如何将参数传递给 NativeActivity 代码序列中的 CodeActivity

Question

我正在尝试让 Windows 工作流程正常运行，但我有点困惑。

我已经有了一个工作流程，但现在我正在尝试做一些更复杂的事情：启动一个工作流程，其中每个活动本身都包含一个工作流程。 （想象一下主程序启动“输入、逻辑和输出”活动，然后每个活动都有附加活动，例如“提示用户、获取输入等”）

我已经让它工作正常，例如从这里（http://msdn.microsoft.com/en-us/magazine/gg535667.aspx），当我没有将任何参数从主程序传递到活动时。我的问题是，“Variables”和“metadata.SetVariablesCollection”在 NativeActivity 中到底如何工作，以及如何获取低级别活动的参数？

这就是我当前正在尝试的：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Activities;
using System.Collections.ObjectModel;
using System.Activities.Statements;

namespace Project1
{
    internal class MainProgram
    {
        internal static void Main(string[] args)
        {
            try
            {
                var act = new SimpleSequence();

                act.Activities.Add((Activity)(new WriteSomeText()));
                act.Activities.Add((Activity)(new WriteSomeText()));
                act.Activities.Add((Activity)(new WriteSomeText()));

                act.Variables.Add(new Variable<string> ("stringArg", "TEXT"));

                WorkflowInvoker.Invoke(act);
            }
            catch (Exception ex)
            {
                System.Console.WriteLine("EXCEPTION: {0}", ex);
            }
        }

        public class WriteSomeText : CodeActivity
        {
            [RequiredArgument]
            public InArgument<string> stringArg { get; set; }

            protected override void Execute(CodeActivityContext context)
            {
                string output = context.GetValue(stringArg);
                System.Console.WriteLine(output);
            }

        }

        public class SimpleSequence : NativeActivity
        {
            Collection<Activity> activities;
            Collection<Variable> variables;

            Variable<int> current = new Variable<int> { Default = 0 };

            public Collection<Activity> Activities
            {
                get
                {
                    if (this.activities == null)
                        this.activities = new Collection<Activity>();

                    return this.activities;
                }
                set
                {
                    this.activities = value;
                }
            }

            public Collection<Variable> Variables
            {
                get
                {
                    if (this.variables == null)
                        this.variables = new Collection<Variable>();

                    return this.variables;
                }
                set
                {
                    this.variables = value;
                }
            }

            protected override void CacheMetadata(NativeActivityMetadata metadata)
            {
                metadata.SetChildrenCollection(this.activities);
                metadata.SetVariablesCollection(this.variables);
                metadata.AddImplementationVariable(this.current);
            }

            protected override void Execute(NativeActivityContext context)
            {
                if (this.Activities.Count > 0)
                    context.ScheduleActivity(this.Activities[0], onChildComplete);
            }

            void onChildComplete(NativeActivityContext context, ActivityInstance completed)
            {
                int currentExecutingActivity = this.current.Get(context);
                int next = currentExecutingActivity + 1;

                if (next < this.Activities.Count)
                {
                    context.ScheduleActivity(this.Activities[next], this.onChildComplete);

                    this.current.Set(context, next);
                }
            }
        }
    }
}

这最终会引发以下异常：

EXCEPTION: System.Activities.InvalidWorkflowException: The following errors were encountered while processing the workflow tree:
'WriteSomeText': Value for a required activity argument 'stringArg' was not supplied.
'WriteSomeText': Value for a required activity argument 'stringArg' was not supplied.
'WriteSomeText': Value for a required activity argument 'stringArg' was not supplied.
   at System.Activities.Validation.ActivityValidationServices.ThrowIfViolationsExist(IList`1 validationErrors)
   at System.Activities.Hosting.WorkflowInstance.ValidateWorkflow(WorkflowInstanceExtensionManager extensionManager)
   at System.Activities.Hosting.WorkflowInstance.RegisterExtensionManager(WorkflowInstanceExtensionManager extensionManager)
   at System.Activities.WorkflowApplication.EnsureInitialized()
   at System.Activities.WorkflowApplication.RunInstance(WorkflowApplication instance)
   at System.Activities.WorkflowApplication.Invoke(Activity activity, IDictionary`2 inputs, WorkflowInstanceExtensionManager extensions, TimeSpan timeout)
   at System.Activities.WorkflowInvoker.Invoke(Activity workflow, TimeSpan timeout, WorkflowInstanceExtensionManager extensions)
   at System.Activities.WorkflowInvoker.Invoke(Activity workflow)
   at Project1.MainProgram.Main(String[] args) in c:\users\user\documents\visual studio 2010\Projects\ModelingProject1\Project1\MainProgram.cs:line 25

我知道，我只传递了 1 个参数，但异常仍然表明我缺少 3 个参数。我缺少一些关于如何正确执行此操作的信息。

Answer 1

您正确地将stringArg声明为InArgument，但在SimpleSequence内部调用它时没有向它传递任何值。

您可以使用构造函数传递一些内容，同时构造所有活动本身，如下所示：

public class WriteSomeText : CodeActivity
{
    [RequiredArgument]
    public InArgument<string> stringArg { get; set; }

    public WriteSomeText(string stringArg)
    {
        this.stringArg = stringArg;
    }

    protected override void Execute(CodeActivityContext context
    {
        string output = context.GetValue(stringArg);
        System.Console.WriteLine(output);
    }
}

// Calling the activity like this:

internal static void Main(string[] args)
{
    var act = new SimpleSequence()
    {
        Activities =
        {
            new WriteSomeText("hello"),
            new WriteSomeText("world"),
            new WriteSomeText("!")
        }
    };

    WorkflowInvoker.Invoke(act);

    Console.WriteLine("Press any key to exit");
    Console.ReadKey();
}

另请注意，这是使用构造函数初始化集合的最佳实践：

public SimpleSequence()
{
    activities = new Collection<Activity>();
    variables = new Collection<Variable>();
}

这种方式初始化活动更加直观：

var act = new SimpleSequence()
{
    Activities =
    {
        new WriteSomeText("hello"),
        new WriteSomeText("world"),
        new WriteSomeText("!")
    },
    Variables =
    {
        new Variable<int>("myNewIntVar", 10),
        // ....
    }
};

编辑：

有几个解决问题的其他方法。 这是您刚进入 WF4 世界时最好的朋友。

检查WF\Basic\CustomActivities\Code-Bodied以获取有关此特殊情况的一些推动。