Task.FromResult(TResult) Task.FromResult(TResult) Task.FromResult(TResult) Task.FromResult(TResult) Method

Definición

Crea un objeto Task<TResult> que se ha completado correctamente con el resultado especificado.Creates a Task<TResult> that's completed successfully with the specified result.

public:
generic <typename TResult>
 static System::Threading::Tasks::Task<TResult> ^ FromResult(TResult result);
public static System.Threading.Tasks.Task<TResult> FromResult<TResult> (TResult result);
static member FromResult : 'Result -> System.Threading.Tasks.Task<'Result>
Public Shared Function FromResult(Of TResult) (result As TResult) As Task(Of TResult)

Parámetros de tipo

TResult

Tipo de resultado devuelto por la tarea.The type of the result returned by the task.

Parámetros

result
TResult TResult TResult TResult

El resultado que se va a almacenar en la tarea completada.The result to store into the completed task.

Devoluciones

Tarea completada correctamente.The successfully completed task.

Ejemplos

El ejemplo siguiente es una utilidad de línea de comandos que calcula el número de bytes en los archivos en cada directorio cuyo nombre se pasa como un argumento de línea de comandos.The following example is a command-line utility that calculates the number of bytes in the files in each directory whose name is passed as a command-line argument. En lugar de ejecutar una ruta más larga de código que crea una instancia de un FileStream objeto y recupera el valor de su FileStream.Length propiedad para cada archivo en el directorio, el ejemplo se llama simplemente el FromResult método para crear una tarea cuya Task<TResult>.Result propiedad es cero (0) si un directorio no tiene ningún archivo.Rather than executing a longer code path that instantiates a FileStream object and retrieves the value of its FileStream.Length property for each file in the directory, the example simply calls the FromResult method to create a task whose Task<TResult>.Result property is zero (0) if a directory has no files.

using System;
using System.Collections.Generic;
using System.IO;
using System.Threading;
using System.Threading.Tasks;

public class Example
{
   public static void Main()
   {
      string[] args = Environment.GetCommandLineArgs();
      if (args.Length > 1) {
         List<Task<long>> tasks = new List<Task<long>>();
         for (int ctr = 1; ctr < args.Length; ctr++)
            tasks.Add(GetFileLengthsAsync(args[ctr]));

         try {
            Task.WaitAll(tasks.ToArray());
         }
         // Ignore exceptions here.
         catch (AggregateException) {}

         for (int ctr = 0 ; ctr < tasks.Count; ctr++) {
            if (tasks[ctr].Status == TaskStatus.Faulted)
               Console.WriteLine("{0} does not exist", args[ctr + 1]);
            else
               Console.WriteLine("{0:N0} bytes in files in '{1}'",
                                 tasks[ctr].Result, args[ctr + 1]);
         }
      }
      else {
         Console.WriteLine("Syntax error: Include one or more file paths.");
      }
   }

   private static Task<long> GetFileLengthsAsync(string filePath)
   {
      if (! Directory.Exists(filePath)) {
         return Task.FromException<long>(
                     new DirectoryNotFoundException("Invalid directory name."));
      }
      else {
         string[] files = Directory.GetFiles(filePath);
         if (files.Length == 0)
            return Task.FromResult(0L);
         else
            return Task.Run( () => { long total = 0;
                                     Parallel.ForEach(files, (fileName) => {
                                                 var fs = new FileStream(fileName, FileMode.Open,
                                                                         FileAccess.Read, FileShare.ReadWrite,
                                                                         256, true);
                                                 long length = fs.Length;
                                                 Interlocked.Add(ref total, length);
                                                 fs.Close(); } );
                                     return total;
                                   } );
      }
   }
}
// When launched with the following command line arguments:
//      subdir . newsubdir
// the example displays output like the following:
//       0 bytes in files in 'subdir'
//       2,059 bytes in files in '.'
//       newsubdir does not exist
Imports System.Collections.Generic
Imports System.IO
Imports System.Threading
Imports System.Threading.Tasks

Module Example
   Public Sub Main()
      Dim args() As String = Environment.GetCommandLineArgs()
      If args.Length > 1 Then
         Dim tasks As New List(Of Task(Of Long))
         For ctr = 1 To args.Length - 1
            tasks.Add(GetFileLengthsAsync(args(ctr)))
         Next
         Try
            Task.WaitAll(tasks.ToArray())
         ' Ignore exceptions here.
         Catch e As AggregateException
         End Try

         For ctr As Integer = 0 To tasks.Count - 1
            If tasks(ctr).Status = TaskStatus.Faulted Then
               Console.WriteLine("{0} does not exist", args(ctr + 1))
            Else
               Console.WriteLine("{0:N0} bytes in files in '{1}'",
                                 tasks(ctr).Result, args(ctr + 1))
            End If
         Next
      Else
         Console.WriteLine("Syntax error: Include one or more file paths.")
      End If
   End Sub
   
   Private Function GetFileLengthsAsync(filePath As String) As Task(Of Long)
      If Not Directory.Exists(filePath) Then
         Return Task.FromException(Of Long)(
                     New DirectoryNotFoundException("Invalid directory name."))
      Else
         Dim files As String() = Directory.GetFiles(filePath)
         If files.Length = 0 Then
            Return Task.FromResult(0L)
         Else
            Return Task.Run( Function()
                                Dim total As Long = 0
                                Dim lockObj As New Object
                                Parallel.ForEach(files, Sub(fileName)
                                                           Dim fs As New FileStream(fileName, FileMode.Open,
                                                                     FileAccess.Read, FileShare.ReadWrite,
                                                                     256, True)
                                                           Dim length As Long = fs.Length
                                                           Interlocked.Add(total, length)
                                                           fs.Close()
                                                        End Sub)
                                Return total
                             End Function )
         End If
      End If
   End Function
End Module
' When launched with the following command line arguments:
'      subdir . newsubdir
' the example displays output like the following:
'       0 bytes in files in 'subdir'
'       2,059 bytes in files in '.'
'       newsubdir does not exist

Comentarios

Este método crea un Task<TResult> cuyo Task<TResult>.Result propiedad es result y cuyo Status propiedad es RanToCompletion.This method creates a Task<TResult> object whose Task<TResult>.Result property is result and whose Status property is RanToCompletion. El método se usa habitualmente cuando el valor devuelto de una tarea se conoce inmediatamente sin ejecutar una ruta más larga de código.The method is commonly used when the return value of a task is immediately known without executing a longer code path. En este ejemplo se ilustra.The example provides an illustration.

Para crear un objeto de tarea que no devuelve un valor, recupere el objeto de tarea desde el CompletedTask propiedad.To create a Task object that does not return a value, retrieve the Task object from the CompletedTask property.

Se aplica a

Consulte también: