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

July 28, 2014

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,
	CancellationToken cancellationToken,
	TaskContinuationOptions continuationOptions,
	TaskScheduler scheduler
)

Parameters

continuationAction
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.
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.

ExceptionCondition
ObjectDisposedException

The Task has been disposed.

-or-

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.

// C#

private void Button1_Click(object sender, EventArgs e)

{

var backgroundScheduler = TaskScheduler.Default;

var uiScheduler = TaskScheduler.FromCurrentSynchronizationContext();

Task.Factory.StartNew(delegate { DoBackgroundComputation(); }, backgroundScheduler).

ContinueWith(delegate { UpdateUI(); }, uiScheduler).

ContinueWith(delegate { DoAnotherBackgroundComputation(); }, backgroundScheduler).

ContinueWith(delegate { UpdateUIAgain(); }, uiScheduler);

}

' Visual Basic

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

Windows Phone OS

Supported in: 8.1, 8.0

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