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書名： Microsoft Windows Workflow Foundation 4.0 Cookbook
作者名： Andrew Zhu
本章字?jǐn)?shù)： 331字
更新時(shí)間： 2021-04-13 17:00:35

Creating a WF program using OutArgument

In this task, we will create a WF program that can return a result to the workflow host.

How to do it...

Create a workflow project:
Create a new Workflow Console Application under the Chapter01 solution; name the project as UseOutArgument.
Author a workflow:
Author the workflow shown in the following screenshot. Here are the detailed actions:
1. Drag a Sequence activity from Toolbox to the designer panel.
2. In the bottom of the designer panel, click the Arguments button, and click Create Argument to create an OutArgument string named OutMessage.
3. Drag two WriteLine activities from Toolbox into the Sequence activity and fill the textboxes with "Start…" and "End" respectively.
4. Drag an Assign activity from Toolbox to the designer panel. Fill the right expression box with OutArgument as OutMessage, whereas fill the right expression box with the following string: This is a message from workflow.

Write code to host the workflow:

Open Program.cs file and change the host code as follows:

using System;
using System.Activities;
using System.Collections.Generic;

namespace UseOutArgument {
    class Program {
        static void Main(string[] args) {
            IDictionary<string,object> output=
                WorkflowInvoker.Invoke(new Workflow1());
            Console.WriteLine(output["OutMessage"]);
        }
    }
}

Run it:
Set UseOutArgument as Startup project. Press Ctrl+F5 to build and run the workflow without debugging. The application should run in a console window and print the message as shown in the next screenshot:

How it works...

Look at the following code snippet:

IDictionary<string,object> output=
     WorkflowInvoker.Invoke(new Workflow1());
Console.WriteLine(output["OutMessage"]);

OutMessage is the name of OutArgument we defined in Workflow1.xaml. the WorkflowInvoder.Invoke method will return a IDictionary type object.

There's more...

There is a third type of workflow argument: InOutArgument. It is a binding terminal that represents the flow of data into and out of an activity. In most cases, we can use InOutArgument instead of InArgument and OutArgument. But there are still some differences—for example, we cannot assign a string to InOutArgument, while it is allowed to assign a string to InArgument directly in the host program.

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Microsoft Windows Workflow Foundation 4.0 Cookbook