Question

This may seem like a somewhat contrived example, but I’m left scratching my head.

Ok, I have a console app that instantiates a WindowsForm and calls a method called DoSomeWork() on the form.

class Program   {      static void Main(string[] args)     {       Form1 form = new Form1();                form.DoSomeWork();        }   } 

Form1 looks like this…

public partial class Form1 : Form   {     public Form1()     {       InitializeComponent();     }      public void DoSomeWork()     {       OuterClass outerClass = new OuterClass();       outerClass.DoSomeWork();     }       } 

Outer class, in turn, looks like this…

public class OuterClass   {     public void DoSomeWork()     {       InnerClass innerClass = new InnerClass();       innerClass.DoSomeWork();     }   } 

And finally InnerClass looks like this…

public class InnerClass   {     private BackgroundWorker _backgroundWorker = new BackgroundWorker();      public InnerClass()     {       _backgroundWorker.WorkerReportsProgress = true;       _backgroundWorker.DoWork += new DoWorkEventHandler(BackgroundWorker_DoWork);       _backgroundWorker.ProgressChanged += new ProgressChangedEventHandler(BackgroundWorker_ProgressChanged);     }      void BackgroundWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)     {       int i = 0; //I've placed a break point here. But it's never hit     }      void BackgroundWorker_DoWork(object sender, DoWorkEventArgs e)     {       BackgroundWorker worker = sender as BackgroundWorker;        worker.ReportProgress(42);     }      public void DoSomeWork()     {       _backgroundWorker.RunWorkerAsync();     }   } 

For a reason unknown (to me), the BacgroundWorker in InnerClass never seems to fire the ProgressChanged event. If I replace

Form1 form = new Form1(); 

with

OuterClass outerClass = new OuterClass() 

in class Program, it works fine. So why is that my events don’t fire when I’m calling the same methods through a Form?

Thanks!

EDIT: I seemed to be throwing people off by leaving the ProgressChanged event handler as throwing a NotImplementedException, so I’ve removed it for clarity.

Answer 1

You forgot to start a message loop, calling Application.Run() is required. Without a message loop, the BackgroundWorker events cannot work. To fix:

static void Main(string[] args) {   Application.Run(new Form1());    } 

Call DoSomeWork() in the form’s constructor or it’s Load event.