message)  
  Next  
End Sub  

// Assumes that connection represents a SqlConnection object.  
  connection.InfoMessage +=
    new SqlInfoMessageEventHandler(OnInfoMessage);  
  
protected static void OnInfoMessage(  
  object sender, SqlInfoMessageEventArgs args)  
{  
  foreach (SqlError err in args.Errors)  
  {  
    Console.WriteLine(  
  "The {0} has received a severity {1}, state {2} error number {3}\n" +  
  "on line {4} of procedure {5} on server {6}:\n{7}",  
   err.Source, err.Class, err.State, err.Number, err.LineNumber,
   err.Procedure, err.Server, err.Message);  
  }  
}

Handling Errors as InfoMessages

The InfoMessage event will normally fire only for informational and warning messages that are sent from the server. However, when an actual error occurs, the execution of the ExecuteNonQuery or ExecuteReader method that initiated the server operation is halted and an exception is thrown.

If you want to continue processing the rest of the statements in a command regardless of any errors produced by the server, set the FireInfoMessageEventOnUserErrors property of the SqlConnection to true. Doing this causes the connection to fire the InfoMessage event for errors instead of throwing an exception and interrupting processing. The client application can then handle this event and respond to error conditions.

Note

An error with a severity level of 17 or above that causes the server to stop processing the command must be handled as an exception. In this case, an exception is thrown regardless of how the error is handled in the InfoMessage event.

Working with the StateChange Event

The StateChange event occurs when the state of a Connection changes. The StateChange event receives StateChangeEventArgs that enable you to determine the change in state of the Connection by using the OriginalState and CurrentState properties. The OriginalState property is a ConnectionState enumeration that indicates the state of the Connection before it changed. CurrentState is a ConnectionState enumeration that indicates the state of the Connection after it changed.

The following code example uses the StateChange event to write a message to the console when the state of the Connection changes.

' Assumes connection represents a SqlConnection object.  
  AddHandler connection.StateChange, _  
    New StateChangeEventHandler(AddressOf OnStateChange)  
  
Protected Shared Sub OnStateChange( _  
  sender As Object, args As StateChangeEventArgs)  
  
  Console.WriteLine( _  
  "The current Connection state has changed from {0} to {1}.", _  
  args.OriginalState, args.CurrentState)  
End Sub  

// Assumes connection represents a SqlConnection object.  
  connection.StateChange  += new StateChangeEventHandler(OnStateChange);  
  
protected static void OnStateChange(object sender,
  StateChangeEventArgs args)  
{  
  Console.WriteLine(  
    "The current Connection state has changed from {0} to {1}.",  
      args.OriginalState, args.CurrentState);  
}

See also