Question

I have a problem with Bing Maps control I use in my WP7 application.

When I’m navigated to the page with map control, it starts the GeoCoordinateWatcher. When GeoCoordinateWatcher has some location data for me, it calls a SetView() method to center the map at current location. There is also a button on ApplicationBar that’s also starting the GeoCoordinateWatcher.

Now, the thing is, when I first navigate to this page, all works fine: GeoCoordinateWatcher starts, gives me the location data after some time, calls SetView() and the map centers when I need it too. The same with the button.

But if I press the Back button to get back to the main page and then try to navigate again to the map page, SetView() stops working. In debugging I see that the code surrounding it works as expected and the data passed to SetView() is correct, but nothing happens with the control and events for changing view don’t fire either.

I’m assuming there may be something wrong with map initialization (or disposing on navigating from), but I don’t know where to dig.

Edit:
I’ve tried changing Map.Center directly and it doesn’t work in exactly the same way the SetView() doesn’t: it works fine the first time page is navigated to and doesn’t work on the other times.

Edit 2:
Ok, it gets weirder. In debugging I see that my map’s center actually gets set to a correct value. But an actual control shows absolutely different location and me, moving map around, doesn’t change the value that I see from code.

Edit 3:
I’ve added a button to ApplicationBar that just calls SetView() and it works fine. Apparently, the problem appears when I call SetView() as a result of GeoCoordinateWatcher.PositionChanged event raising. How could I work around that?

Answer 1

I’ve found the solution.

In my original code I’ve subscribed to the GeoCoordinateWatcher.Position property change event in the page constructor: App.PropertyChanged += AtmInfoPageOnAppPropertyChanged

All I had to do was to move that to the OnNavigatedTo event handler and add App.PropertyChanged -= AtmInfoPageOnAppPropertyChanged to the OnNavigatedFrom event handler.

I think, the problem was that keeping the old page subscribed to the event didn’t allow it to be disposed, and at the same time didn’t allow the new page to subscribe to that same event, thus causing the code to be called for the different page and different map control than the one displayed on the screen.