How to: Create an Activity

Article
07/29/2022

Activities are the core unit of behavior in WF. The execution logic of an activity can be implemented in managed code or it can be implemented by using other activities. This topic demonstrates how to create two activities. The first activity is a simple activity that uses code to implement its execution logic. The implementation of the second activity is defined by using other activities. These activities are used in following steps in the tutorial.

Create the activity library project

Open Visual Studio and choose New > Project from the File menu.
In the New Project dialog, under the Installed category, select Visual C# > Workflow (or Visual Basic > Workflow).

Note

If you don't see the Workflow template category, you may need to install the Windows Workflow Foundation component of Visual Studio. Choose the Open Visual Studio Installer link on the left-hand side of the New Project dialog. In Visual Studio Installer, select the Individual components tab. Then, under the Development activities category, select the Windows Workflow Foundation component. Choose Modify to install the component.
Select the Activity Library project template. Type NumberGuessWorkflowActivities in the Name box and then click OK.
Right-click Activity1.xaml in Solution Explorer and choose Delete. Click OK to confirm.

Create the ReadInt activity

Choose Add New Item from the Project menu.
In the Installed > Common Items node, select Workflow. Select Code Activity from the Workflow list.
Type ReadInt into the Name box and then click Add.

Replace the existing ReadInt definition with the following definition.

public sealed class ReadInt : NativeActivity<int>
{
    [RequiredArgument]
    public InArgument<string> BookmarkName { get; set; }

    protected override void Execute(NativeActivityContext context)
    {
        string name = BookmarkName.Get(context);

        if (string.IsNullOrEmpty(name))
        {
            throw new ArgumentException("BookmarkName cannot be an Empty string.",
                "context");
        }

        context.CreateBookmark(name, new BookmarkCallback(OnReadComplete));
    }

    // 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; }
    }

    void OnReadComplete(NativeActivityContext context, Bookmark bookmark, object state)
    {
        this.Result.Set(context, Convert.ToInt32(state));
    }
}

Public NotInheritable Class ReadInt
    Inherits NativeActivity(Of Integer)

    <RequiredArgument()>
    Property BookmarkName() As InArgument(Of String)

    Protected Overrides Sub Execute(ByVal context As NativeActivityContext)
        Dim name As String
        name = BookmarkName.Get(context)

        If name = String.Empty Then
            Throw New ArgumentException("BookmarkName cannot be an Empty string.",
                "BookmarkName")
        End If

        context.CreateBookmark(name, New BookmarkCallback(AddressOf OnReadComplete))
    End Sub

    ' 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 Overrides ReadOnly Property CanInduceIdle As Boolean
        Get
            Return True
        End Get
    End Property

    Sub OnReadComplete(ByVal context As NativeActivityContext, ByVal bookmark As Bookmark, ByVal state As Object)
        Result.Set(context, Convert.ToInt32(state))
    End Sub

End Class

Note

The ReadInt activity derives from NativeActivity<TResult> instead of CodeActivity, which is the default for the code activity template. CodeActivity<TResult> can be used if the activity provides a single result, which is exposed through the Result argument, but CodeActivity<TResult> does not support the use of bookmarks, so NativeActivity<TResult> is used.

Create the Prompt activity

Press Ctrl+Shift+B to build the project. Building the project enables the ReadInt activity in this project to be used to build the custom activity from this step.
Choose Add New Item from the Project menu.
In the Installed > Common Items node, select Workflow. Select Activity from the Workflow list.
Type Prompt into the Name box and then click Add.
Double-click Prompt.xaml in Solution Explorer to display it in the designer if it is not already displayed.
Click Arguments in the lower-left side of the activity designer to display the Arguments pane.
Click Create Argument.
Type BookmarkName into the Name box, select In from the Direction drop-down list, select String from the Argument type drop-down list, and then press Enter to save the argument.
Click Create Argument.
Type Result into the Name box that is underneath the newly added BookmarkName argument, select Out from the Direction drop-down list, select Int32 from the Argument type drop-down list, and then press Enter.
Click Create Argument.
Type Text into the Name box, select In from the Direction drop-down list, select String from the Argument type drop-down list, and then press Enter to save the argument.

These three arguments are bound to the corresponding arguments of the WriteLine and ReadInt activities that are added to the Prompt activity in the following steps.
Click Arguments in the lower-left side of the activity designer to close the Arguments pane.
Drag a Sequence activity from the Control Flow section of the Toolbox and drop it onto the Drop activity here label of the Prompt activity designer.

Tip

If the Toolbox window is not displayed, select Toolbox from the View menu.
Drag a WriteLine activity from the Primitives section of the Toolbox and drop it onto the Drop activity here label of the Sequence activity.
Bind the Text argument of the WriteLine activity to the Text argument of the Prompt activity by typing Text into the Enter a C# expression or Enter a VB expression box in the Properties window, and then press the Tab key two times. This dismisses the IntelliSense list members window and saves the property value by moving the selection off the property. This property can also be set by typing Text into the Enter a C# expression or Enter a VB expression box on the activity itself.

Tip

If the Properties Window is not displayed, select Properties Window from the View menu.
Drag a ReadInt activity from the NumberGuessWorkflowActivities section of the Toolbox and drop it in the Sequence activity so that it follows the WriteLine activity.
Bind the BookmarkName argument of the ReadInt activity to the BookmarkName argument of the Prompt activity by typing BookmarkName into the Enter a VB expression box to the right of the BookmarkName argument in the Properties Window, and then press the Tab key two times to close the IntelliSense list members window and save the property.
Bind the Result argument of the ReadInt activity to the Result argument of the Prompt activity by typing Result into the Enter a VB expression box to the right of the Result argument in the Properties Window, and then press the Tab key two times.
Press Ctrl+Shift+B to build the solution.

Next steps

For instructions on how to create a workflow by using these activities, see the next step in the tutorial, How to: Create a Workflow.

How to: Create an Activity

Create the activity library project

Create the ReadInt activity

Create the Prompt activity

Next steps

See also

Feedback

Additional resources