C# - 后台 worker ？

Question

我有一个相当复杂的程序，所以我不会在这里转储整个程序。这是一个简化版本:

class Report {
    private BackgroundWorker worker;

    public Report(BackgroundWorker bgWorker, /* other variables, etc */) {
        // other initializations, etc
        worker = bgWorker;
    }

    private void SomeCalculations() {
        // In this function, I'm doing things which may cause fatal errors.
        // Example: I'm connecting to a database.  If the connection fails, 
        // I need to quit and have my background worker report the error
    }
}


// In the GUI WinForm app:
// using statements, etc.
using Report;

namespace ReportingService {
    public partial class ReportingService : Form {

        // My background worker
        BackgroundWorker theWorker = new BackgroundWorker() {
            WorkerReportsProgress = true
        };

        // The progress changed event
        void worker_ProgressChanged(object sender, ProgressChangedEventArgs e) {
            // e.UserState and e.ProgressPercentage on some labels, etc.
        }

        // The do work event for the worker, runs the number crunching algorithms in SomeCalculations();
        void worker_DoWork(object sender, DoWorkEventArgs e) {
            Report aReport = e.Argument as Report;

            aReport.SomeCalculations();
        }

        // The completed event, where all my trouble is.  I don't know how to retrieve the error,
        // or where it originates from.
        void worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) {
            // How, exactly, do I get this error message? Who provides it? How?
            if (e.Error != null) {
                MessageBox.Show("Error: " + (e.Error as Exception).ToString());
            }
            else if (e.Cancelled) {
                MessageBox.Show("Canceled");
            }
            // operation succeeded
            else {
                MessageBox.Show("Success");
            }
        }

        // Initialization of the forml, etc
        public ReportingService() {
            InitializeComponent();

            theWorker.ProgressChanged += worker_ProgressChanged;
            theWorker.DoWork += worker_DoWork;
            theWorker.RunWorkerCompleted += worker_RunWorkerCompleted;
        }

        // A button that the user clicks to execute the number crunching algorithm
        private void sumButton_Click(object sender, EventArgs e) {
            Report myReport = new Report(theWorker, /* some other variables, etc */)
            theWorker.RunWorkerAsync(myReport);
        }
    }
}

这是我的逻辑，如果我以错误的方式进行此操作，请纠正我:

1. 我从 GUI 中抽象出该类，因为它大约有 2000 行，并且需要成为它自己的自包含对象。

2. 我将后台工作人员传递到我的类(class)，以便我可以报告我的数字处理进度。

我不知道如何做的是让后台工作人员知道我的类(class)内部发生了错误。为了获得 RunWorkerCompleted 参数作为异常，我的 try/catch block 需要去哪里，我应该在 catch block 中做什么？

感谢您的帮助!

编辑:

我尝试了以下方法来测试错误处理:

请记住，我损坏了我的数据库连接字符串是为了故意接收一条错误消息。

在我的类里面我这样做:

// My number crunching algorithm contained within my class calls a function which does this:

// try {
    using (SqlConnection c = GetConnection()) {  // note: I've corrupted the connection string on purpose
        c.Open();  // I get the exception thrown here
        using (SqlCommand queryCommand = new SqlCommand(query, c)) { /* Loop over query, etc. */ }
        c.Close();  
    }
// } catch (Exception e) { }

1.根据我的理解，未处理的异常被转换为 RunWorkerCompletedEventArgs 的 Error 部分？当我尝试这个时，我得到以下信息:

// In my winform application I initialize my background worker with these events:

void gapBW_DoWork(object sender, DoWorkEventArgs e) {
    Report aReport = e.Argument as Report;
    Report.Initialize();    // takes ~1 minute, throws SQL exception
    Report.GenerateData();  // takes around ~2 minutes, throws file IO exceptions
}

void gapBW_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) {   
    if (e.Error != null) {  // I can't get this to trigger, How does this error get set?
        MessageBox.Show("Error: " + (e.Error as Exception).ToString());
    }
    else if (e.Cancelled) {
        MessageBox.Show("Canceled: " + (e.Result).ToString());
    }
    else {
        MessageBox.Show("Success");
    }
}

Visual Studio 说我的应用程序因未处理的异常而因 c.Open() 而阻塞。

2。当我在我的 DoWork 函数中放置一个 try/catch block 时:

void gapBW_DoWork(object sender, DoWorkEventArgs e) {
    try {
        Report aReport = e.Argument as Report;
        aReport.Initialize();   // throws SQL exceptions
        aReport.GenerateData(); // throws IO file exceptions
    }
    catch (Exception except) {
        e.Cancel = true;    
        e.Result = except.Message.ToString();
    }
}

void gapBW_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) {   
    if (e.Error != null) {  // I can't get this to trigger, How does this error get set?
        MessageBox.Show("Error: " + (e.Error as Exception).ToString());
    }
    else if (e.Cancelled) {
        MessageBox.Show("Canceled: " + (e.Result).ToString());
    }
    else {
        MessageBox.Show("Success");
    }
}

我在自动生成的 Application.Run(new ReportingService()); 行的 Program.cs 中收到 TargetInvocationException was unhandled。我在 RunWorkerCompleted 上放置了一个断点，可以看到 e.Cancelled = true、e.Error = null 和 e.UserState = null。 e.Cancelled 中包含的消息只是“操作已被取消”。我想我正在从 e.Result 的无效转换中接收到 TargetInvocationException(因为它为 null)。不过，我想知道的是，为什么 e.Error 仍然为 null 而 e.Canceled 不包含有关为什么操作被取消的任何有用信息？

3。当我尝试在异常捕获时从 DoWork 中设置 e.Canceled = true; 时，我设法触发了我的 中的 else if (e.Cancelled) { 行>RunWorkerCompleted 函数。我以为这是为请求取消作业的用户保留的？我是否从根本上误解了后台工作人员的工作方式？

Answer 1

我尝试了这个小测试程序，它按预期工作:

static void Main(string[] args)
{
    var worker = new BackgroundWorker();

    worker.DoWork += (sender, e) => { throw new ArgumentException(); };
    worker.RunWorkerCompleted += (sender, e) => Console.WriteLine(e.Error.Message);
    worker.RunWorkerAsync();

    Console.ReadKey();
}

但是当我在调试器中运行该程序时，我还在 throw 语句中收到了有关未处理异常的消息。但我只是再次按下 F5，它继续没有任何问题。