How to: Run a Workflow

.NET Framework (current version)
 

This topic is a continuation of the Windows Workflow Foundation Getting Started tutorial and discusses how to create a workflow host and run the workflow defined in the previous How to: Create a Workflow topic.

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Each topic in the Getting Started tutorial depends on the previous topics. To complete this topic you must first complete How to: Create an Activity and How to: Create a Workflow.

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To download a completed version of the tutorial, see Windows Workflow Foundation (WF45) - Getting Started Tutorial.

To create the workflow host project

  1. Open the solution from the previous How to: Create an Activity topic by using Visual Studio 2012.

  2. Right-click the WF45GettingStartedTutorial solution in Solution Explorer and select Add, New Project.

    System_CAPS_tipTip

    If the Solution Explorer window is not displayed, select Solution Explorer from the View menu.

  3. In the Installed node, select Visual C#, Workflow (or Visual Basic, Workflow).

    System_CAPS_noteNote

    Depending on which programming language is configured as the primary language in Visual Studio, the Visual C# or Visual Basic node may be under the Other Languages node in the Installed node.

    Ensure that .NET Framework 4.5 is selected in the .NET Framework version drop-down list. Select Workflow Console Application from the Workflow list. Type NumberGuessWorkflowHost into the Name box and click OK. This creates a starter workflow application with basic workflow hosting support. This basic hosting code is modified and used to run the workflow application.

  4. Right-click the newly added NumberGuessWorkflowHost project in Solution Explorer and select Add Reference. Select Solution from the Add Reference list, check the checkbox beside NumberGuessWorkflowActivities, and then click OK.

  5. Right-click Workflow1.xaml in Solution Explorer and choose Delete. Click OK to confirm.

To modify the workflow hosting code

  1. Double-click Program.cs or Module1.vb in Solution Explorer to display the code.

    System_CAPS_tipTip

    If the Solution Explorer window is not displayed, select Solution Explorer from the View menu.

    Because this project was created by using the Workflow Console Application template, Program.cs or Module1.vb contains the following basic workflow hosting code.

    // Create and cache the workflow definition
    Activity workflow1 = new Workflow1();
    WorkflowInvoker.Invoke(workflow1);
    

    This generated hosting code uses WorkflowInvoker. 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 life-cycle events, execution control, bookmark resumption, and persistence. This example uses bookmarks and WorkflowApplication is used for hosting the workflow. Add the following using or Imports statement at the top of Program.cs or Module1.vb below the existing using or Imports statements.

    using NumberGuessWorkflowActivities;
    using System.Threading;
    

    Replace the lines of code that use WorkflowInvoker with the following basic WorkflowApplication hosting code. This sample hosting code demonstrates the basic steps for hosting and invoking a workflow, but does not yet contain the functionality to successfully run the workflow from this topic. In the following steps, this basic code is modified and additional features are added until the application is complete.

    System_CAPS_noteNote

    Please replace Workflow1 in these examples with FlowchartNumberGuessWorkflow, SequentialNumberGuessWorkflow, or StateMachineNumberGuessWorkflow, depending on which workflow you completed in the previous How to: Create a Workflow step. If you do not replace Workflow1 then you will get build errors when you try and build or run the workflow.

    AutoResetEvent syncEvent = new AutoResetEvent(false);
    
    WorkflowApplication wfApp =
        new WorkflowApplication(new Workflow1());
    
    wfApp.Completed = delegate(WorkflowApplicationCompletedEventArgs e)
    {
        syncEvent.Set();
    };
    
    wfApp.Aborted = delegate(WorkflowApplicationAbortedEventArgs e)
    {
        Console.WriteLine(e.Reason);
        syncEvent.Set();
    };
    
    wfApp.OnUnhandledException = delegate(WorkflowApplicationUnhandledExceptionEventArgs e)
    {
        Console.WriteLine(e.UnhandledException.ToString());
        return UnhandledExceptionAction.Terminate;
    };
    
    wfApp.Run();
    
    syncEvent.WaitOne();
    

    This code creates a WorkflowApplication, subscribes to three workflow life-cycle events, starts the workflow with a call to Run, and then waits for the workflow to complete. When the workflow completes, the AutoResetEvent is set and the host application completes.

To set input arguments of a workflow

  1. Add the following statement at the top of Program.cs or Module1.vb below the existing using or Imports statements.

    using System.Collections.Generic;
    
  2. Replace the line of code that creates the new WorkflowApplication with the following code that creates and passes a dictionary of parameters to the workflow when it is created.

    System_CAPS_noteNote

    Please replace Workflow1 in these examples with FlowchartNumberGuessWorkflow, SequentialNumberGuessWorkflow, or StateMachineNumberGuessWorkflow, depending on which workflow you completed in the previous How to: Create a Workflow step. If you do not replace Workflow1 then you will get build errors when you try and build or run the workflow.

    var inputs = new Dictionary<string, object>() { { "MaxNumber", 100 } };
    
    WorkflowApplication wfApp =
        new WorkflowApplication(new Workflow1(), inputs);
    

    This dictionary contains one element with a key of MaxNumber. Keys in the input dictionary correspond to input arguments on the root activity of the workflow. MaxNumber is used by the workflow to determine the upper bound for the randomly generated number.

To retrieve output arguments of a workflow

  1. Modify the Completed handler to retrieve and display the number of turns used by the workflow.

    wfApp.Completed = delegate(WorkflowApplicationCompletedEventArgs e)
    {
        int Turns = Convert.ToInt32(e.Outputs["Turns"]);
        Console.WriteLine("Congratulations, you guessed the number in {0} turns.", Turns);
    
        syncEvent.Set();
    };
    

To resume a bookmark

  1. Add the following code at the top of the Main method just after the existing AutoResetEvent declaration.

    AutoResetEvent idleEvent = new AutoResetEvent(false);
    
  2. Add the following Idle handler just below the existing three workflow life-cycle handlers in Main.

    wfApp.Idle = delegate(WorkflowApplicationIdleEventArgs e)
    {
        idleEvent.Set();
    };
    

    Each time the workflow becomes idle waiting for the next guess, this handler is called and the idleAction AutoResetEvent is set. The code in the following step uses idleEvent and syncEvent to determine whether the workflow is waiting for the next guess or is complete.

    System_CAPS_noteNote

    In this example, the host application uses auto-reset events in the Completed and Idle handlers to synchronize the host application with the progress of the workflow. It is not necessary to block and wait for the workflow to become idle before resuming a bookmark, but in this example the synchronization events are required so the host knows whether the workflow is complete or whether it is waiting on more user input by using the Bookmark. For more information, see Bookmarks.

  3. Remove the call to WaitOne, and replace it with code to gather input from the user and resume the Bookmark.

    Remove the following line of code.

    syncEvent.WaitOne();
    

    Replace it with the following example.

    // Loop until the workflow completes.
    WaitHandle[] handles = new WaitHandle[] { syncEvent, idleEvent };
    while (WaitHandle.WaitAny(handles) != 0)
    {
        // Gather the user input and resume the bookmark.
        bool validEntry = false;
        while (!validEntry)
        {
            int Guess;
            if (!Int32.TryParse(Console.ReadLine(), out Guess))
            {
                Console.WriteLine("Please enter an integer.");
            }
            else
            {
                validEntry = true;
                wfApp.ResumeBookmark("EnterGuess", Guess);
            }
        }
    }
    

To build and run the application

  1. Right-click NumberGuessWorkflowHost in Solution Explorer and select Set as StartUp Project.

  2. Press CTRL+F5 to build and run the application. Try to guess the number in as few turns as possible.

    To try the application with one of the other styles of workflow, replace Workflow1 in the code that creates the WorkflowApplication with FlowchartNumberGuessWorkflow, SequentialNumberGuessWorkflow, or StateMachineNumberGuessWorkflow, depending on which workflow style you desire.

    var inputs = new Dictionary<string, object>() { { "MaxNumber", 100 } };
    
    WorkflowApplication wfApp =
        new WorkflowApplication(new Workflow1(), inputs);
    

    For instructions about how to add persistence to a workflow application, see the next topic, How to: Create and Run a Long Running Workflow.

Example

The following example is the complete code listing for the Main method.

System_CAPS_noteNote

Please replace Workflow1 in these examples with FlowchartNumberGuessWorkflow, SequentialNumberGuessWorkflow, or StateMachineNumberGuessWorkflow, depending on which workflow you completed in the previous How to: Create a Workflow step. If you do not replace Workflow1 then you will get build errors when you try and build or run the workflow.

static void Main(string[] args)
{
    AutoResetEvent syncEvent = new AutoResetEvent(false);
    AutoResetEvent idleEvent = new AutoResetEvent(false);

    var inputs = new Dictionary<string, object>() { { "MaxNumber", 100 } };

    WorkflowApplication wfApp =
        new WorkflowApplication(new Workflow1(), inputs);

    wfApp.Completed = delegate(WorkflowApplicationCompletedEventArgs e)
    {
        int Turns = Convert.ToInt32(e.Outputs["Turns"]);
        Console.WriteLine("Congratulations, you guessed the number in {0} turns.", Turns);

        syncEvent.Set();
    };

    wfApp.Aborted = delegate(WorkflowApplicationAbortedEventArgs e)
    {
        Console.WriteLine(e.Reason);
        syncEvent.Set();
    };

    wfApp.OnUnhandledException = delegate(WorkflowApplicationUnhandledExceptionEventArgs e)
    {
        Console.WriteLine(e.UnhandledException.ToString());
        return UnhandledExceptionAction.Terminate;
    };

    wfApp.Idle = delegate(WorkflowApplicationIdleEventArgs e)
    {
        idleEvent.Set();
    };

    wfApp.Run();

    // Loop until the workflow completes.
    WaitHandle[] handles = new WaitHandle[] { syncEvent, idleEvent };
    while (WaitHandle.WaitAny(handles) != 0)
    {
        // Gather the user input and resume the bookmark.
        bool validEntry = false;
        while (!validEntry)
        {
            int Guess;
            if (!Int32.TryParse(Console.ReadLine(), out Guess))
            {
                Console.WriteLine("Please enter an integer.");
            }
            else
            {
                validEntry = true;
                wfApp.ResumeBookmark("EnterGuess", Guess);
            }
        }
    }
}
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