Windows Phone 7 - Bing Maps MVVM Pushpin initialization - mvvm

Question

Does anyone have a good guideline on how to initialize a pushpin on the Bing Maps control?
My current scenario works, but is not 100% correct... let me explain the details:
When I open the page with the Bing Maps control on it, I want the user to be able to push a small button that will show his current location.
To show the current location, I'm using a Pushpin. I'm already adding the Pushpin on the control in the XAML file like this:
<map:Pushpin> x:Name="currentLocation" Location="{Binding CurrentLocation}" Content="Me" ManipulationStarted="CurrentLocationPin_ManipulationStarted" </map:Pushpin>
Now with this scenario there a some problems!
One, the pushpin is always visible! So how do I go about this? ( I know I can bind the Visibility also to a property and use a bool to visibility converter, but is this the best way to do this? )
Secondly, now I don't initialize the Location in the viewmodel... but for semantic reasons I would love to initialize the default value to Geocoordinate.Unkown ( that way I can use this to do checks when the user tries to do some manipulation before a currentlocation is set ). But when I initialize the pushpin on startup I get following error: "UIElement.Arrange(finalRect) cannot be called with Infinite or NaN values in finalRect.". So my question again :) what is a good guideline to setting up a currentlocation pushpin? ( but do mind that the users has to push a small application bar button before the currentlocation is set )

Answer 1

The initialization problem is due to the visibility of the Pushpin. If the initial visibility of the Pushpin is Collapsed, then it won't take part in the arrange pass, so you won't get the error.
If you're using a view model to back this view, then I don't see a problem with exposing a property from the view model that determines whether the Pushpin should be visibile or not. Yes you could use a boolean to visibility converter, but you could save some processing by actually exposing a Visibility property (which is the approach I've used).
If you're using a command to initiate showing the Pushpin from the button push (the Silverlight Windows Phone Toolkit has a behavior to enable hooking up application bar buttons to commands).