Using WorkflowInvoker and WorkflowApplication
Windows Workflow Foundation (WF) provides several methods of hosting workflows. WorkflowInvoker provides a simple way for invoking a workflow as if it were a method call and can be used only for workflows that do not use persistence. WorkflowApplication provides a richer model for executing workflows that includes notification of lifecycle events, execution control, bookmark resumption, and persistence. WorkflowServiceHost provides support for messaging activities and is primarily used with workflow services. This topic introduces you to workflow hosting with WorkflowInvoker and WorkflowApplication. For more information about hosting workflows with WorkflowServiceHost, see Workflow Services and Hosting Workflow Services Overview.
Using WorkflowInvoker
WorkflowInvoker provides a model for executing a workflow as if it were a method call. To invoke a workflow using WorkflowInvoker, call the Invoke method and pass in the workflow definition of the workflow to invoke. In this example, a WriteLine activity is invoked using WorkflowInvoker.
Activity wf = new WriteLine
{
Text = "Hello World."
};
WorkflowInvoker.Invoke(wf);
When a workflow is invoked using WorkflowInvoker, the workflow executes on the calling thread and the Invoke method blocks until the workflow is complete, including any idle time. To configure a time-out interval in which the workflow must complete, use one of the Invoke overloads that takes a TimeSpan parameter. In this example, a workflow is invoked twice with two different time-out intervals. The first workflow completes, but the second does not.
Activity wf = new Sequence()
{
Activities =
{
new WriteLine()
{
Text = "Before the 1 minute delay."
},
new Delay()
{
Duration = TimeSpan.FromMinutes(1)
},
new WriteLine()
{
Text = "After the 1 minute delay."
}
}
};
// This workflow completes successfully.
WorkflowInvoker.Invoke(wf, TimeSpan.FromMinutes(2));
// This workflow does not complete and a TimeoutException
// is thrown.
try
{
WorkflowInvoker.Invoke(wf, TimeSpan.FromSeconds(30));
}
catch (TimeoutException ex)
{
Console.WriteLine(ex.Message);
}
Note
The TimeoutException is only thrown if the time-out interval elapses and the workflow becomes idle during execution. A workflow that takes longer than the specified time-out interval to complete completes successfully if the workflow does not become idle.
WorkflowInvoker also provides asynchronous versions of the invoke method. For more information, see InvokeAsync and BeginInvoke.
Setting Input Arguments of a Workflow
Data can be passed into a workflow using a dictionary of input parameters, keyed by argument name, that map to the input arguments of the workflow. In this example, a WriteLine is invoked and the value for its Text argument is specified using the dictionary of input parameters.
Activity wf = new WriteLine();
Dictionary<string, object> inputs = new Dictionary<string, object>();
inputs.Add("Text", "Hello World.");
WorkflowInvoker.Invoke(wf, inputs);
Retrieving Output Arguments of a Workflow
The output parameters of a workflow can be obtained using the outputs dictionary that is returned from the call to Invoke. The following example invokes a workflow consisting of a single Divide activity that has two input arguments and two output arguments. When the workflow is invoked, the arguments dictionary is passed which contains the values for each input argument, keyed by argument name. When the call to Invoke returns, each output argument is returned in the outputs dictionary, also keyed by argument name.
public sealed class Divide : CodeActivity
{
[RequiredArgument]
public InArgument<int> Dividend { get; set; }
[RequiredArgument]
public InArgument<int> Divisor { get; set; }
public OutArgument<int> Remainder { get; set; }
public OutArgument<int> Result { get; set; }
protected override void Execute(CodeActivityContext context)
{
int quotient = Dividend.Get(context) / Divisor.Get(context);
int remainder = Dividend.Get(context) % Divisor.Get(context);
Result.Set(context, quotient);
Remainder.Set(context, remainder);
}
}
int dividend = 500;
int divisor = 36;
Dictionary<string, object> arguments = new Dictionary<string, object>();
arguments.Add("Dividend", dividend);
arguments.Add("Divisor", divisor);
IDictionary<string, object> outputs =
WorkflowInvoker.Invoke(new Divide(), arguments);
Console.WriteLine("{0} / {1} = {2} Remainder {3}",
dividend, divisor, outputs["Result"], outputs["Remainder"]);
If the workflow derives from ActivityWithResult, such as CodeActivity<TResult> or Activity<TResult>, and there are output arguments in addition to the well-defined Result output argument, a non-generic overload of Invoke must be used in order to retrieve the additional arguments. To do this, the workflow definition passed into Invoke must be of type Activity. In this example the Divide activity derives from CodeActivity<int>, but is declared as Activity so that a non-generic overload of Invoke is used which returns a dictionary of arguments instead of a single return value.
public sealed class Divide : CodeActivity<int>
{
public InArgument<int> Dividend { get; set; }
public InArgument<int> Divisor { get; set; }
public OutArgument<int> Remainder { get; set; }
protected override int Execute(CodeActivityContext context)
{
int quotient = Dividend.Get(context) / Divisor.Get(context);
int remainder = Dividend.Get(context) % Divisor.Get(context);
Remainder.Set(context, remainder);
return quotient;
}
}
int dividend = 500;
int divisor = 36;
Dictionary<string, object> arguments = new Dictionary<string, object>();
arguments.Add("Dividend", dividend);
arguments.Add("Divisor", divisor);
Activity wf = new Divide();
IDictionary<string, object> outputs =
WorkflowInvoker.Invoke(wf, arguments);
Console.WriteLine("{0} / {1} = {2} Remainder {3}",
dividend, divisor, outputs["Result"], outputs["Remainder"]);
Using WorkflowApplication
WorkflowApplication provides a rich set of features for workflow instance management. WorkflowApplication acts as a thread safe proxy to the actual WorkflowInstance, which encapsulates the runtime, and provides methods for creating and loading workflow instances, pausing and resuming, terminating, and notification of lifecycle events. To run a workflow using WorkflowApplication you create the WorkflowApplication, subscribe to any desired lifecycle events, start the workflow, and then wait for it to finish. In this example, a workflow definition that consists of a WriteLine activity is created and a WorkflowApplication is created using the specified workflow definition. Completed is handled so the host is notified when the workflow completes, the workflow is started with a call to Run, and then the host waits for the workflow to complete. When the workflow completes, the AutoResetEvent is set and the host application can resume execution, as shown in the following example.
AutoResetEvent syncEvent = new AutoResetEvent(false);
Activity wf = new WriteLine
{
Text = "Hello World."
};
// Create the WorkflowApplication using the desired
// workflow definition.
WorkflowApplication wfApp = new WorkflowApplication(wf);
// Handle the desired lifecycle events.
wfApp.Completed = delegate (WorkflowApplicationCompletedEventArgs e)
{
syncEvent.Set();
};
// Start the workflow.
wfApp.Run();
// Wait for Completed to arrive and signal that
// the workflow is complete.
syncEvent.WaitOne();
WorkflowApplication Lifecycle Events
In addition to Completed, host authors can be notified when a workflow is unloaded (Unloaded), aborted (Aborted), becomes idle (Idle and PersistableIdle), or an unhandled exception occurs (OnUnhandledException). Workflow application developers can handle these notifications and take appropriate action, as shown in the following example.
wfApp.Completed = delegate (WorkflowApplicationCompletedEventArgs e)
{
if (e.CompletionState == ActivityInstanceState.Faulted)
{
Console.WriteLine("Workflow {0} Terminated.", e.InstanceId);
Console.WriteLine("Exception: {0}\n{1}",
e.TerminationException.GetType().FullName,
e.TerminationException.Message);
}
else if (e.CompletionState == ActivityInstanceState.Canceled)
{
Console.WriteLine("Workflow {0} Canceled.", e.InstanceId);
}
else
{
Console.WriteLine("Workflow {0} Completed.", e.InstanceId);
// Outputs can be retrieved from the Outputs dictionary,
// keyed by argument name.
// Console.WriteLine("The winner is {0}.", e.Outputs["Winner"]);
}
};
wfApp.Aborted = delegate (WorkflowApplicationAbortedEventArgs e)
{
// Display the exception that caused the workflow
// to abort.
Console.WriteLine("Workflow {0} Aborted.", e.InstanceId);
Console.WriteLine("Exception: {0}\n{1}",
e.Reason.GetType().FullName,
e.Reason.Message);
};
wfApp.Idle = delegate (WorkflowApplicationIdleEventArgs e)
{
// Perform any processing that should occur
// when a workflow goes idle. If the workflow can persist,
// both Idle and PersistableIdle are called in that order.
Console.WriteLine("Workflow {0} Idle.", e.InstanceId);
};
wfApp.PersistableIdle = delegate (WorkflowApplicationIdleEventArgs e)
{
// Instruct the runtime to persist and unload the workflow.
// Choices are None, Persist, and Unload.
return PersistableIdleAction.Unload;
};
wfApp.Unloaded = delegate (WorkflowApplicationEventArgs e)
{
Console.WriteLine("Workflow {0} Unloaded.", e.InstanceId);
};
wfApp.OnUnhandledException = delegate (WorkflowApplicationUnhandledExceptionEventArgs e)
{
// Display the unhandled exception.
Console.WriteLine("OnUnhandledException in Workflow {0}\n{1}",
e.InstanceId, e.UnhandledException.Message);
Console.WriteLine("ExceptionSource: {0} - {1}",
e.ExceptionSource.DisplayName, e.ExceptionSourceInstanceId);
// Instruct the runtime to terminate the workflow.
// Other choices are Abort and Cancel. Terminate
// is the default if no OnUnhandledException handler
// is present.
return UnhandledExceptionAction.Terminate;
};
Setting Input Arguments of a Workflow
Data can be passed into a workflow as it is started using a dictionary of parameters, similar to the way data is passed in when using WorkflowInvoker. Each item in the dictionary maps to an input argument of the specified workflow. In this example, a workflow that consists of a WriteLine activity is invoked and its Text argument is specified using the dictionary of input parameters.
AutoResetEvent syncEvent = new AutoResetEvent(false);
Activity wf = new WriteLine();
// Create the dictionary of input parameters.
Dictionary<string, object> inputs = new Dictionary<string, object>();
inputs.Add("Text", "Hello World!");
// Create the WorkflowApplication using the desired
// workflow definition and dictionary of input parameters.
WorkflowApplication wfApp = new WorkflowApplication(wf, inputs);
// Handle the desired lifecycle events.
wfApp.Completed = delegate (WorkflowApplicationCompletedEventArgs e)
{
syncEvent.Set();
};
// Start the workflow.
wfApp.Run();
// Wait for Completed to arrive and signal that
// the workflow is complete.
syncEvent.WaitOne();
Retrieving Output Arguments of a Workflow
When a workflow completes, any output arguments can be retrieved in the Completed handler by accessing the WorkflowApplicationCompletedEventArgs.Outputs dictionary. The following example hosts a workflow using WorkflowApplication. A WorkflowApplication instance is constructed using a workflow definition consisting of a single DiceRoll activity. The DiceRoll activity has two output arguments that represent the results of the dice roll operation. When the workflow completes, the outputs are retrieved in the Completed handler.
public sealed class DiceRoll : CodeActivity
{
public OutArgument<int> D1 { get; set; }
public OutArgument<int> D2 { get; set; }
static Random r = new Random();
protected override void Execute(CodeActivityContext context)
{
D1.Set(context, r.Next(1, 7));
D2.Set(context, r.Next(1, 7));
}
}
// Create a WorkflowApplication instance.
WorkflowApplication wfApp = new WorkflowApplication(new DiceRoll());
// Subscribe to any desired workflow lifecycle events.
wfApp.Completed = delegate (WorkflowApplicationCompletedEventArgs e)
{
if (e.CompletionState == ActivityInstanceState.Faulted)
{
Console.WriteLine("Workflow {0} Terminated.", e.InstanceId);
Console.WriteLine("Exception: {0}\n{1}",
e.TerminationException.GetType().FullName,
e.TerminationException.Message);
}
else if (e.CompletionState == ActivityInstanceState.Canceled)
{
Console.WriteLine("Workflow {0} Canceled.", e.InstanceId);
}
else
{
Console.WriteLine("Workflow {0} Completed.", e.InstanceId);
// Outputs can be retrieved from the Outputs dictionary,
// keyed by argument name.
Console.WriteLine("The two dice are {0} and {1}.",
e.Outputs["D1"], e.Outputs["D2"]);
}
};
// Run the workflow.
wfApp.Run();
Note
WorkflowApplication and WorkflowInvoker take a dictionary of input arguments and return a dictionary of out arguments. These dictionary parameters, properties, and return values are of type IDictionary<string, object>. The actual instance of the dictionary class that is passed in can be any class that implements IDictionary<string, object>. In these examples, Dictionary<string, object> is used. For more information about dictionaries, see IDictionary<TKey,TValue> and Dictionary<TKey,TValue>.
Passing Data into a Running Workflow Using Bookmarks
Bookmarks are the mechanism by which an activity can passively wait to be resumed and are a mechanism for passing data into a running workflow instance. If an activity is waiting for data, it can create a Bookmark and register a callback method to be called when the Bookmark is resumed, as shown in the following example.
public sealed class ReadLine : NativeActivity<string>
{
[RequiredArgument]
public InArgument<string> BookmarkName { get; set; }
protected override void Execute(NativeActivityContext context)
{
// Create a Bookmark and wait for it to be resumed.
context.CreateBookmark(BookmarkName.Get(context),
new BookmarkCallback(OnResumeBookmark));
}
// NativeActivity derived activities that do asynchronous operations by calling
// one of the CreateBookmark overloads defined on System.Activities.NativeActivityContext
// must override the CanInduceIdle property and return true.
protected override bool CanInduceIdle
{
get { return true; }
}
public void OnResumeBookmark(NativeActivityContext context, Bookmark bookmark, object obj)
{
// When the Bookmark is resumed, assign its value to
// the Result argument.
Result.Set(context, (string)obj);
}
When executed, the ReadLine activity creates a Bookmark, registers a callback, and then waits for the Bookmark to be resumed. When it is resumed, the ReadLine activity assigns the data that was passed with the Bookmark to its Result argument. In this example, a workflow is created that uses the ReadLine activity to gather the user’s name and display it to the console window.
Variable<string> name = new Variable<string>();
Activity wf = new Sequence
{
Variables = { name },
Activities =
{
new WriteLine
{
Text = "What is your name?"
},
new ReadLine
{
BookmarkName = "UserName",
Result = new OutArgument<string>(name)
},
new WriteLine
{
Text = new InArgument<string>((env) =>
("Hello, " + name.Get(env)))
}
}
};
// Create a WorkflowApplication instance.
WorkflowApplication wfApp = new WorkflowApplication(wf);
// Workflow lifecycle events omitted except idle.
AutoResetEvent idleEvent = new AutoResetEvent(false);
wfApp.Idle = delegate (WorkflowApplicationIdleEventArgs e)
{
idleEvent.Set();
};
// Run the workflow.
wfApp.Run();
// Wait for the workflow to go idle before gathering
// the user's input.
idleEvent.WaitOne();
// Gather the user's input and resume the bookmark.
// Bookmark resumption only occurs when the workflow
// is idle. If a call to ResumeBookmark is made and the workflow
// is not idle, ResumeBookmark blocks until the workflow becomes
// idle before resuming the bookmark.
BookmarkResumptionResult result = wfApp.ResumeBookmark("UserName",
Console.ReadLine());
// Possible BookmarkResumptionResult values:
// Success, NotFound, or NotReady
Console.WriteLine("BookmarkResumptionResult: {0}", result);
When the ReadLine activity is executed, it creates a Bookmark named UserName and then waits for the bookmark to be resumed. The host collects the desired data and then resumes the Bookmark. The workflow resumes, displays the name, and then completes.
The host application can inspect the workflow to determine if there are any active bookmarks. It can do this by calling the GetBookmarks method of a WorkflowApplication instance, or by inspecting the WorkflowApplicationIdleEventArgs in the Idle handler.
The following code example is like the previous example except that the active bookmarks are enumerated before the bookmark is resumed. The workflow is started, and once the Bookmark is created and the workflow goes idle, GetBookmarks is called. When the workflow is completed, the following output is displayed to the console.
What is your name?
BookmarkName: UserName - OwnerDisplayName: ReadLine
Steve
Hello, Steve
Variable<string> name = new Variable<string>();
Activity wf = new Sequence
{
Variables = { name },
Activities =
{
new WriteLine
{
Text = "What is your name?"
},
new ReadLine
{
BookmarkName = "UserName",
Result = new OutArgument<string>(name)
},
new WriteLine
{
Text = new InArgument<string>((env) =>
("Hello, " + name.Get(env)))
}
}
};
// Create a WorkflowApplication instance.
WorkflowApplication wfApp = new WorkflowApplication(wf);
// Workflow lifecycle events omitted except idle.
AutoResetEvent idleEvent = new AutoResetEvent(false);
wfApp.Idle = delegate (WorkflowApplicationIdleEventArgs e)
{
// You can also inspect the bookmarks from the Idle handler
// using e.Bookmarks
idleEvent.Set();
};
// Run the workflow.
wfApp.Run();
// Wait for the workflow to go idle and give it a chance
// to create the Bookmark.
idleEvent.WaitOne();
// Inspect the bookmarks
foreach (BookmarkInfo info in wfApp.GetBookmarks())
{
Console.WriteLine("BookmarkName: {0} - OwnerDisplayName: {1}",
info.BookmarkName, info.OwnerDisplayName);
}
// Gather the user's input and resume the bookmark.
wfApp.ResumeBookmark("UserName", Console.ReadLine());
The following code example inspects the WorkflowApplicationIdleEventArgs passed into the Idle handler of a WorkflowApplication instance. In this example the workflow going idle has one Bookmark with a name of EnterGuess, owned by an activity named ReadInt. This code example is based off of How to: Run a Workflow, which is part of the Getting Started Tutorial. If the Idle handler in that step is modified to contain the code from this example, the following output is displayed.
BookmarkName: EnterGuess - OwnerDisplayName: ReadInt
wfApp.Idle = delegate (WorkflowApplicationIdleEventArgs e)
{
foreach (BookmarkInfo info in e.Bookmarks)
{
Console.WriteLine("BookmarkName: {0} - OwnerDisplayName: {1}",
info.BookmarkName, info.OwnerDisplayName);
}
idleEvent.Set();
};
Summary
WorkflowInvoker provides a lightweight way to invoke workflows, and although it provides methods for passing data in at the start of a workflow and extracting data from a completed workflow, it does not provide for more complex scenarios which is where WorkflowApplication can be used.
