dynamic controls - Page 296

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"); } }

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