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Task.ContinueWith Method (Action<Task>, TaskContinuationOptions)

Creates a continuation that executes according to the specified TaskContinuationOptions.

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

public Task ContinueWith(
	Action<Task> continuationAction,
	TaskContinuationOptions continuationOptions


Type: System.Action<Task>
An action to run according to the specified continuationOptions. When run, the delegate will be passed the completed task as an argument.
Type: System.Threading.Tasks.TaskContinuationOptions
Options for when the continuation is scheduled and how it behaves. This includes criteria, such as OnlyOnCanceled, as well as execution options, such as ExecuteSynchronously.

Return Value

Type: System.Threading.Tasks.Task
A new continuation Task.


The Task has been disposed.


The continuationAction argument is null.


The continuationOptions argument specifies an invalid value for TaskContinuationOptions.

The returned Task will not be scheduled for execution until the current task has completed. If the continuation criteria specified through the continuationOptions parameter are not met, the continuation task will be canceled instead of scheduled.

The following example demonstrates using TaskContinuationOptions to specify that a continuation task should run synchronously when the antecedent task completes. (If the specified task has already completed by the time ContinueWith is called, the synchronous continuation will run on the thread calling ContinueWith.)

// C#

public class TaskCounter


private volatile int _count;

public void Track(Task t)


if (t == null) throw new ArgumentNullException("t");

Interlocked.Increment(ref _count);

t.ContinueWith(ct => Interlocked.Decrement(ref _count), TaskContinuationOptions.ExecuteSynchronously);


public int NumberOfActiveTasks { get { return _count; } }


' Visual Basic

Public Class TaskCounter

Private _count as Integer

Public Sub Track(ByVal t as Task)

If t is Nothing Then Throw New ArgumentNullException("t")




End Sub, TaskContinuationOptions.ExecuteSynchronously)

End Sub

Public ReadOnly Property NumberOfActiveTasks As Integer


Return _count

End Get

End Property

End Class

.NET Framework

Supported in: 4

.NET Framework Client Profile

Supported in: 4

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.