c# - 在多线程应用程序中使用 MessageBox 显示异常信息

Question

您好，我正在使用 winform 并尝试使用 MessageBox 进行异常处理。奇怪的是，MessageBox 仅在主窗体(下面代码中的“Form1”)关闭后出现。

public class Worker {
    /* edited (see below)
    public void doWork() {
        try {
            // do something
            client.Connect(serverAddress);
            stream = client.GetStream();
        }
        catch(Exception e) {
            MessageBox.Show(e.ToString(), 
                "This will not show up until Form1 is closed");
        }
    }
    */
}

public class Form1 {
    /* edited (see below)
     * public void threadProc() {
     *    Worker worker = new Worker();
     *    worker.doWork();
     * }
     */
     void button_Click(object sender, EventArgs e) {
        // create a thread that will end up throwing an exception
        Thread thread = new Thread(threadProc);
        thread.Start();
     }
}

使用 MessageBox 进行异常处理的更好方法是什么？

---

...所以我在 UI 线程中添加了一些用于 MessageBox-ing 的代码，但问题仍然存在。

public class WorkExceptionArgs : EventArgs {
    public Exception e;
    public WorkExceptionArgs (Exception e) { this.e = e; }
}
public partial class Worker1 { // renamed (Worker->Worker1)
    /* (edited) Now Worker1 doesn't trigger any event (see below)
       public event EventHandler<WorkExceptionArgs> workException;
    */
    public void doWork() {
        try {
            // do something
            client.Connect(serverAddress);
            stream = client.GetStream();
        }
        catch(Exception e) {
            /* (edited) suppose Worker1 never throws any exception (see below)
             *  // trigger event that will cause MessageBox-ing by UI thread
             *  workException(this, new WorkExceptionArgs(e));
             */
        }
    }
}
public partial class Form1 {
    public void threadProc() {
       Worker1 worker1 = new Worker();
      /* (edited) Now Worker1 never throws any exception
       * worker.workException += new EventHandler<WorkException>(worker_WorkException);
       */
       worker1.doWork();
       // (added) After doWork() is done, Form1 creates Worker2
       Worker2 w2 = new Worker2(this, this.form2);
       w2.workException += new EventHandlerArgs<WorkExceptionArgs>(form2.worker2_WorkException);
       w2.doSomeOtherWork();
    }
    /* public void worker_WorkException(object sender, WorkExceptionArgs eArg) {
     *   MessageBox.Show(eArg.e.ToString(), "Still not showing");
     * } */
    Form2 form2 = new Form2(); // (added) At first form2 is hidden (see below)
}

---

实际上已经有另一种形式和另一种 worker 。一旦 Worker(Worker1) 连接到服务器，Form1 隐藏 (.Hide())，Form2 显示 (.Show())，Worker2 开始使用 Worker1 建立的连接。

public class Worker2 {
    Worker2(Worker1 w1, Form2 frm2) { this.w1=w1; this.frm2=frm2; }
    public Worker1 w1;
    public Form2 frm2;
    public event EventHandler<WorkExceptionArgs> workException;
    public void doSomeOtherWork() { // do some other, using data in Worker 1.
        try { // This will throw an exception
            BinaryFormatter formatter = new BinaryFormatter();
            MyObj mo = (MyObj)formatter.Deserialize(w1.getStream());
        }
        catch(Exception e) {
            workException(this, new WorkExceptionArgs(e));
        }
    }             
}

public class Form2 {
    public Form2(Form1 frm1) { // to switch from frm1 to frm2
        InitializeComponent();
        this.frm1 = frm1;
    }
    public Frm1 frm1 {get;set;}
    public void worker2_WorkException(object sender, WorkExceptionArgs ea) {
       MessageBox.Show(this, ea.e.ToString(), "SHOWS ONLY IF FORM2 IS CLOSED");
    }

}     

public partial class Form1 {
    delegate void switchWindow_Callback();
    public void switchWindow() { this.Hide(); form2.Show(); }
    public void switchWindowCb(object sender, EventArgs e) {
        if(this.InvokeRequired) {
            SwitchWindow_Callback hcb = new SwitchWindow_Callback(switchWindow);
            this.Invoke(hcb, new object[] {});
        }
        else { this.switchWindow(); }
    }
}

Answer 1

实际上，我敢打赌 MessageBox 出现在主窗体后面，只有在关闭它之前您才会看到它。

最好让 UI 线程(创建并拥有 Form1 的线程)执行 MessageBox-ing。您要么想要创建事件，要么在您的工作类中有一个错误回调委托(delegate)。

但是，BackgroundWorker 可能值得在这里检查，而不是尝试自己动手。假设这是一个致命异常，您可以保存和检索错误状态，并在线程结束时自动调用一个事件。