Question

以下是我正在尝试使用我的应用程序完成的任务 - 当HTML文件添加到目录时（使用FileSystemWatcher），我想立即使用WebBrowser打印它。除非我遇到以下错误：

System.Threading.ThreadStateException: ActiveX control GUID cannot be instantiated because the current thread is not in a single-threaded apartment

以下是我正在使用的代码遇到此问题。（我在Main（）之前有[STAThread]）

public Form1()
    {
        InitializeComponent();
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        //  Create a FileSystemWatcher to monitor all files on drive C.
        FileSystemWatcher fsw = new FileSystemWatcher("C:\\Test");

        //  Watch for changes in LastAccess and LastWrite times, and 
        //  the renaming of files or directories. 
        fsw.NotifyFilter = NotifyFilters.LastAccess | NotifyFilters.LastWrite
            | NotifyFilters.FileName | NotifyFilters.DirectoryName;

        //  Register a handler that gets called when a  
        //  file is created, changed, or deleted.
        //fsw.Changed += new FileSystemEventHandler(OnChanged);

        fsw.Created += new FileSystemEventHandler(OnChanged);

        //fsw.Deleted += new FileSystemEventHandler(OnChanged);
        fsw.EnableRaisingEvents = true;

        PrinterSettings settings = new PrinterSettings();
        label2.Text = settings.PrinterName;

        Thread.CurrentThread.SetApartmentState(ApartmentState.STA);
    }

    private void OnChanged(object source, FileSystemEventArgs e)
    {
        notifyIcon1.BalloonTipText = "Printing document " + e.Name + "...";
        notifyIcon1.BalloonTipTitle = "Printing Application";
        notifyIcon1.BalloonTipIcon = ToolTipIcon.Info;
        notifyIcon1.ShowBalloonTip(500);

        PrintCOAPage(e.Name);
    }

    private void PrintCOAPage(string name)
    {
        try
        {
            // Create a WebBrowser instance. 
            WebBrowser webBrowserForPrinting = new WebBrowser();

            // Add an event handler that prints the document after it loads.
            webBrowserForPrinting.DocumentCompleted +=
                new WebBrowserDocumentCompletedEventHandler(PrintDocument);

            // Set the Url property to load the document.
            webBrowserForPrinting.Url = new Uri(@"C:\\Test\\" + name);
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.ToString());
        }
    }

    private void PrintDocument(object sender,
        WebBrowserDocumentCompletedEventArgs e)
    {
        try
        {
            // Print the document now that it is fully loaded.
            ((WebBrowser)sender).Print();

            // Dispose the WebBrowser now that the task is complete. 
            ((WebBrowser)sender).Dispose();
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.ToString());
        }

    }

    private void notifyIcon1_MouseDoubleClick(object sender, MouseEventArgs e)
    {
        this.Show();
        this.Activate();
        if (this.WindowState == FormWindowState.Minimized)
        {
            this.WindowState = FormWindowState.Normal;
        }
    }

    private void Form1_Resize(object sender, EventArgs e)
    {
        if (FormWindowState.Minimized == WindowState)
        {
            Hide();
        }  
    }

如果你们对此有任何见解，我将非常感谢你的帮助！也许我不应该使用WebBrowser打印HTML文件？

Answer 1

FSW引发的事件（如Created）将在工作线程上触发。这非常重要，它确保尽快传递通知，并确保FSW使用的内部缓冲区不会溢出。你应该检查一下btw，不要忘记订阅错误事件。

您在事件处理程序中可以执行的操作是有限的，但是，您始终需要知道您的代码在另一个线程中运行。线程安全始终是一个问题。您在此处遇到的具体错误是由此引起的，WebBrowser不是一个线程安全的类。在少数情况下，您实际上会收到警告，指出您使用的是不支持线程的类，更常见的问题是随机错误行为。

Anyhoo，FSW使解决这个问题非常简单。您可以要求它在UI线程上引发事件。它需要一行代码：

  fsw.SynchronizingObject = this;

请注意，如果事件的频率很高，这将使FSW陷入困境，并且必须保持您的UI线程响应。不要跳过该错误事件。通过线程安全队列技术上可以将FSW与浏览器分离，您可以在this answer的单独线程上找到运行WebBrowser所需的代码类型。

从Web浏览器打印时出现ThreadStateException

1 个答案: