Question

So I am trying to do a very simple thing in WP7 like:

A button in MainPage will launch camera, and when camera successfully take a picture, I want to pass the picture to SecondPage and launch it.

Here’s my code:

Within the MainPage constructor, I initialize the camera task and set the delegate:

camTask.Completed += new EventHandler<PhotoResult>(camTask_Completed);

Then I implemented the camTask_Completed

 void camTask_Completed(object sender, PhotoResult e)
    {
        //throw new NotImplementedException();
        
        img = PictureDecoder.DecodeJpeg(e.ChosenPhoto);
        NavigationService.Navigate(new Uri("/SecondPage.xaml", UriKind.Relative));
    }

The application will run without error until after I pressed "accept" after I took the picture.

The exception says:

Exception {"Navigation is not allowed when the task is not in the foreground."} System.Exception {System.InvalidOperationException}

Which I understand is that I shouldn’t launch the SecondPage within the camTask_Completed method.

Then my question is: How to launch another page on the result of EventHandler?

Thanks

UPDATE: (For answer to this sub-question, please refer to this comment in this page)

I found another error right after I click the button(to launch the camera):

It throw an exception said:

"Type 'System.Windows.Media.Transform' cannot be serialized. Consider marking it with the DataContractAttribute attribute, and marking all of its members you want serialized with the DataMemberAttribute attribute."

Where could I serialize the Transform stuff?

I did some search on Google and found this:

Found the answer, the error actually suggests it too 🙂

[DataContract]

[KnownType(typeof(System.Windows.Media.MatrixTransform))]

Seemed it can resolve this problem, but where should I put these lines?

This is my code on MainPage to pass the image to SecondPage, img is a WriteableBitmap:

 protected override void OnNavigatedFrom(System.Windows.Navigation.NavigationEventArgs e)
    {
        base.OnNavigatedFrom(e);
        var brush = new ImageBrush();
        brush.ImageSource = img;
        PhoneApplicationService.Current.State["bkg"] = brush;
    }

Thanks again.

Answer 1

Perhaps You should try to use the dispatcher:

activePage.Dispatcher.BeginInvoke(
     () => NavigationService.Navigate(new Uri("/SecondPage.xaml", UriKind.Relative)));

This works in MetroApps.