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

Définition

Crée un Task<TResult> qui s'est terminé avec succès avec le résultat spécifié.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)

Paramètres de type

TResult

Type du résultat retourné par la tâche.The type of the result returned by the task.

Paramètres

result
TResult TResult TResult TResult

Résultat à enregistrer dans la tâche terminée.The result to store into the completed task.

Retours

Tâche terminée avec succès.The successfully completed task.

Exemples

L’exemple suivant est un utilitaire de ligne de commande qui calcule le nombre d’octets dans les fichiers dans chaque annuaire dont le nom est passé comme un argument de ligne de commande.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. Au lieu de l’exécution d’un plus long chemin d’accès de code qui instancie un FileStream de l’objet et récupère la valeur de son FileStream.Length propriété pour chaque fichier dans le répertoire, l’exemple appelle simplement la FromResult méthode pour créer une tâche dont Task<TResult>.Result propriété est zéro (0) si un répertoire ne comporte aucun fichier.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

Remarques

Cette méthode crée un Task<TResult> de l’objet dont la propriété Task<TResult>.Result propriété est result et dont Status propriété est RanToCompletion.This method creates a Task<TResult> object whose Task<TResult>.Result property is result and whose Status property is RanToCompletion. La méthode est couramment utilisée quand la valeur de retour d’une tâche est connue immédiatement sans exécuter un chemin d’accès du code plus long.The method is commonly used when the return value of a task is immediately known without executing a longer code path. Cet exemple en fournit une illustration.The example provides an illustration.

Pour créer un objet de tâche qui ne retourne pas de valeur, récupérer l’objet de tâche à partir de la CompletedTask propriété.To create a Task object that does not return a value, retrieve the Task object from the CompletedTask property.

S’applique à

Voir aussi