c# opennetCF background worker - e.result gives a ObjectDisposedException
- by ikky
Hi!
I'm new working with background worker in C#.
Here is a class, and under it, you will find the instansiation of it, and under there i will define my problem for you:
I have the class Drawing:
class Drawing
{
BackgroundWorker bgWorker;
ProgressBar progressBar;
Panel panelHolder;
public Drawing(ref ProgressBar pgbar, ref Panel panelBig) // Progressbar and panelBig as reference
{
this.panelHolder = panelBig;
this.progressBar = pgbar;
bgWorker = new BackgroundWorker();
bgWorker.WorkerReportsProgress = true;
bgWorker.WorkerSupportsCancellation = true;
bgWorker.DoWork += new OpenNETCF.ComponentModel.DoWorkEventHandler(this.bgWorker_DoWork);
bgWorker.RunWorkerCompleted += new OpenNETCF.ComponentModel.RunWorkerCompletedEventHandler(this.bgWorker_RunWorkerCompleted);
bgWorker.ProgressChanged += new OpenNETCF.ComponentModel.ProgressChangedEventHandler(this.bgWorker_ProgressChanged);
}
public void createDrawing()
{
bgWorker.RunWorkerAsync();
}
private void bgWorker_DoWork(object sender, DoWorkEventArgs e)
{
Panel panelContainer = new Panel();
// Adding panels to the panelContainer
for(i=0; i<100; i++)
{
Panel panelSubpanel = new Panel();
// Setting size, color, name etc....
panelContainer.Controls.Add(panelSubpanel); // Adding the subpanel to the panelContainer
//Report the progress
bgWorker.ReportProgress(0, i); // Reporting number of panels loaded
}
e.Result = imagePanel; // Send the result(a panel with lots of subpanels) as an argument
}
private void bgWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
this.progressBar.Value = (int)e.UserState;
this.progressBar.Update();
}
private void bgWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
if (e.Error == null)
{
this.panelHolder = (Panel)e.Result;
}
else
{
MessageBox.Show("An error occured, please try again");
}
}
}
Instansiating an object of this class:
public partial class Draw: Form
{
public Draw()
{
ProgressBar progressBarLoading = new ProgressBar();
// Set lots of properties on progressBarLoading
Panel panelBigPanelContainer = new Panel();
Drawing drawer = new Drawing(ref progressBarLoading, ref panelBigPanelContainer);
drawer.createDrawing(); // this makes the object start a new thread, loading all the panels into a panel container, while also sending the progress to this progressbar.
}
}
Here is my problem:
In the private void bgWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
i don't get the e.Result as it should be.
When i debug and look at the e.Result, the panel's properties have this exception message:
'((System.Windows.Forms.Control)(e.Result)).ClientSize' threw an exception of type 'System.ObjectDisposedException'
So the object gets disposed, but "why" is my question, and how can i fix this?
I hope someone will answer me, this is making me crazy.
Another question i have: Is it allowed to use "ref" with arguments? is it bad programming?
Thanks in advance.
I have also written how i understand the Background worker below here:
This is what i think is the "rules" for background workers:
bgWorker.RunWorkerAsync(); => starts a new thread.
bgWorker_DoWork cannot reach the main thread without delegates
-
private void bgWorker_DoWork(object sender, DoWorkEventArgs e)
{
// The work happens here, this is a thread that is not reachable by
the main thread
e.Result => This is an argument which can be reached by
bgWorker_RunWorkerCompleted()
bgWorker.ReportProgress(progressVar); => Reports the progress to the
bgWorker_ProgressChanged()
}
-
private void bgWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
// I get the progress here, and can do stuff to the main thread from here
(e.g update a control)
this.ProgressBar.Value = e.ProgressPercentage;
}
-
private void bgWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
// This is where the thread is completed.
// Here i can get e.Result from the bgWorker thread
// From here i can reach controls in my main thread, and use e.Result in my main thread
if (e.Error == null)
{
this.panelTileHolder = (Panel)e.Result;
}
else
{
MessageBox.Show("There was an error");
}
}
