How to call MessageBox within photochooser task - windows-phone-7

Question

I have a code where I am calling photochooser in WP7 and I want to show a messagebox to user when the pic is more than 2Mb. When I try to do this, since the photochooser task is running in background, we start getting unhandled exceptions.
void photoChooserTask_Completed(object sender, PhotoResult e)
{
if (e.ChosenPhoto != null)
{
ProgressBar.Visibility = Visibility.Visible;
image = _UploadImgeViewModel.ReadToEnd(e.ChosenPhoto);
if (image.Length < 16384)
{
BitmapImage bi = new BitmapImage();
bi.SetSource(e.ChosenPhoto);
UserSession.ProfileImage = bi;
Session.PreviousImage = bi;
UserSession.isImageChanged = true;
UserSession.image = image;
UserSession.Uploadimage = image;
NavigationService.Navigated += new NavigatedEventHandler(navigateCompleted);
}
else
{
ProgressBar.Visibility = Visibility.Collapsed;
UserSession.isImageChanged = false;
UserSession.ProfileImage = null;
Dispatcher.BeginInvoke(() => MessageBox.Show("The message"));
}
}
}
#endregion
This only shows the background job as resuming... and the msg box in foreground. and after a few seconds, the app crashes.
Can you please help me with this?

Answer 1

Cool. I got some idea to resolve this. Might not be a fix, but this way we can avoid this issue. Just add a button and do the validating process in the button click event. Since we can't display the message box when the navigation is in progress.
Below is the code:
void photoChooserTask_Completed(object sender, PhotoResult e)
{
if (e.ChosenPhoto != null)
{
ProcessSelectedImage(e.ChosenPhoto);
}
}
private void ProcessSelectedImage(Stream stream)
{
if (stream != null)
{
bi.SetSource(stream);
UserSession.ProfileImage = bi;
UserSession.PreviousImage = bi;
image = ConvertToImage.ReadToEnd(stream);
UserSession.image = image;
UserSession.Uploadimage = image;
}
}
private void UploadImage_Click(object sender, RoutedEventArgs e)
{
if (image.Length < 16384)
{
UserSession.isImageChanged = true;
UserSession.image = image;
UserSession.Uploadimage = image;
NavigationService.Navigate(new Uri("/Views/EditMyProfile.xaml", UriKind.Relative));
}
else
{
UserSession.isImageChanged = false;
UserSession.ProfileImage = null;
UserSession.IsChangingProfilePicture = true;
MessageBox.Show(MessageContent.ImageUploadLengh);
}
}
Thanks
Kamal

Answer 2

You have 10 seconds to return to the foreground completely or your app will be killed. If you have a messagebox that can display here, you will fail certification (because user could not click anything for 10 seconds) -- you need to wait for the page to load.
A workaround for this if you need to show a MessageBox is to set a bool, and check it in the Page's Loaded event.
void photoChooserTask_Completed(object sender, PhotoResult e) { if (e.ChosenPhoto != null) { ProgressBar.Visibility = Visibility.Visible;
image = _UploadImgeViewModel.ReadToEnd(e.ChosenPhoto);
if (image.Length < 16384)
{
BitmapImage bi = new BitmapImage();
bi.SetSource(e.ChosenPhoto);
UserSession.ProfileImage = bi;
Session.PreviousImage = bi;
UserSession.isImageChanged = true;
UserSession.image = image;
UserSession.Uploadimage = image;
NavigationService.Navigated += new NavigatedEventHandler(navigateCompleted);
}
else
{
ProgressBar.Visibility = Visibility.Collapsed;
UserSession.isImageChanged = false;
UserSession.ProfileImage = null;
//set flag
UserSession.ImageTooBig = true;
}
}
}
#endregion
MyPage()
{
//make sure you attach Loaded Event if not already
Loaded += (s,e) =>
{
if (UserSession.ImageTooBig)
{
UserSession.ImageTooBig = false;
MessageBox.Show("Sorry, the image exceeds 2 MB");
}
};
}