Dispatcher.BeginInvoke error in App.xaml file

06-10-2008 8:00 PM |

Hi,

I wish to read xml files available in my Silverlight Web hosting project in the App.xaml file and then call the Page.xaml file once reading is done using web client. But i am getting error "Invalid cross-thread access". This approach was working fine in Beta 1. I have to read all the xml files before page SL pages are displayed. My code in App.xaml.cs file:

public App()

{

this.Startup += this.Application_Startup;

this.Exit += this.Application_Exit;

this.UnhandledException += this.Application_UnhandledException;

ThreadStart start = new ThreadStart(NonUIWork);

Thread thread = new Thread(start);

thread.Start();

InitializeComponent();

}

void NonUIWork()

{

//BELOW LINE GIVES ME AN ERROR: Invalid cross thread access

this.RootVisual.Dispatcher.BeginInvoke(() =>

{

DoSomething();

}

);

}

void DoSomething()

{

HttpWebRequest xmlCommonData = (HttpWebRequest)WebRequest.Create(new Uri(GetAppPath() + "XML/Common.xml"));xmlCommonData.BeginGetResponse(new AsyncCallback(CommonDataResponseCallBack), xmlCommonData);

}

.......

 

regards,

Parimal

Re: Dispatcher.BeginInvoke error in App.xaml file

06-10-2008 8:24 PM |

Hey,

The exception is thrown from RootVisual getter (the RootVisual property also cannot be accessed from non-UI thread). The solution is to store the dispatcher somewhere before the second thread is started:

private Dispatcher _dispatcher; 
public App()
{
    this.Startup += this.Application_Startup;
    this.Exit += this.Application_Exit;
    this.UnhandledException += this.Application_UnhandledException;
    
    InitializeComponent();    
    ThreadStart start = new ThreadStart(NonUIWork);
    Thread thread = new Thread(start);
    thread.Start();

   _dispatcher = RootVisual.Dispatcher;
}

void NonUIWork()
{
   _dispatcher.BeginInvoke(() => { … });
}

Regards,
Tomek

Re: Dispatcher.BeginInvoke error in App.xaml file

06-10-2008 8:53 PM |

Thanks for the response.

In which namespace i can get the Dispatcher object as it is not resolving the App.xaml.cs file?

regards,

Parimal

Re: Dispatcher.BeginInvoke error in App.xaml file

06-10-2008 8:59 PM |

It's in System.Windows.Threading. Useful tip - when you type class name, press Ctrl + . (dot), and Visual Studio will display menu allows to add approriate using automatically.

Regards,
Tomek

Re: Dispatcher.BeginInvoke error in App.xaml file

06-10-2008 9:10 PM |

Thanks for the response once again.

I wish to call Page.xaml from App.xaml.cs file. But before that i wish to read all the xml files in my app using web client. Where [method] should i call the Page class in the App.xaml.cs file so that it gets called after i finish my XML reading. If i put it in DoSomething method, it gets called first that the App_Startup method. If i put it in App_Starup event, it calls first here also. I wish to call the "

this.RootVisual = new Page();" method after i finish my xml reading in app.xaml.cs file?

regards,

Parimal

Re: Dispatcher.BeginInvoke error in App.xaml file

06-27-2008 9:54 AM |

SL2B2 runs comm callbacks in threads that are drawn from a thread pool -- it doesn't make any difference what thread you begin the request from.  The following article talks about effective patterns for using the Dispatcher object:

 http://gen5.info/q/2008/06/25/getting-back-to-the-ui-thread-in-silverlight-2/

Re: Re: Dispatcher.BeginInvoke error in App.xaml file

01-26-2009 8:22 PM |

Try System.Windows.Deployment.Current.Dispatcher.BeginInvoke(...)

Re: Re: Dispatcher.BeginInvoke error in App.xaml file

02-12-2009 12:40 PM |

Thanks a ton vplusplus!

Re: Dispatcher.BeginInvoke error in App.xaml file

05-19-2009 10:38 AM |

These appears to be a permission issue. What version of IIS are you using?

 

 

 

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