Task.ContinueWith<TResult> Method (Func<Task, TResult>, CancellationToken, TaskContinuationOptions, TaskScheduler)
Creates a continuation that executes according to the specified continuation options and returns a value. The continuation is passed a cancellation token and uses a specified scheduler.
Assembly: mscorlib (in mscorlib.dll)
public Task<TResult> ContinueWith<TResult>(
Func<Task, TResult> continuationFunction,
CancellationToken cancellationToken,
TaskContinuationOptions continuationOptions,
TaskScheduler scheduler
)
Parameters
- continuationFunction
-
Type:
System.Func<Task, TResult>
A function 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.
Type Parameters
- TResult
The type of the result produced by the continuation.
| Exception | Condition |
|---|---|
| ObjectDisposedException | The Task has been disposed. -or- The CancellationTokenSource that created the token has already been disposed. |
| ArgumentNullException | The continuationFunction argument is null. -or- The scheduler argument is null. |
| ArgumentOutOfRangeException | The continuationOptions argument specifies an invalid value for TaskContinuationOptions. |
The returned Task<TResult> 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 example shows how to use the ContinueWith method with continuation options:
using System; using System.Threading; using System.Threading.Tasks; class ContinuationOptionsDemo { // Demonstrated features: // TaskContinuationOptions // Task.ContinueWith() // Task.Factory // Task.Wait() // Expected results: // This sample demonstrates branched continuation sequences - Task+Commit or Task+Rollback. // Notice that no if statements are used. // The first sequence is successful - tran1 and commitTran1 are executed. rollbackTran1 is canceled. // The second sequence is unsuccessful - tran2 and rollbackTran2 are executed. tran2 is faulted, and commitTran2 is canceled. // Documentation: // http://msdn.microsoft.com/en-us/library/system.threading.tasks.taskcontinuationoptions(VS.100).aspx static void Main() { Action success = () => Console.WriteLine("Task={0}, Thread={1}: Begin successful transaction", Task.CurrentId, Thread.CurrentThread.ManagedThreadId); Action failure = () => { Console.WriteLine("Task={0}, Thread={1}: Begin transaction and encounter an error", Task.CurrentId, Thread.CurrentThread.ManagedThreadId); throw new InvalidOperationException("SIMULATED EXCEPTION"); }; Action<Task> commit = (antecendent) => Console.WriteLine("Task={0}, Thread={1}: Commit transaction", Task.CurrentId, Thread.CurrentThread.ManagedThreadId); Action<Task> rollback = (antecendent) => { // "Observe" your antecedent's exception so as to avoid an exception // being thrown on the finalizer thread var unused = antecendent.Exception; Console.WriteLine("Task={0}, Thread={1}: Rollback transaction", Task.CurrentId, Thread.CurrentThread.ManagedThreadId); }; // Successful transaction - Begin + Commit Console.WriteLine("Demonstrating a successful transaction"); // Initial task // Treated as "fire-and-forget" -- any exceptions will be cleaned up in rollback continuation Task tran1 = Task.Factory.StartNew(success); // The following task gets scheduled only if tran1 completes successfully var commitTran1 = tran1.ContinueWith(commit, TaskContinuationOptions.OnlyOnRanToCompletion); // The following task gets scheduled only if tran1 DOES NOT complete successfully var rollbackTran1 = tran1.ContinueWith(rollback, TaskContinuationOptions.NotOnRanToCompletion); // For demo purposes, wait for the sample to complete commitTran1.Wait(); // ----------------------------------------------------------------------------------- // Failed transaction - Begin + exception + Rollback Console.WriteLine("\nDemonstrating a failed transaction"); // Initial task // Treated as "fire-and-forget" -- any exceptions will be cleaned up in rollback continuation Task tran2 = Task.Factory.StartNew(failure); // The following task gets scheduled only if tran2 completes successfully var commitTran2 = tran2.ContinueWith(commit, TaskContinuationOptions.OnlyOnRanToCompletion); // The following task gets scheduled only if tran2 DOES NOT complete successfully var rollbackTran2 = tran2.ContinueWith(rollback, TaskContinuationOptions.NotOnRanToCompletion); // For demo purposes, wait for the sample to complete rollbackTran2.Wait(); } }
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