Windows apps
Collapse the table of content
Expand the table of content

TaskFactory.StartNew<TResult> Method (Func<TResult>)


Creates and starts a Task<TResult>.

Namespace:   System.Threading.Tasks
Assembly:  mscorlib (in mscorlib.dll)

public Task<TResult> StartNew<TResult>(
	Func<TResult> function


Type: System.Func<TResult>

A function delegate that returns the future result to be available through the Task<TResult>.

Return Value

Type: System.Threading.Tasks.Task<TResult>

The started Task<TResult>.

Type Parameters


The type of the result available through the Task<TResult>.

Exception Condition

The function argument is null.

Calling StartNew<TResult> is functionally equivalent to creating a Task<TResult> using one of its constructors and then calling Start to schedule it for execution.

Starting with the .NET Framework 4.5, you can call the Task.Run<TResult>(Func<TResult>) method as a quick way to call StartNew with default parameters. Note, however, that there is a difference in behavior between the two methods regarding : Task.Run<TResult>(Func<TResult>) by default does not allow child tasks started with the TaskCreationOptions.AttachedToParent option to attach to the current Task<TResult> instance, whereas StartNew<TResult>(Func<TResult>) does. For more information and code examples, see the entry Task.Run vs. Task.Factory.StartNew in the Parallel Programming with .NET blog.

The following example is a simple addition app that generates two random numbers and prompts the user to enter their sum. It then indicates whether the answer is correct or, if the user's response is not a valid number, prompts the user to re-enter a valid number. The StartNew<TResult> is used to create the Task<TResult> objects that return the random numbers to add.

using System;
using System.Threading.Tasks;

public class Example
   public static void Main()
      Random rnd = new Random();
      Task<int>[] tasks = new Task<int>[2];
      Object obj = new Object();

      while (true) {
         for (int ctr = 0; ctr <= 1; ctr++)
            tasks[ctr] = Task.Factory.StartNew(() => { int i = 0;
                                                       lock(obj) {
                                                          i = rnd.Next(101);
                                                       return i; });

         int n1 = tasks[0].Result;
         int n2 = tasks[1].Result;
         int result = n1 + n2;
         bool validInput = false;
         while (! validInput) {
            ShowMessage(n1, n2);
            string userInput = Console.ReadLine();
            // Process user input.
            if (userInput.Trim().ToUpper() == "X") return;
            int answer;
            validInput = Int32.TryParse(userInput, out answer);
            if (! validInput)
               Console.WriteLine("Invalid input. Try again, but enter only numbers. ");
            else if (answer == result)
               Console.WriteLine("Incorrect. The correct answer is {0}.", result);

   private static void ShowMessage(int n1, int n2)
      Console.WriteLine("\nEnter 'x' to exit...");
      Console.Write("{0} + {1} = ", n1, n2);
// The example displays the following output:
//       Enter 'x' to exit...
//       15 + 11 = 26
//       Correct!
//       Enter 'x' to exit...
//       75 + 33 = adc
//       Invalid input. Try again, but enter only numbers.
//       Enter 'x' to exit...
//       75 + 33 = 108
//       Correct!
//       Enter 'x' to exit...
//       67 + 55 = 133
//       Incorrect. The correct answer is 122.
//       Enter 'x' to exit...
//       92 + 51 = 133
//       Incorrect. The correct answer is 143.
//       Enter 'x' to exit...
//       81 + 65 = x

Universal Windows Platform
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Available since 5.0
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1
Return to top
© 2017 Microsoft