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Task<TResult> Class

Represents an asynchronous operation that can return a value.

System.Object
  System.Threading.Tasks.Task
    System.Threading.Tasks.Task<TResult>

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

[DebuggerDisplayAttribute("Id = {Id}, Status = {Status}, Method = {DebuggerDisplayMethodDescription}, Result = {DebuggerDisplayResultDescription}")]
[HostProtectionAttribute(SecurityAction.LinkDemand, Synchronization = true, 
	ExternalThreading = true)]
public class Task<TResult> : Task

Type Parameters

TResult

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

The Task<TResult> type exposes the following members.

  NameDescription
Public methodSupported by Portable Class LibraryTask<TResult>(Func<TResult>)Initializes a new Task<TResult> with the specified function.
Public methodSupported by Portable Class LibraryTask<TResult>(Func<TResult>, CancellationToken)Initializes a new Task<TResult> with the specified function.
Public methodSupported by Portable Class LibraryTask<TResult>(Func<TResult>, TaskCreationOptions)Initializes a new Task<TResult> with the specified function and creation options.
Public methodSupported by Portable Class LibraryTask<TResult>(Func<Object, TResult>, Object)Initializes a new Task<TResult> with the specified function and state.
Public methodSupported by Portable Class LibraryTask<TResult>(Func<TResult>, CancellationToken, TaskCreationOptions)Initializes a new Task<TResult> with the specified function and creation options.
Public methodSupported by Portable Class LibraryTask<TResult>(Func<Object, TResult>, Object, CancellationToken)Initializes a new Task<TResult> with the specified action, state, and options.
Public methodSupported by Portable Class LibraryTask<TResult>(Func<Object, TResult>, Object, TaskCreationOptions)Initializes a new Task<TResult> with the specified action, state, and options.
Public methodSupported by Portable Class LibraryTask<TResult>(Func<Object, TResult>, Object, CancellationToken, TaskCreationOptions)Initializes a new Task<TResult> with the specified action, state, and options.
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  NameDescription
Public propertySupported by Portable Class LibraryAsyncStateGets the state object supplied when the Task was created, or null if none was supplied. (Inherited from Task.)
Public propertySupported by Portable Class LibraryCreationOptionsGets the TaskCreationOptions used to create this task. (Inherited from Task.)
Public propertySupported by Portable Class LibraryExceptionGets the AggregateException that caused the Task to end prematurely. If the Task completed successfully or has not yet thrown any exceptions, this will return null. (Inherited from Task.)
Public propertyStatic memberSupported by Portable Class LibraryFactoryProvides access to factory methods for creating and configuring Task<TResult> instances.
Public propertySupported by Portable Class LibraryIdGets a unique ID for this Task instance. (Inherited from Task.)
Public propertySupported by Portable Class LibraryIsCanceledGets whether this Task instance has completed execution due to being canceled. (Inherited from Task.)
Public propertySupported by Portable Class LibraryIsCompletedGets whether this Task has completed. (Inherited from Task.)
Public propertySupported by Portable Class LibraryIsFaultedGets whether the Task completed due to an unhandled exception. (Inherited from Task.)
Public propertySupported by Portable Class LibraryResultGets the result value of this Task<TResult>.
Public propertySupported by Portable Class LibraryStatusGets the TaskStatus of this task. (Inherited from Task.)
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  NameDescription
Public methodConfigureAwaitConfigures an awaiter used to await this Task<TResult>.
Public methodSupported by Portable Class LibraryContinueWith(Action<Task>)Creates a continuation that executes asynchronously when the target Task completes. (Inherited from Task.)
Public methodSupported by Portable Class LibraryContinueWith(Action<Task<TResult>>)Creates a continuation that executes asynchronously when the target task completes.
Public methodSupported by Portable Class LibraryContinueWith(Action<Task>, CancellationToken)Creates a continuation that executes asynchronously when the target Task completes. (Inherited from Task.)
Public methodSupported by Portable Class LibraryContinueWith(Action<Task>, TaskContinuationOptions)Creates a continuation that executes according to the specified TaskContinuationOptions. (Inherited from Task.)
Public methodSupported by Portable Class LibraryContinueWith(Action<Task>, TaskScheduler)Creates a continuation that executes asynchronously when the target Task completes. (Inherited from Task.)
Public methodContinueWith(Action<Task, Object>, Object)Creates a continuation that executes when the target Task completes. (Inherited from Task.)
Public methodSupported by Portable Class LibraryContinueWith(Action<Task<TResult>>, CancellationToken)Creates a cancelable continuation that executes asynchronously when the target Task<TResult> completes.
Public methodSupported by Portable Class LibraryContinueWith(Action<Task<TResult>>, TaskContinuationOptions)Creates a continuation that executes according the condition specified in continuationOptions.
Public methodSupported by Portable Class LibraryContinueWith(Action<Task<TResult>>, TaskScheduler)Creates a continuation that executes asynchronously when the target Task<TResult> completes.
Public methodContinueWith(Action<Task<TResult>, Object>, Object)Creates a continuation that executes when the target Task<TResult> completes.
Public methodContinueWith(Action<Task, Object>, Object, CancellationToken)Creates a continuation that executes when the target Task completes. (Inherited from Task.)
Public methodContinueWith(Action<Task, Object>, Object, TaskContinuationOptions)Creates a continuation that executes when the target Task completes. (Inherited from Task.)
Public methodContinueWith(Action<Task, Object>, Object, TaskScheduler)Creates a continuation that executes when the target Task completes. (Inherited from Task.)
Public methodContinueWith(Action<Task<TResult>, Object>, Object, CancellationToken)Creates a continuation that executes when the target Task<TResult> completes.
Public methodContinueWith(Action<Task<TResult>, Object>, Object, TaskContinuationOptions)Creates a continuation that executes when the target Task<TResult> completes.
Public methodContinueWith(Action<Task<TResult>, Object>, Object, TaskScheduler)Creates a continuation that executes when the target Task<TResult> completes.
Public methodSupported by Portable Class LibraryContinueWith(Action<Task>, CancellationToken, TaskContinuationOptions, TaskScheduler)Creates a continuation that executes according to the specified TaskContinuationOptions. (Inherited from Task.)
Public methodSupported by Portable Class LibraryContinueWith(Action<Task<TResult>>, CancellationToken, TaskContinuationOptions, TaskScheduler)Creates a continuation that executes according the condition specified in continuationOptions.
Public methodContinueWith(Action<Task, Object>, Object, CancellationToken, TaskContinuationOptions, TaskScheduler)Creates a continuation that executes when the target Task completes. (Inherited from Task.)
Public methodContinueWith(Action<Task<TResult>, Object>, Object, CancellationToken, TaskContinuationOptions, TaskScheduler)Creates a continuation that executes when the target Task<TResult> completes.
Public methodSupported by Portable Class LibraryContinueWith<TResult>(Func<Task, TResult>)Creates a continuation that executes asynchronously when the target Task completes. (Inherited from Task.)
Public methodSupported by Portable Class LibraryContinueWith<TNewResult>(Func<Task<TResult>, TNewResult>)Creates a continuation that executes asynchronously when the target Task<TResult> completes.
Public methodSupported by Portable Class LibraryContinueWith<TResult>(Func<Task, TResult>, CancellationToken)Creates a continuation that executes asynchronously when the target Task completes. (Inherited from Task.)
Public methodSupported by Portable Class LibraryContinueWith<TResult>(Func<Task, TResult>, TaskContinuationOptions)Creates a continuation that executes according to the condition specified in continuationOptions. (Inherited from Task.)
Public methodSupported by Portable Class LibraryContinueWith<TResult>(Func<Task, TResult>, TaskScheduler)Creates a continuation that executes asynchronously when the target Task completes. (Inherited from Task.)
Public methodContinueWith<TResult>(Func<Task, Object, TResult>, Object)Creates a continuation that executes when the target Task completes. (Inherited from Task.)
Public methodSupported by Portable Class LibraryContinueWith<TNewResult>(Func<Task<TResult>, TNewResult>, CancellationToken)Creates a continuation that executes asynchronously when the target Task<TResult> completes.
Public methodSupported by Portable Class LibraryContinueWith<TNewResult>(Func<Task<TResult>, TNewResult>, TaskContinuationOptions)Creates a continuation that executes according the condition specified in continuationOptions.
Public methodSupported by Portable Class LibraryContinueWith<TNewResult>(Func<Task<TResult>, TNewResult>, TaskScheduler)Creates a continuation that executes asynchronously when the target Task<TResult> completes.
Public methodContinueWith<TNewResult>(Func<Task<TResult>, Object, TNewResult>, Object)Creates a continuation that executes when the target Task<TResult> completes.
Public methodContinueWith<TResult>(Func<Task, Object, TResult>, Object, CancellationToken)Creates a continuation that executes when the target Task completes. (Inherited from Task.)
Public methodContinueWith<TResult>(Func<Task, Object, TResult>, Object, TaskContinuationOptions)Creates a continuation that executes when the target Task completes. (Inherited from Task.)
Public methodContinueWith<TResult>(Func<Task, Object, TResult>, Object, TaskScheduler)Creates a continuation that executes when the target Task completes. (Inherited from Task.)
Public methodContinueWith<TNewResult>(Func<Task<TResult>, Object, TNewResult>, Object, CancellationToken)Creates a continuation that executes when the target Task<TResult> completes.
Public methodContinueWith<TNewResult>(Func<Task<TResult>, Object, TNewResult>, Object, TaskContinuationOptions)Creates a continuation that executes when the target Task<TResult> completes.
Public methodContinueWith<TNewResult>(Func<Task<TResult>, Object, TNewResult>, Object, TaskScheduler)Creates a continuation that executes when the target Task<TResult> completes.
Public methodSupported by Portable Class LibraryContinueWith<TResult>(Func<Task, TResult>, CancellationToken, TaskContinuationOptions, TaskScheduler)Creates a continuation that executes according to the condition specified in continuationOptions. (Inherited from Task.)
Public methodSupported by Portable Class LibraryContinueWith<TNewResult>(Func<Task<TResult>, TNewResult>, CancellationToken, TaskContinuationOptions, TaskScheduler)Creates a continuation that executes according the condition specified in continuationOptions.
Public methodContinueWith<TResult>(Func<Task, Object, TResult>, Object, CancellationToken, TaskContinuationOptions, TaskScheduler)Creates a continuation that executes when the target Task completes. (Inherited from Task.)
Public methodContinueWith<TNewResult>(Func<Task<TResult>, Object, TNewResult>, Object, CancellationToken, TaskContinuationOptions, TaskScheduler)Creates a continuation that executes when the target Task<TResult> completes.
Public methodDispose()Releases all resources used by the current instance of the Task class. (Inherited from Task.)
Protected methodDispose(Boolean)Disposes the Task, releasing all of its unmanaged resources. (Inherited from Task.)
Public methodSupported by Portable Class LibraryEquals(Object)Determines whether the specified object is equal to the current object. (Inherited from Object.)
Protected methodSupported by Portable Class LibraryFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetAwaiterGets an awaiter used to await this Task<TResult>.
Public methodSupported by Portable Class LibraryGetHashCodeServes as the default hash function. (Inherited from Object.)
Public methodSupported by Portable Class LibraryGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodSupported by Portable Class LibraryMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodSupported by Portable Class LibraryRunSynchronously()Runs the Task synchronously on the current TaskScheduler. (Inherited from Task.)
Public methodSupported by Portable Class LibraryRunSynchronously(TaskScheduler)Runs the Task synchronously on the TaskScheduler provided. (Inherited from Task.)
Public methodSupported by Portable Class LibraryStart()Starts the Task, scheduling it for execution to the current TaskScheduler. (Inherited from Task.)
Public methodSupported by Portable Class LibraryStart(TaskScheduler)Starts the Task, scheduling it for execution to the specified TaskScheduler. (Inherited from Task.)
Public methodSupported by Portable Class LibraryToStringReturns a string that represents the current object. (Inherited from Object.)
Public methodSupported by Portable Class LibraryWait()Waits for the Task to complete execution. (Inherited from Task.)
Public methodSupported by Portable Class LibraryWait(CancellationToken)Waits for the Task to complete execution. The wait terminates if a cancellation token is canceled before the task completes. (Inherited from Task.)
Public methodSupported by Portable Class LibraryWait(Int32)Waits for the Task to complete execution within a specified number of milliseconds. (Inherited from Task.)
Public methodSupported by Portable Class LibraryWait(TimeSpan)Waits for the Task to complete execution within a specified time interval. (Inherited from Task.)
Public methodSupported by Portable Class LibraryWait(Int32, CancellationToken)Waits for the Task to complete execution. The wait terminates if a timeout interval elapses or a cancellation token is canceled before the task completes. (Inherited from Task.)
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  NameDescription
Public Extension MethodAsAsyncActionReturns a Windows Runtime asynchronous action that represents a started task. (Defined by WindowsRuntimeSystemExtensions.)
Public Extension MethodAsAsyncOperation<TResult>Returns a Windows Runtime asynchronous operation that represents a started task that returns a result. (Defined by WindowsRuntimeSystemExtensions.)
Public Extension MethodDispatcherOperationWait()Overloaded. Waits indefinitely for the underlying DispatcherOperation to complete. (Defined by TaskExtensions.)
Public Extension MethodDispatcherOperationWait(TimeSpan)Overloaded. Waits for the specified amount of time for the underlying DispatcherOperation to complete. (Defined by TaskExtensions.)
Public Extension MethodIsDispatcherOperationTaskReturns a value that indicates whether this Task is associated with a DispatcherOperation. (Defined by TaskExtensions.)
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  NameDescription
Explicit interface implemetationPrivate propertySupported by Portable Class LibraryIAsyncResult.AsyncWaitHandleGets a WaitHandle that can be used to wait for the task to complete. (Inherited from Task.)
Explicit interface implemetationPrivate propertySupported by Portable Class LibraryIAsyncResult.CompletedSynchronouslyGets an indication of whether the operation completed synchronously. (Inherited from Task.)
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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 programming pattern first introduced in the . 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.

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

For more complete examples, see Task Parallelism (Task Parallel Library).

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 StartNew methods are the preferred mechanism 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 apps that target the .NET Framework 4.6 Preview, 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 Preview, 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.

For operations that do not return a value, you use the Task class.

NoteNote

The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: Synchronization | ExternalThreading. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

.NET Framework

Supported in: 4.6, 4.5, 4

.NET Framework Client Profile

Supported in: 4

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8

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

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