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書名： Microsoft Windows Workflow Foundation 4.0 Cookbook
作者名： Andrew Zhu
本章字數： 311字
更新時間： 2021-04-13 17:00:36

Converting a WF program instance to XAML

In real applications, we would like to write and test WF programs in imperative code, while storing, running, and transmitting workflow as an XAML string or file. In this task, we will convert a WF program instance to an XAML string.

How to do it...

Create a workflow project:
Create a new Workflow Console Application under the Chapter01 solution and name the project ConvertWFInstanceToXML. Delete the Workflow1.xaml file that is created by default.

Write code to create the workflow and its host:

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

using System;
using System.Activities;
using System.Activities.Statements;
using System.Text;
using System.Xaml;
using System.Activities.XamlIntegration;
using System.IO;

namespace ConvertWFObjectToXML {
    class Program {
        static void Main(string[] args) {
            //Create a Workflow instance object
            ActivityBuilder ab = new ActivityBuilder();
            ab.Implementation = new Sequence() 
            {
                Activities =
                {
                    new WriteLine{Text="Message from Workflow"}
                }
            };

            //Convert Workflow instance to xml string
            StringBuilder sb = new StringBuilder();
            StringWriter sw = new StringWriter(sb);
            XamlWriter xw = 
                ActivityXamlServices.CreateBuilderWriter(
                new XamlXmlWriter(sw, 
                                  new XamlSchemaContext()));
            XamlServices.Save(xw, ab);
            Console.WriteLine(sb.ToString());
        }
    }
}

Run it:
Set ConvertWFInstanceToXML 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 following screenshot:

Consider the following XML string reformatted from the screenshot:

<?xml version="1.0" encoding="utf-16"?>
<Activity  x:Class="{x:Null}" 
                  xmlns="http://schemas.microsoft.com/netfx/2009/xaml/activities" 
                  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
       <Sequence>
            <WriteLine Text="Hello" />
       </Sequence>
</Activity>

How it works...

Consider the following code line:

XamlServices.Save(xw, ab);

XamlServices provides services for the common XAML tasks of reading XAML and writing an object graph, or reading an object and writing out an XAML file. This statement reads an ActivityBuilder object and writes XAML to an XamlWriter object.

We use ActivityBuilder as an activity wrapper so that the output XAML is a loadable workflow. In other words, if we save, say, a Sequence activity to an XamlWriter directly, then the output XML workflow will be unloadable for further use.

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Microsoft Windows Workflow Foundation 4.0 Cookbook