Adding a webbrowser control to a form and having it run in a seperate thread?

James Wilcock

16y9.1kC#

I am trying to achieve the display of an animated gif in a windows app. I had hoped that by displaying it in a webbrowser contro that it would always be animated.

Currently it is only animated when the system is not busy however when the app is processing such as returning data the animation freezes. To prevent this wouldit be possible to get the webbrowser control to run in a different thread, and could this solve my problem?

However I am getting hte error

Cross-thread operation not valid: Control 'uctrlBusyDisplay' accessed from a thread other than the thread it was created on.

   public uctrlBusyDisplay()
        
{
            
InitializeComponent();
            
Thread t = new Thread(new 
ThreadStart(DoIt));
            
t.SetApartmentState(ApartmentState.STA);
            
t.Start();            


          

        }
 private void 
DoIt()
         { 

             
WebBrowser wb = new 
WebBrowser();
             
wb.Location = new Point(20, 
10);
             
wb.Navigate("www.google.co.uk");
             
this.Controls.Add(wb);
          

            


         }

The error seems to occur when I try and add the webbrowser control to the usercontrol.

this.Controls.Add(wb);

 Action a = () => { Controls.Add(wb); 
};
            

            
Invoke(a);

I have triebut still get the error as I dont really understand the method.
Also jumping ahead to when I have achieved this when I have added the control will the webbrowser still control be running in its own thread when it is added to the main form?

11 Replies

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Sam Hobbs16y ago
Instead of ignoring the progress bar control based on your understanding, look at the documentation and get a better understanding.

James Wilcock16y ago

Its my understanding that the progress control would have the same problem you can only increment the progress bar when you have cpu time i.e via a loop etc.
Obj controlFactors is a UserControl which I have added to my form, it is the control upon which the animation is shown.
Anyway I guess I have digressed now from the animation problem and all I want to do now is execute my get data method (which takes a parameter) in a new thread.
Or perhaps using a progress bar I could use this
http://www.codeguru.com/columns/vb/article.php/c10755
If I could convert to C#

 

worker = new System.ComponentModel.BackgroundWorker();

worker.WorkerReportsProgress = true;

worker.DoWork += new EventHandler 
DoWorkEventHandler(AddressOf OnWork)

worker.ProgressChanged += new ProgressChangedEventHandler(AddressOf OnProgressChanged)

Right now its not liking the delegate.

 

private void 
OnProgressChanged(object sender,ProgressChangedEventArgs e)

{ Invoke(ChangeProgressBarHandler(ChangeProgressbar), 
e.ProgressPercentage));

}

Sam Hobbs16y ago
You don't show what objCtrlFactors is.
Sam Hobbs16y ago
Sorry, I did not realize that you are using an animated GIF. I am not sure why the animated GIF stops, but use of an animated GIF for the purpose you are using it is not what they were designed to do.

I think the ProgressBar is capable of showing animation; have you looked at that?

Also, you should use the BackgroundWorker class; it is designed to be easier to use.
James Wilcock16y ago
Sorry I agree in that respect it does occur due to time, the cpu has to process each frame over time. When the cpu is busy it cannot process the next frame to the animation is frozen. This is why I want to start a new thread to run get data method enabling both threads to share the cpu time and process both sets of requests.
James Wilcock16y ago
My problem now is that Im new to threading and my simple line of code in bold doesnt work.
I think it is most likely because i am trying to pass a parameter through to the method im trying to invoke in the new thread, which it doesnt seem to like.

James Wilcock16y ago

Neither, The animation is always the same i.e. just some arrows moving in a circular fashion.
I want the animation (the browser control) to be invisible. When the user presses the button to return some data I will make the animation visible.
I think at this point I will strat a new thread to call the getdata method
Once the getdata method has completed I will make the webbrowser control invisible again.
So I think I am looking at some thing like this.

 void btnRefresh_Click(object sender, EventArgs e) 
{ 

try 
{ 
objReportAudit.AuditUpdate(); 

this.objCtrlFactors.ShowImage(); 

this.factors = 
objCtrlFactors.GetFactors(this.reportVersion); 
if 
(factors.IsValid) 
{ 
this.objCtrlFactors.btnRefresh.Enabled = false; 

myThread = new Thread(new ThreadStart(this.GetData(factors);)); 
this.GetData(factors); 

objReportAudit.AuditUpdate(); 
} 
else 
{ 

MessageBox.Show(factors.ValidationMessage, 
"Factors validation 
error", MessageBoxButtons.OK, 
MessageBoxIcon.Hand, MessageBoxDefaultButton.Button1); 
} 
} 

catch (Exception ex) 
{ 

objReportAudit.AuditUpdate(ex.Message.ToString()); 
Error.ReportError(Properties.Settings.Default.Corp_RptConnectionString, objReportAudit.GetAuditID(), 
Globals.ThisWorkbook.Name, 
objReportAudit.GetUsername(), ex); 
} 
finally 
{ 
this.objCtrlFactors.btnRefresh.Enabled = 
true; 
this.objCtrlFactors.HideImage(); 
} 
} 

public void 
GetData(Factors f) 
{ 

Excel.Application excelApp = this.Application; 
excelApp.Cursor = 
Excel.XlMousePointer.xlWait; 
excelApp.StatusBar 
= "Executing 
database query"; 
Excel.Workbook 
newWorkbook; 
string newWorkbookName = ""; 

try 
{ 
DAL.GetData(ds, f); 

Globals.ThisWorkbook.Activate(); 

excelApp.ScreenUpdating = false; 
newWorkbook = 
ReportRender.CopyToNewWorkbook(this.Application, Globals.ThisWorkbook.Sheets, Globals.ThisWorkbook.Name); 
this.WriteReportTitle((Excel.Worksheet)newWorkbook.Worksheets["Usage"]); 
ReportRender.GenericDrawRoutine((Excel.Worksheet)newWorkbook.Worksheets["Usage"], (DataTable)Globals.ThisWorkbook.ds.UP_CRSUsageAudit, 
columnMappings, functionMappings, "A8"); 
newWorkbookName = 
newWorkbook.Name; 
Marshal.ReleaseComObject(newWorkbook); 

newWorkbook = null; 
} 
finally 
{ 

Thread.Sleep(2000); 
excelApp.Cursor = 
Excel.XlMousePointer.xlDefault; 

excelApp.ScreenUpdating = true; 
excelApp.StatusBar = 
"Ready"; 
Marshal.ReleaseComObject(excelApp); 
excelApp = null; 

GC.Collect(); 
GC.WaitForPendingFinalizers(); 
GC.Collect(); 
GC.WaitForPendingFinalizers(); 
} 
}

Sam Hobbs16y ago
It is extremely easy to use a boolean flag to determine if the thread is already executing. There are many other things that could be done. You could disable the button so it can't be clicked.

I don't think you have specified whether the animation changes due to time or due to progress.
James Wilcock16y ago
OK so when I press the button I should make visible my gif then start a new thread to return the data. I think I could do that.
In terms of threading do I need to kill the threads when the data has been returned? If the user presses the get data button numerous times is it risky to be spawning lots of new threads?
James Wilcock16y ago
Well if I place the control directly onto the form and it is running in the main thread as soon as the system is busy i.e. querying data then the animation stops. This is the reverse of what I want to achieve. I am trying to simulate to the user that the application is processing by displaying the animated gif.
Maybe there is a better way to achieve this?
Sam Hobbs16y ago
You don't need a separate thread for that and Windows does not support use of a control in a thead that does not own the control.