Process.ErrorDataReceived Event
Assembly: System (in system.dll)
'Declaration Public Event ErrorDataReceived As DataReceivedEventHandler 'Usage Dim instance As Process Dim handler As DataReceivedEventHandler AddHandler instance.ErrorDataReceived, handler
/** @event */ public void add_ErrorDataReceived (DataReceivedEventHandler value) /** @event */ public void remove_ErrorDataReceived (DataReceivedEventHandler value)
JScript supports the use of events, but not the declaration of new ones.
The ErrorDataReceived event indicates that the associated process has written to its redirected StandardError stream.
The event only occurs during asynchronous read operations on StandardError. To start asynchronous read operations, you must redirect the StandardError stream of a Process, add your event handler to the ErrorDataReceived event, and call BeginErrorReadLine. Thereafter, the ErrorDataReceived event signals each time the process writes a line to the redirected StandardError stream, until the process exits or calls CancelErrorRead.
The following example uses the net view command to list the available network resources on a remote computer. The user supplies the target computer name as a command-line argument. The user can also supply a file name for error output. The example collects the output of the net command, waits for the process to finish, and then writes the output results to the console. If the user supplies the optional error file, the example writes errors to the file.
' Define the namespaces used by this sample. Imports System Imports System.Text Imports System.Globalization Imports System.IO Imports System.Diagnostics Imports System.Threading Imports System.ComponentModel Imports Microsoft.VisualBasic Namespace ProcessAsyncStreamSamples Class ProcessAsyncErrorRedirection ' Define static variables shared by class methods. Private Shared streamError As StreamWriter = Nothing Private Shared netErrorFile As String = "" Private Shared netOutput As StringBuilder = Nothing Private Shared errorRedirect As Boolean = False Private Shared errorsWritten As Boolean = False Public Shared Sub RedirectNetCommandStreams() Dim netArguments As String Dim netProcess As Process ' Get the input computer name. Console.WriteLine("Enter the computer name for the net view command:") netArguments = Console.ReadLine().ToUpper(CultureInfo.InvariantCulture) If String.IsNullOrEmpty(netArguments) Then ' Default to the help command if there is ' not an input argument. netArguments = "/?" End If ' Check if errors should be redirected to a file. errorsWritten = False Console.WriteLine("Enter a fully qualified path to an error log file") Console.WriteLine(" or just press Enter to write errors to console:") netErrorFile = Console.ReadLine().ToUpper(CultureInfo.InvariantCulture) If Not String.IsNullOrEmpty(netErrorFile) Then errorRedirect = True End If ' Note that at this point, netArguments and netErrorFile ' are set with user input. If the user did not specify ' an error file, then errorRedirect is set to false. ' Initialize the process and its StartInfo properties. netProcess = New Process() netProcess.StartInfo.FileName = "Net.exe" ' Build the net command argument list. netProcess.StartInfo.Arguments = String.Format("view {0}", _ netArguments) ' Set UseShellExecute to false for redirection. netProcess.StartInfo.UseShellExecute = False ' Redirect the standard output of the net command. ' Read the stream asynchronously using an event handler. netProcess.StartInfo.RedirectStandardOutput = True AddHandler netProcess.OutputDataReceived, _ AddressOf NetOutputDataHandler netOutput = new StringBuilder() If errorRedirect Then ' Redirect the error output of the net command. netProcess.StartInfo.RedirectStandardError = True AddHandler netProcess.ErrorDataReceived, _ AddressOf NetErrorDataHandler Else ' Do not redirect the error output. netProcess.StartInfo.RedirectStandardError = False End If Console.WriteLine(ControlChars.Lf + "Starting process: NET {0}", _ netProcess.StartInfo.Arguments) If errorRedirect Then Console.WriteLine("Errors will be written to the file {0}", _ netErrorFile) End If ' Start the process. netProcess.Start() ' Start the asynchronous read of the standard output stream. netProcess.BeginOutputReadLine() If errorRedirect Then ' Start the asynchronous read of the standard ' error stream. netProcess.BeginErrorReadLine() End If ' Let the net command run, collecting the output. netProcess.WaitForExit() If Not streamError Is Nothing Then ' Close the error file. streamError.Close() Else ' Set errorsWritten to false if the stream is not ' open. Either there are no errors, or the error ' file could not be opened. errorsWritten = False End If If netOutput.Length > 0 Then ' If the process wrote more than just ' white space, write the output to the console. Console.WriteLine() Console.WriteLine("Public network shares from net view:") Console.WriteLine() Console.WriteLine(netOutput) Console.WriteLine() End If If errorsWritten Then ' Signal that the error file had something ' written to it. Dim errorOutput As String() errorOutput = File.ReadAllLines(netErrorFile) If errorOutput.Length > 0 Then Console.WriteLine(ControlChars.Lf + _ "The following error output was appended to {0}.", _ netErrorFile) Dim errLine as String For Each errLine in errorOutput Console.WriteLine(" {0}", errLine) Next Console.WriteLine() End If End If netProcess.Close() End Sub Private Shared Sub NetOutputDataHandler(sendingProcess As Object, _ outLine As DataReceivedEventArgs) ' Collect the net view command output. If Not String.IsNullOrEmpty(outLine.Data) Then ' Add the text to the collected output. netOutput.Append(Environment.NewLine + " " + outLine.Data) End If End Sub Private Shared Sub NetErrorDataHandler(sendingProcess As Object, _ errLine As DataReceivedEventArgs) ' Write the error text to the file if there is something to ' write and an error file has been specified. If Not String.IsNullOrEmpty(errLine.Data) Then If Not errorsWritten Then If streamError Is Nothing Then ' Open the file. Try streamError = New StreamWriter(netErrorFile, true) Catch e As Exception Console.WriteLine("Could not open error file!") Console.WriteLine(e.Message.ToString()) End Try End If If Not streamError Is Nothing Then ' Write a header to the file if this is the first ' call to the error output handler. streamError.WriteLine() streamError.WriteLine(DateTime.Now.ToString()) streamError.WriteLine("Net View error output:") End If errorsWritten = True End If If Not streamError Is Nothing Then ' Write redirected errors to the file. streamError.WriteLine(errLine.Data) streamError.Flush() End If End If End Sub End Class End Namespace
- SecurityPermission for calling members of Process. Demand value: LinkDemand; Named Permission Sets: FullTrust.
Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.