Adding hundreds of pushpins programatically to bing maps freezes the WP7 UI

Question

I'm working on a WP7 app that uses bing maps to display ~600 pushpins. When i add them to the map using map.Children.Add(pushpin) the UI freezes for ~200 ms. I've seen that in silverlight you can use Microsoft.Maps.EntityCollection to add pins to a map but unfortunately I couldn't find how to use the assembly on WP7. Does anyone know a solution to this?

Answer 1

Maybe you're looking at the problem the wrong way round. WP7 is a compact (though powerful) that excels at showing the user what they want to know quickly (when the apps are written properly).

The user can't possibly see 600 pushpins in one go on a device that small, so why not just show them pushpins that are in the viewable area (or close to it) and add pushpins as the user pans around the map?

Alternatively you could "trickle" feed the pushpins by adding them one (or more) at a time using the DispatcherTimer so that the user sees pushpins being gradually added without drastically affecting performance.

Another possibility (which is what I usually do) is to add a MapItemsControl with the DataTemplate set to a Pushpin and to bind the collection to your collection of pushpin locations. If the binding is to an ObservableCollection you can "trickle" feed it as mentioned above if perf is an issue.

Answer 2

In a viewpoint similar to Derek's, I find it highly unlikely that you seriously want to put 600 pins on the screen at the same time . I'm guessing that they span a large geographic area and the user is unlikely to see more than a handful at a time.

If this is the case, you can trivially apply a cliprect to cull your points, then add the resultant modest list to a layer, and Presto. High performance.

In addition, there is the issue of what to do when the user zooms a long way out, bringing so many pins into view that they merge into one big useless but brightly coloured blob. This is a more complex problem traditionally solved with a quadtree, and I have a suspicion that you just said "a what?" but luckily Google is your friend.

Oh, and to address your stated problem - don't add the pins directly to a map. Add them to a MapLayer and then add that.