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DataReceivedEventArgs Class

Provides data for the OutputDataReceived and ErrorDataReceived events.

Namespace: System.Diagnostics
Assembly: System (in system.dll)

public class DataReceivedEventArgs : EventArgs
public class DataReceivedEventArgs extends EventArgs
public class DataReceivedEventArgs extends EventArgs
Not applicable.

To asynchronously collect the redirected StandardOutput or StandardError stream output of a process, you must create a method that handles the redirected stream output events. The event-handler method is called when the process writes to the redirected stream. The event delegate calls your event handler with an instance of DataReceivedEventArgs. The Data property contains the text line that the process wrote to the redirected stream.

The following code example illustrates how to perform asynchronous read operations on the redirected StandardOutput stream of the sort command. The sort command is a console application that reads and sorts text input.

The example creates an event delegate for the SortOutputHandler event handler and associates it with the OutputDataReceived event. The event handler receives text lines from the redirected StandardOutput stream, formats the text, and writes the text to the screen.

// Define the namespaces used by this sample.
using System;
using System.Text;
using System.IO;
using System.Diagnostics;
using System.Threading;
using System.ComponentModel;

namespace ProcessAsyncStreamSamples
{
    class SortOutputRedirection
    {
        // Define static variables shared by class methods.
        private static StringBuilder sortOutput = null;
        private static int numOutputLines = 0;
      
        public static void SortInputListText()
        {
            // Initialize the process and its StartInfo properties.
            // The sort command is a console application that
            // reads and sorts text input.

            Process sortProcess;
            sortProcess = new Process();
            sortProcess.StartInfo.FileName = "Sort.exe";
            
            // Set UseShellExecute to false for redirection.
            sortProcess.StartInfo.UseShellExecute = false;

            // Redirect the standard output of the sort command.  
            // This stream is read asynchronously using an event handler.
            sortProcess.StartInfo.RedirectStandardOutput = true;
            sortOutput = new StringBuilder("");

            // Set our event handler to asynchronously read the sort output.
            sortProcess.OutputDataReceived += new DataReceivedEventHandler(SortOutputHandler);

            // Redirect standard input as well.  This stream
            // is used synchronously.
            sortProcess.StartInfo.RedirectStandardInput = true;
  
            // Start the process.
            sortProcess.Start();

            // Use a stream writer to synchronously write the sort input.
            StreamWriter sortStreamWriter = sortProcess.StandardInput;

            // Start the asynchronous read of the sort output stream.
            sortProcess.BeginOutputReadLine();

            // Prompt the user for input text lines.  Write each 
            // line to the redirected input stream of the sort command.
            Console.WriteLine("Ready to sort up to 50 lines of text");

            String inputText;
            int numInputLines = 0;
            do 
            {
                Console.WriteLine("Enter a text line (or press the Enter key to stop):");
            
                inputText = Console.ReadLine();
                if (!String.IsNullOrEmpty(inputText))
                {
                    numInputLines ++;
                    sortStreamWriter.WriteLine(inputText);
                }
            }
            while (!String.IsNullOrEmpty(inputText) && (numInputLines < 50));
            Console.WriteLine("<end of input stream>");
            Console.WriteLine();

            // End the input stream to the sort command.
            sortStreamWriter.Close();

            // Wait for the sort process to write the sorted text lines.
            sortProcess.WaitForExit();

            if (numOutputLines > 0)
            {
                // Write the formatted and sorted output to the console.
                Console.WriteLine(" Sort results = {0} sorted text line(s) ", 
                    numOutputLines);
                Console.WriteLine("----------");
                Console.WriteLine(sortOutput);
            }
            else 
            {
                Console.WriteLine(" No input lines were sorted.");
            }

            sortProcess.Close();
        }

        private static void SortOutputHandler(object sendingProcess, 
            DataReceivedEventArgs outLine)
        {
            // Collect the sort command output.
            if (!String.IsNullOrEmpty(outLine.Data))
            {
                numOutputLines++;
    
                // Add the text to the collected output.
                sortOutput.Append(Environment.NewLine + 
                    "[" + numOutputLines.ToString() + "] - " + outLine.Data);
            }
        }
    }
}

System.Object
   System.EventArgs
    System.Diagnostics.DataReceivedEventArgs

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 98, Windows Server 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0

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