Task.ContinueWith Method (Action(Of Task), CancellationToken, TaskContinuationOptions, TaskScheduler)

 

Creates a continuation that executes when the target task competes according to the specified TaskContinuationOptions. The continuation receives a cancellation token and uses a specified scheduler.

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

Public Function ContinueWith (
	continuationAction As Action(Of Task),
	cancellationToken As CancellationToken,
	continuationOptions As TaskContinuationOptions,
	scheduler As TaskScheduler
) As Task

Parameters

continuationAction
Type: System.Action(Of Task)

An action to run according to the specified continuationOptions. When run, the delegate will be passed the completed task as an argument.

cancellationToken
Type: System.Threading.CancellationToken

The CancellationToken that will be assigned to the new continuation task.

continuationOptions
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.

scheduler
Type: System.Threading.Tasks.TaskScheduler

The TaskScheduler to associate with the continuation task and to use for its execution.

Return Value

Type: System.Threading.Tasks.Task

A new continuation Task.

Exception Condition
ObjectDisposedException

The CancellationTokenSource that created the token has already been disposed.

ArgumentNullException

The continuationAction argument is null.

-or-

The scheduler argument is null.

ArgumentOutOfRangeException

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 criteria specified through the continuationOptions parameter are not met, the continuation task will be canceled instead of scheduled.

The following is an example of using ContinueWith to run work both in the background and on the user interface threads.


Private Sub Button1_Click(ByVal sender As System.Object, 
                          ByVal e As System.EventArgs) Handles Button1.Click
   Dim backgroundScheduler = TaskScheduler.Default
   Dim uiScheduler = TaskScheduler.FromCurrentSynchronizationContext()

   Task.Factory.StartNew(Sub()
                           DoBackgroundComputation()
                         End Sub, backgroundScheduler).ContinueWith(Sub(t)
                            UpdateUI()
                         End Sub, uiScheduler).ContinueWith(Sub(t)
                            DoAnotherBackgroundComputation()
                         End Sub, backgroundScheduler).ContinueWith(Sub(t)
                            UpdateUIAgain()
                         End Sub, uiScheduler)
End Sub

Universal Windows Platform
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 5.0
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1
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