How to: Return a Value from a Task
This example shows how to use the System.Threading.Tasks.Task<TResult> type to return a value from the Result property.
Example
' How to: Return a Value from a Task
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 = 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 = 4.0
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
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; }
}
}
The Result property blocks the calling thread until the task finishes.
To see how to pass the result of one System.Threading.Tasks.Task<TResult> to a continuation task, see How to: Chain Multiple Tasks with Continuations
See Also
Concepts
Lambda Expressions in PLINQ and TPL