Process::OutputDataReceived Event
Occurs when an application writes to its redirected StandardOutput stream.
Assembly: System (in System.dll)
The OutputDataReceived event indicates that the associated Process has written to its redirected StandardOutput stream.
The event is enabled during asynchronous read operations on StandardOutput. To start asynchronous read operations, you must redirect the StandardOutput stream of a Process, add your event handler to the OutputDataReceived event, and call BeginOutputReadLine. Thereafter, the OutputDataReceived event signals each time the process writes a line to the redirected StandardOutput stream, until the process exits or calls CancelOutputRead.
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The application that is processing the asynchronous output should call the WaitForExit() method to ensure that the output buffer has been flushed. |
The following 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.dll> using namespace System; using namespace System::Text; using namespace System::IO; using namespace System::Diagnostics; using namespace System::Threading; using namespace System::ComponentModel; ref class SortOutputRedirection { private: // Define static variables shared by class methods. static StringBuilder^ sortOutput = nullptr; 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 = gcnew 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 = gcnew StringBuilder; // Set our event handler to asynchronously read the sort output. sortProcess->OutputDataReceived += gcnew 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.ToString() ); Console::WriteLine( "----------" ); Console::WriteLine( sortOutput->ToString() ); } 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->AppendFormat( "\n[{0}] {1}", numOutputLines.ToString(), outLine->Data ); } } }; /// The main entry point for the application. void main() { try { SortOutputRedirection::SortInputListText(); } catch ( InvalidOperationException^ e ) { Console::WriteLine( "Exception:" ); Console::WriteLine( e ); } }
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
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