Cómo: Devolver un valor de una tareaHow to: Return a Value from a Task

En este ejemplo se muestra cómo se usa el tipo System.Threading.Tasks.Task<TResult> para devolver un valor de la propiedad Result.This example shows how to use the System.Threading.Tasks.Task<TResult> type to return a value from the Result property. Requiere que exista el directorio de C:\Usuarios\Pública\Imágenes\Imágenes de muestra\ y que contenga archivos.It requires that the C:\Users\Public\Pictures\Sample Pictures\ directory exists, and that it contains files.

EjemploExample

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 propiedad Result bloquea el subproceso que realiza la llamada hasta que la tarea finaliza.The Result property blocks the calling thread until the task finishes.

Para ver cómo se pasa el resultado de System.Threading.Tasks.Task<TResult> a una tarea de continuación, consulte Encadenar tareas mediante tareas de continuación.To see how to pass the result of one System.Threading.Tasks.Task<TResult> to a continuation task, see Chaining Tasks by Using Continuation Tasks.

Vea tambiénSee Also

Programación asincrónica basada en tareasTask-based Asynchronous Programming
Expresiones lambda en PLINQ y TPLLambda Expressions in PLINQ and TPL