WF4：使用SymbolResolver 在自定义活动中访问外部宿主信息[译]

 先看看System.Activities.Hosting.SymbolResolver 的定义：

public sealed class SymbolResolver : IDictionary<string, Object>, 
    ICollection<KeyValuePair<string, Object>>, IEnumerable<KeyValuePair<string, Object>>, 
    IEnumerable

 实现了IDictionary<string, Object> 接口，我们在工作流宿主中将需要在自定义Activity中访问的变量加入到SymbolResolver 中，然后在Activity中获取

SymbolResolver 实例，再通过key访问需要的变量，代码如下：

  

//定义信息包装类：
public class MyObject
{
  public int MyValue { get; set; }
  public string MyString { get; set; }
}

//将SymbolResolver作为Extension加入到WorkflowApplication中
class Program
{
  static void Main(string[] args)
  {
    WorkflowApplication WFApp = new WorkflowApplication(new Workflow1());
    SymbolResolver symbolResolver = new SymbolResolver();
    WFApp.Extensions.Add(symbolResolver);
    symbolResolver.Add("CustomObject", new SymbolUserActivity.MyObject() { MyValue = 1, MyString = "TestString" });
    WFApp.Run();
    Console.ReadLine();
  }
}

//在自定义活动中访问MyObject实例
public sealed class SymbolUser : CodeActivity
{
  protected override void Execute(CodeActivityContext context)
  {
    SymbolResolver symbolResolver = context.GetExtension<SymbolResolver>();
    MyObject obj = symbolResolver["CustomObject"] as MyObject;
    Console.WriteLine(obj.MyString);
  }
}

最后要注意的是： SymbolResolver 不会参与工作流持久化过程。

原文：Using a WF4 SymbolResolver to access host environment information