c# - Workflow Foundation 中自定义事件所需参数的默认值

Question

在为重新托管的工作流程设计器编写自定义事件时，它会给我一个错误，如果我没有所需参数，则需要一个值，因此我要么使用如下所示的 null ，要么使用“ALL ”。它不接受 null 或“ALL”或任何其他内容作为默认参数。请注意，我所需的参数是字符串类型。

[RequiredArgument]
[DefaultValue(null)]
[Description(@"The status of the job to perform")]
public InArgument<string> JobStatus { get; set; }

[RequiredArgument]
[DefaultValue("All")]
[Description(@"The status of the job to perform")]
public InArgument<string> JobStatus { get; set; }

运行工作流程时出现错误消息:

Workflow Console: Starting Workflow...

Could not start workflow.

Message: Failed to start workflow DynamicActivity.

Exception message: The following errors were encountered while processing the workflow tree: 'DynamicActivity': The private implementation of activity '1: DynamicActivity' has the following validation error: Value for a required activity argument 'JobStatus' was not supplied.

Stack trace: 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.Enqueue(InstanceOperation operation, Boolean push) at System.Activities.WorkflowApplication.WaitForTurn(InstanceOperation operation, TimeSpan timeout) at System.Activities.WorkflowApplication.InternalRun(TimeSpan timeout, Boolean isUserRun) at System.Activities.WorkflowApplication.Run()

感谢您的帮助

Answer 1

工作流运行时和工作流设计器都不会查看DefaultValueAttribute。搜索属性需要反射，这可能会降低性能。此外，这不是该属性的目的。

无论如何，您可以使用默认值初始化变量。在构造函数上，例如:

public class MyCodeActivity : CodeActivity
{
    public MyCodeActivity()
    {
        JobStatus = "All";
    }
}

或通过访问器强制指定一个值。像这样的事情:

private InArgument<string> text = "All";

[RequiredArgument]
public InArgument<string> Text
{
    get { return text ?? "All"; }
    set { text = value; }
}

这些是不同的方法，请使用适合您想要的行为的方法。在这两种情况下，始终可以通过 XAML 修改该值，因此对运行时进行少量检查可能会更好:

protected override void Execute(CodeActivityContext context)
{
    string text = context.GetValue(this.Text);
    if (text == null) 
    {
        text = "All";
    }

    Console.WriteLine(text);
}