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Procédure : retourner une valeur à partir d’une tâche

  • Article

Cet exemple montre comment utiliser la classe System.Threading.Tasks.Task<TResult> pour retourner une valeur à partir de la propriété Result. Pour utiliser cet exemple, vous devez veiller à ce que le répertoire C:\Users\Public\Pictures\Sample Pictures existe et qu’il contienne des fichiers.

Exemple

using System;
using System.Linq;
using System.Threading.Tasks;

class Program
{
    static void Main()
    {
        // Return a value type with a lambda expression
        Task<int> task1 = Task<int>.Factory.StartNew(() => 1);
        int i = task1.Result;

        // Return a named reference type with a multi-line statement lambda.
        Task<Test> task2 = Task<Test>.Factory.StartNew(() =>
        {
            string s = ".NET";
            double d = 4.0;
            return new Test { Name = s, Number = d };
        });
        Test test = task2.Result;

        // Return an array produced by a PLINQ query
        Task<string[]> task3 = Task<string[]>.Factory.StartNew(() =>
        {
            string path = @"C:\Users\Public\Pictures\Sample Pictures\";
            string[] files = System.IO.Directory.GetFiles(path);

            var result = (from file in files.AsParallel()
                          let info = new System.IO.FileInfo(file)
                          where info.Extension == ".jpg"
                          select file).ToArray();

            return result;
        });

        foreach (var name in task3.Result)
            Console.WriteLine(name);
    }
    class Test
    {
        public string Name { get; set; }
        public double Number { get; set; }
    }
}

Imports System.Threading.Tasks

Module Module1

    Sub Main()
        ReturnAValue()

        Console.WriteLine("Press any key to exit.")
        Console.ReadKey()

    End Sub

    Sub ReturnAValue()

        ' Return a value type with a lambda expression
        Dim task1 = Task(Of Integer).Factory.StartNew(Function() 1)
        Dim i As Integer = task1.Result

        ' Return a named reference type with a multi-line statement lambda.
        Dim task2 As Task(Of Test) = Task.Factory.StartNew(Function()
                                                               Dim s As String = ".NET"
                                                               Dim d As Integer = 4
                                                               Return New Test With {.Name = s, .Number = d}
                                                           End Function)

        Dim myTest As Test = task2.Result
        Console.WriteLine(myTest.Name & ": " & myTest.Number)

        ' Return an array produced by a PLINQ query.
        Dim task3 As Task(Of String()) = Task(Of String()).Factory.StartNew(Function()

                                                                                Dim path = "C:\Users\Public\Pictures\Sample Pictures\"
                                                                                Dim files = System.IO.Directory.GetFiles(path)

                                                                                Dim result = (From file In files.AsParallel()
                                                                                              Let info = New System.IO.FileInfo(file)
                                                                                              Where info.Extension = ".jpg"
                                                                                              Select file).ToArray()
                                                                                Return result
                                                                            End Function)

        For Each name As String In task3.Result
            Console.WriteLine(name)
        Next
    End Sub

    Class Test
        Public Name As String
        Public Number As Double
    End Class
End Module

La propriété Result bloque le thread appelant jusqu'à ce que la tâche se termine.

Pour savoir comment passer le résultat d’une classe System.Threading.Tasks.Task<TResult> à une tâche de continuation, consultez Chaînage des tâches à l’aide de tâches de continuation.

Voir aussi