Task<TResult> Class

Definition

Represents an asynchronous operation that can return a value.

public class Task<TResult> : System.Threading.Tasks.Task
Type Parameters
TResult

The type of the result produced by this Task<TResult>.

Inheritance
Task<TResult>

Remarks

The Task<TResult> class represents a single operation that returns a value and that usually executes asynchronously. Task<TResult> objects are one of the central components of the task-based asynchronous pattern first introduced in the .NET Framework 4. Because the work performed by a Task<TResult> object typically executes asynchronously on a thread pool thread rather than synchronously on the main application thread, you can use the Status property, as well as the IsCanceled, IsCompleted, and IsFaulted properties, to determine the state of a task. Most commonly, a lambda expression is used to specify the work that the task is to perform.

Task<TResult> instances may be created in a variety of ways. The most common approach, which is available starting with the .NET Framework 4.5, is to call the static Task.Run<TResult>(Func<TResult>) or Task.Run<TResult>(Func<TResult>, CancellationToken) method. These methods provide a simple way to start a task by using default values and without acquiring additional parameters. The following example uses the Task.Run<TResult>(Func<TResult>) method to start a task that loops and then displays the number of loop iterations:

using System;
using System.Threading.Tasks;

public class Example
{
   public static void Main()
   {
      var t = Task<int>.Run( () => {
                                      // Just loop.
                                      int max = 1000000;
                                      int ctr = 0;
                                      for (ctr = 0; ctr <= max; ctr++) {
                                         if (ctr == max / 2 && DateTime.Now.Hour <= 12) {
                                            ctr++;
                                            break;
                                         }
                                      }
                                      return ctr;
                                    } );
      Console.WriteLine("Finished {0:N0} iterations.", t.Result);
   }
}
// The example displays output like the following:
//        Finished 1,000,001 loop iterations.
Imports System.Threading.Tasks

Module Example
   Public Sub Main()
      Dim t As Task(Of Integer) = Task.Run(Function()
                                  Dim max As Integer = 1000000
                                  Dim ctr As Integer
                                  For ctr = 0 to max
                                     If ctr = max \ 2 And Date.Now.Hour <= 12 Then
                                        ctr += 1
                                        Exit For
                                     End If
                                  Next
                                  Return ctr
                               End Function)
      Console.WriteLine("Finished {0:N0} iterations.", t.Result)
   End Sub
End Module
' The example displays the following output:
'       Finished 1,000,001 loop iterations

An alternative, and the most common way to start a task in the .NET Framework 4, is to call the static TaskFactory.StartNew or TaskFactory<TResult>.StartNew method. The Task.Factory property returns a TaskFactory object, and the Task<TResult>.Factory property returns a TaskFactory<TResult> object. Overloads of their StartNew method let you pass arguments, define task creation options, and specify a task scheduler. The following example uses the TaskFactory<TResult>.StartNew(Func<TResult>) method to start a task. It is functionally equivalent to the code in the previous example.

using System;
using System.Threading.Tasks;

public class Example
{
   public static void Main()
   {
      var t = Task<int>.Factory.StartNew( () => {
                                      // Just loop.
                                      int max = 1000000;
                                      int ctr = 0;
                                      for (ctr = 0; ctr <= max; ctr++) {
                                         if (ctr == max / 2 && DateTime.Now.Hour <= 12) {
                                            ctr++;
                                            break;
                                         }
                                      }
                                      return ctr;
                               } );
      Console.WriteLine("Finished {0:N0} iterations.", t.Result);
   }
}
// The example displays the following output:
//        Finished 1000001 loop iterations
Imports System.Threading.Tasks

Module Example
   Public Sub Main()
      Dim t = Task(Of Integer).Factory.StartNew(Function()
                                  Dim max As Integer = 1000000
                                  Dim ctr As Integer
                                  For ctr = 0 to max
                                     If ctr = max \ 2 And Date.Now.Hour <= 12 Then
                                       ctr += 1
                                       Exit For
                                     End If
                                  Next
                                  Return ctr
                               End Function)
      Console.WriteLine("Finished {0:N0} iterations.", t.Result)
   End Sub
End Module
' The example displays output like the following:
'       Finished 1,000,001 iterations

For more complete examples, see Task-based Asynchronous Programming.

The Task<TResult> class also provides constructors that initialize the task but that do not schedule it for execution. For performance reasons, the Task.Run and Task.Factory.StartNew methods are the preferred mechanisms for creating and scheduling computational tasks, but for scenarios where task creation and scheduling must be separated, the constructors may be used, and the task's Start method may then be used to schedule the task for execution at a later time.

Starting with desktop apps that target the .NET Framework 4.6, the culture of the thread that creates and invokes a task becomes part of the thread's context. That is, regardless of the current culture of the thread on which the task executes, the current culture of the task is the culture of the calling thread. For apps that target versions of the .NET Framework prior to the .NET Framework 4.6, the culture of the task is the culture of the thread on which the task executes. For more information, see the "Culture and task-based asynchronous operations" section in the CultureInfo topic. Note that Store apps follow the Windows Runtime in setting and getting the default culture.

For operations that do not return a value, you use the Task class. If you're developing with C# 7, for a more lightweight task that is a value type rather than a reference type, use the System.Threading.Tasks.ValueTask<TResult> structure; it is supported starting with C# 7.

Constructors

Task<TResult>(Func<TResult>)

Initializes a new Task<TResult> with the specified function.

Task<TResult>(Func<Object,TResult>, Object)

Initializes a new Task<TResult> with the specified function and state.

Task<TResult>(Func<TResult>, CancellationToken)

Initializes a new Task<TResult> with the specified function.

Task<TResult>(Func<TResult>, TaskCreationOptions)

Initializes a new Task<TResult> with the specified function and creation options.

Task<TResult>(Func<Object,TResult>, Object, CancellationToken)

Initializes a new Task<TResult> with the specified action, state, and options.

Task<TResult>(Func<Object,TResult>, Object, TaskCreationOptions)

Initializes a new Task<TResult> with the specified action, state, and options.

Task<TResult>(Func<TResult>, CancellationToken, TaskCreationOptions)

Initializes a new Task<TResult> with the specified function and creation options.

Task<TResult>(Func<Object,TResult>, Object, CancellationToken, TaskCreationOptions)

Initializes a new Task<TResult> with the specified action, state, and options.

Properties

Factory

Provides access to factory methods for creating and configuring Task<TResult> instances.

Result

Gets the result value of this Task<TResult>.

Methods

ConfigureAwait(Boolean)

Configures an awaiter used to await this Task<TResult>.

ContinueWith(Action<Task<TResult>,Object>, Object, CancellationToken, TaskContinuationOptions, TaskScheduler)

Creates a continuation that executes when the target Task<TResult> completes.

ContinueWith(Action<Task<TResult>>, CancellationToken, TaskContinuationOptions, TaskScheduler)

Creates a continuation that executes according the condition specified in continuationOptions.

ContinueWith(Action<Task<TResult>,Object>, Object, TaskScheduler)

Creates a continuation that executes when the target Task<TResult> completes.

ContinueWith(Action<Task<TResult>,Object>, Object, CancellationToken)

Creates a continuation that executes when the target Task<TResult> completes.

ContinueWith(Action<Task<TResult>,Object>, Object, TaskContinuationOptions)

Creates a continuation that executes when the target Task<TResult> completes.

ContinueWith(Action<Task<TResult>>, TaskContinuationOptions)

Creates a continuation that executes according the condition specified in continuationOptions.

ContinueWith(Action<Task<TResult>>, CancellationToken)

Creates a cancelable continuation that executes asynchronously when the target Task<TResult> completes.

ContinueWith(Action<Task<TResult>,Object>, Object)

Creates a continuation that that is passed state information and that executes when the target Task<TResult> completes.

ContinueWith(Action<Task<TResult>>)

Creates a continuation that executes asynchronously when the target task completes.

ContinueWith(Action<Task<TResult>>, TaskScheduler)

Creates a continuation that executes asynchronously when the target Task<TResult> completes.

ContinueWith<TNewResult>(Func<Task<TResult>,Object,TNewResult>, Object, CancellationToken, TaskContinuationOptions, TaskScheduler)

Creates a continuation that executes when the target Task<TResult> completes.

ContinueWith<TNewResult>(Func<Task<TResult>,TNewResult>, CancellationToken, TaskContinuationOptions, TaskScheduler)

Creates a continuation that executes according the condition specified in continuationOptions.

ContinueWith<TNewResult>(Func<Task<TResult>,Object,TNewResult>, Object, TaskScheduler)

Creates a continuation that executes when the target Task<TResult> completes.

ContinueWith<TNewResult>(Func<Task<TResult>,Object,TNewResult>, Object, TaskContinuationOptions)

Creates a continuation that executes when the target Task<TResult> completes.

ContinueWith<TNewResult>(Func<Task<TResult>,Object,TNewResult>, Object, CancellationToken)

Creates a continuation that executes when the target Task<TResult> completes.

ContinueWith<TNewResult>(Func<Task<TResult>,TNewResult>, TaskContinuationOptions)

Creates a continuation that executes according the condition specified in continuationOptions.

ContinueWith<TNewResult>(Func<Task<TResult>,TNewResult>, CancellationToken)

Creates a continuation that executes asynchronously when the target Task<TResult> completes.

ContinueWith<TNewResult>(Func<Task<TResult>,Object,TNewResult>, Object)

Creates a continuation that executes when the target Task<TResult> completes.

ContinueWith<TNewResult>(Func<Task<TResult>,TNewResult>)

Creates a continuation that executes asynchronously when the target Task<TResult> completes.

ContinueWith<TNewResult>(Func<Task<TResult>,TNewResult>, TaskScheduler)

Creates a continuation that executes asynchronously when the target Task<TResult> completes.

GetAwaiter()

Gets an awaiter used to await this Task<TResult>.

Equals(Object) Inherited from Object
Equals(Object, Object) Inherited from Object
GetHashCode() Inherited from Object
GetType() Inherited from Object
MemberwiseClone() Inherited from Object
ReferenceEquals(Object, Object) Inherited from Object
ToString() Inherited from Object
AsyncState Inherited from Task
CompletedTask Inherited from Task
ContinueWith(Action<Task,Object>, Object) Inherited from Task
ContinueWith(Action<Task,Object>, Object, CancellationToken) Inherited from Task
ContinueWith(Action<Task,Object>, Object, CancellationToken, TaskContinuationOptions, TaskScheduler) Inherited from Task
ContinueWith(Action<Task,Object>, Object, TaskContinuationOptions) Inherited from Task
ContinueWith(Action<Task,Object>, Object, TaskScheduler) Inherited from Task
ContinueWith(Action<Task>) Inherited from Task
ContinueWith(Action<Task>, CancellationToken) Inherited from Task
ContinueWith(Action<Task>, CancellationToken, TaskContinuationOptions, TaskScheduler) Inherited from Task
ContinueWith(Action<Task>, TaskContinuationOptions) Inherited from Task
ContinueWith(Action<Task>, TaskScheduler) Inherited from Task
ContinueWith<TResult>(Func<Task,TResult>) Inherited from Task
ContinueWith<TResult>(Func<Task,TResult>, CancellationToken) Inherited from Task
ContinueWith<TResult>(Func<Task,TResult>, CancellationToken, TaskContinuationOptions, TaskScheduler) Inherited from Task
ContinueWith<TResult>(Func<Task,TResult>, TaskContinuationOptions) Inherited from Task
ContinueWith<TResult>(Func<Task,TResult>, TaskScheduler) Inherited from Task
ContinueWith<TResult>(Func<Task,Object,TResult>, Object) Inherited from Task
ContinueWith<TResult>(Func<Task,Object,TResult>, Object, CancellationToken) Inherited from Task
ContinueWith<TResult>(Func<Task,Object,TResult>, Object, CancellationToken, TaskContinuationOptions, TaskScheduler) Inherited from Task
ContinueWith<TResult>(Func<Task,Object,TResult>, Object, TaskContinuationOptions) Inherited from Task
ContinueWith<TResult>(Func<Task,Object,TResult>, Object, TaskScheduler) Inherited from Task
CreationOptions Inherited from Task
CurrentId Inherited from Task
Delay(Int32) Inherited from Task
Delay(Int32, CancellationToken) Inherited from Task
Delay(TimeSpan) Inherited from Task
Delay(TimeSpan, CancellationToken) Inherited from Task
Dispose() Inherited from Task
Dispose(Boolean) Inherited from Task
Exception Inherited from Task
FromCanceled(CancellationToken) Inherited from Task
FromCanceled<TResult>(CancellationToken) Inherited from Task
FromException(Exception) Inherited from Task
FromException<TResult>(Exception) Inherited from Task
FromResult<TResult>(TResult) Inherited from Task
Id Inherited from Task
IsCanceled Inherited from Task
IsCompleted Inherited from Task
IsCompletedSuccessfully Inherited from Task
IsFaulted Inherited from Task
Run(Action) Inherited from Task
Run(Action, CancellationToken) Inherited from Task
Run(Func<Task>) Inherited from Task
Run(Func<Task>, CancellationToken) Inherited from Task
Run<TResult>(Func<TResult>) Inherited from Task
Run<TResult>(Func<TResult>, CancellationToken) Inherited from Task
Run<TResult>(Func<Task<TResult>>) Inherited from Task
Run<TResult>(Func<Task<TResult>>, CancellationToken) Inherited from Task
RunSynchronously() Inherited from Task
RunSynchronously(TaskScheduler) Inherited from Task
Start() Inherited from Task
Start(TaskScheduler) Inherited from Task
Status Inherited from Task
IAsyncResult.AsyncWaitHandle Inherited from Task
IAsyncResult.CompletedSynchronously Inherited from Task
Wait() Inherited from Task
Wait(Int32) Inherited from Task
Wait(Int32, CancellationToken) Inherited from Task
Wait(CancellationToken) Inherited from Task
Wait(TimeSpan) Inherited from Task
WaitAll(Task[]) Inherited from Task
WaitAll(Task[], Int32) Inherited from Task
WaitAll(Task[], Int32, CancellationToken) Inherited from Task
WaitAll(Task[], CancellationToken) Inherited from Task
WaitAll(Task[], TimeSpan) Inherited from Task
WaitAny(Task[]) Inherited from Task
WaitAny(Task[], Int32) Inherited from Task
WaitAny(Task[], Int32, CancellationToken) Inherited from Task
WaitAny(Task[], CancellationToken) Inherited from Task
WaitAny(Task[], TimeSpan) Inherited from Task
WhenAll(IEnumerable<Task>) Inherited from Task
WhenAll(Task[]) Inherited from Task
WhenAll<TResult>(IEnumerable<Task<TResult>>) Inherited from Task
WhenAll<TResult>(Task<TResult>[]) Inherited from Task
WhenAny(IEnumerable<Task>) Inherited from Task
WhenAny(Task[]) Inherited from Task
WhenAny<TResult>(IEnumerable<Task<TResult>>) Inherited from Task
WhenAny<TResult>(Task<TResult>[]) Inherited from Task
Yield() Inherited from Task

Extension Methods

Unwrap(Task<Task>)

Creates a proxy Task that represents the asynchronous operation of a TryExecuteTaskInline(Task, Boolean).

Unwrap<TResult>(Task<Task<TResult>>)

Creates a proxy Task that represents the asynchronous operation of a Task<Task<T>> (C#) or Task (Of Task(Of T)) (Visual Basic).

DispatcherOperationWait(Task)

Waits indefinitely for the underlying DispatcherOperation to complete.

DispatcherOperationWait(Task, TimeSpan)

Waits for the specified amount of time for the underlying DispatcherOperation to complete.

IsDispatcherOperationTask(Task)

Returns a value that indicates whether this Task is associated with a DispatcherOperation.

Applies to

Thread Safety

All members of Task<TResult>, except for Dispose(), are thread-safe and may be used from multiple threads concurrently.

See Also