在线程之间传递对象会导致异常，因为不同的线程拥有它

Question

我之前遇到过这种问题，通过自定义类引发的事件更新 GUI 元素，但我能够通过以下方式解决它：

MyTextBlock.Dispatcher.BeginInvoke(DispatcherPriority.Normal,
      (Action)(() => { LoggingTextBlock.Text += Message += "\r\n"; }));

我认为这个问题是 UI 线程独有的，但显然它适用于所有线程。不幸的是，我的自定义类没有像 UIElements 那样调用的 .Dispatcher() 例程。那么你应该如何将对象传递给其他线程并让它们能够使用它们呢？

例如，我有一个基础侦听器类，其主要工作基本上是查找一些数据、引发事件并传递该数据。以下是我要传递的数据类的一部分：

// Just the class for carrying the job data.
public class JobData
{
    // NOTE: I don't no have trouble accessing these properties from a 
    // different thread
    public string SomeProperty1 { get; set; }
    public string SomeProperty2 { get; set; }
    public string SomeProperty3 { get; set; }

    // ...
    // more properties
    // ...

    // This a .NET object of type System.Printing.PrintSystemJobInfo.  This
    // is the guy that gives me trouble.  Later on, I can't access members 
    // of Job without getting the "The calling thread cannot access this 
    // object because a different thread owns it" error.
    PrintSystemJobInfo m_Job = null;
    public PrintSystemJobInfo Job
    {
        get
        {
            if (m_Job == null)
            { throw new ArgumentNullException(); }

            return m_Job;
        }

        set { m_Job = value; }
    }
}

以下是类的一部分，它在线程中运行、收集数据并触发事件以将该数据传递给任何收听的人。

// Thread who monitors looking for data to package into JobData and send
// to any listeners.
public class JobMonitor
{
    public delegate void NewJobEvent(JobData jobStuff);
    public event NewJobEvent NewJob;

    // Call this when you have some job data and need to notify listeners
    private void OnNewJob(object newJobData)
    {
        JobData newJobData = (JobData)newJobData;
        if (NewJob != null)
        {
            NewJob(newJobData);
        }
    }

    private void WorkerRoutine()
    {
        while(true)
        {
            // Wait for data

            // ...
            // ...

            // when data is found

            JobData myJobData = new JobData();
            myJobData.SomeProperty1 = "some data";
            myJobData.SomeProperty2 = "some data";

            int jobID = GetCurrentJobID();
            string printerName = GetCurrentPrinterName();

            // .NET class System.Printing.PrintQueue
            PrintQueue printQueue = new PrintQueue(new PrintServer(), printerName);

            PrintSystemJobInfo jobInfo = null;
            jobInfo = printQueue.GetJob(jobID);

            // This is the guy in my JobData class that I'll have trouble accessing
            // later on.
            myJobData.Job = jobInfo;

            // Time to fire off the event
            OnNewJob(myJobData);
        }
    }
}

以下是实例化 JobMonitor 类并捕获其事件的类的一部分。它无法访问 JobMonitor 的属性之一。

// This class signs up to recieve and process events from the JobMonitor class.
public class JobProcessor
{
    // this is the method that handles the incoming job events.  This is where 
    // i have trouble.
    private void NewJobEventHandler(JobData newJob)
    {
        string temp = newJob.SomeProperty1; // this works fine

        bool bTemp = newJob.Job.IsPaused;   // this throws an exception "The
                                            // calling read cannot access this
                                            // object because a different thread
                                            // owns it"
    }

    private JobMonitor m_monitor = null;
    public JobProcessor()
    {
        m_monitor = new JobMonitor();

        //attaches a method to handle incoming job events.
        m_monitor.NewJob += new JobMonitor.NewJobEvent(NewJobEventHandler);
        m_monitor.Start();
    }
}

所以 JobProcessor.NewJobEventHandler() 方法是我得到异常“调用线程无法访问此对象，因为不同的线程拥有它”的地方。我需要能够访问此属性以及下面的属性和方法。我需要做什么才能访问我需要的东西？

Answer 1

我会研究 System.Threading 提供的SyncronizationContext。此类具有静态属性 Current，它将提供您正在寻找的 Dispatcher 样式调用。

其他可能性

如果您想在与创建 JobData 类的线程不同的线程上处理事件，那么您可能需要将 PrintSystemJobInfo 的实际检索移至事件处理程序。

另一种选择是使用您创建的新类（没有线程亲和性）抽象出 System 类。