Question

我已经构建了一个可以监控打印作业的C＃WPF应用程序。一切正常。我可以打印文档并监视其打印作业。

但每次我点击＆＃34;打印表格＆＃34;按钮，触发＆＃34;打印作业更改＆＃34;事件，我在“输出”面板中三次收到消息Exception thrown: 'System.NotSupportedException' in PresentationCore.dll（请参阅下面的更多消息）。起初我认为它来自控制台日志代码，例如Console.Write或Console.WriteLine，但是当我检查它们时，我的程序没有。

所以我查看了什么是System.NotSupportedException here。

我明白了

不支持调用的方法时，或者尝试读取，搜索或写入不支持调用的功能的流时抛出的异常。

然后我记得在我的＆＃34;关于打印工作的变化＆＃34;事件处理程序，我有一些语句从不同的线程调用对象（我不知道这个术语是什么）。然后我尝试禁用每个有调用的行。但是当应用程序再次运行时，消息仍然存在。

以下是“输出”面板中的完整消息，该消息来自＆＃34;打印表单＆＃34;按钮（在第二次点击之后，它没有显示第一行和最后两行）：

'PrintClientWPF.vshost.exe' (CLR v4.0.30319: PrintClientWPF.vshost.exe): Loaded 'Anonymously Hosted DynamicMethods Assembly'. 
Exception thrown: 'System.NotSupportedException' in PresentationCore.dll
Exception thrown: 'System.NotSupportedException' in PresentationCore.dll
Exception thrown: 'System.NotSupportedException' in PresentationCore.dll
The thread 0x1f18 has exited with code 0 (0x0).
The thread 0x272c has exited with code 0 (0x0).

这是＆＃34;关于打印作业更改的事件处理程序＆＃34;事件：

public async void PrintHelperInstance_PrintJobsChange(object sender, EventArrivedEventArgs e)
{
    ManagementBaseObject objProps = (ManagementBaseObject)e.NewEvent.Properties["TargetInstance"].Value;

    string instanceOperation = e.NewEvent.SystemProperties["__Class"].Value.ToString();
    string jobName = objProps["Document"].ToString();

    if (JobNameList.Contains(jobName))
    {
        if (!IsFoundPrintJob)
        {
            IsFoundPrintJob = true;
        }

        CurrentJobStatus = (string)objProps["JobStatus"];

        if (CurrentJobStatus != PreviousJobStatus)
        {
            uint jobId = (uint)objProps["JobId"];
            string jobDriver = (string)objProps["DriverName"];
            string jobHost = (string)objProps["HostPrintQueue"];
            string jobStatus = (string)objProps["JobStatus"];

            // Use Dispatcher.Invoke to execute statements from a thread other than the main thread
            this.Dispatcher.Invoke(() =>
            {
                string printerName = PrintHelperInstance.GetPrintQueueFromQueueDriverName(jobDriver).Name;
                string msg = string.Format("ID: {0}, Name: {1}, Printed on: {2}, Host: {3}, Status: {4}",
                    jobId, jobName, printerName, jobHost, jobStatus);

                TextBlockPrintJobStatus.Text += msg + System.Environment.NewLine;
            });

            PreviousJobStatus = CurrentJobStatus;
        }
    }

    // Indicates that the print job has been deleted
    if (IsFoundPrintJob && instanceOperation == "__InstanceDeletionEvent")
    {
        this.Dispatcher.Invoke(() =>
        {
            TextBlockPrintJobStatus.Text += "Print completed" + System.Environment.NewLine;
        });

        IsFoundPrintJob = false;

        string postResponse = "";

        try
        {
            // TODO: Not implemented yet, just testing here
            postResponse = await ApiHelperInstance.Post(new KeyValuePair<string, string>("id", "1"));
        }
        catch (HttpRequestException ex)
        {
            this.Dispatcher.Invoke(() =>
            {
                TextBlockPrintJobStatus.Text += "HTTP Request Error: " + ex.Message + System.Environment.NewLine;
            });
        }
        catch (Exception ex)
        {
            this.Dispatcher.Invoke(() =>
            {
                TextBlockPrintJobStatus.Text += "Exception: " + ex.Message + System.Environment.NewLine;
            });
        }
        finally
        {
            this.Dispatcher.Invoke(() =>
            {
                TextBlockPrintJobStatus.Text += postResponse + System.Environment.NewLine;
            });
        }
    }
}

其实我是C＃的新人，而且我对这类事情没有高级知识。

所以我的问题是，为什么会出现异常消息和我该如何摆脱它？

＆＃39; System.NotSupportedException＆＃39;在PresentationCore.dll中出现在“输出”面板中

0 个答案: