Parameterized Constructor for WinRT UserControl - windows-8

Question

I am trying to create a custom Pushpin for Bing Maps in my WinRT application. My problem is that I need a reference to the actual Map from my page in order to pin the icons correctly in my userControl. So for example this is my DataTemplate which gets bound to the map and works fine for the normal pushpins. For my custom userControl to position correctly I need a reference to the parent Map in the userControl.
This is my XAML:
<m:MapItemsControl x:Name="Pushpinss" ItemsSource="{Binding InventoryItems}">
<m:MapItemsControl.ItemTemplate>
<DataTemplate>
<!-- NORMAL PUSHPIN WORKS -->
<m:Pushpin>
<m:MapLayer.Position>
<m:Location Latitude="{Binding WarehouseLatitude}"
Longitude="{Binding WarehouseLongitude}" />
</m:MapLayer.Position>
</m:Pushpin>
<!-- CUSTOM CONTROL DISPLAYS BUT DOES NOT POSITION CORRECTLY BECAUSE I NEED A REFERENCE TO THE MAP-->
<View:GPSIcon Latitude="{Binding WarehouseLatitude}"
Longitude="{Binding WarehouseLongitude}"
Radius="100000"/>
<x:Arguments>
</x:Arguments>
</DataTemplate>
</m:MapItemsControl.ItemTemplate>
</m:MapItemsControl>
This is my custom control:
public sealed partial class GPSIcon : UserControl
{
private Map _map;
private const double EARTH_RADIUS_METERS = 6378137;
public GPSIcon(Map map)
{
this.InitializeComponent();
_map = map;
_map.ViewChanged += (s, e) =>
{
UpdateAccuracyCircle();
};
}
public static readonly DependencyProperty LatitudeProperty =
DependencyProperty.Register("Latitude", typeof(double), typeof(GPSIcon), new PropertyMetadata(0));
public static readonly DependencyProperty LongitudeProperty =
DependencyProperty.Register("Longitude", typeof(double), typeof(GPSIcon), new PropertyMetadata(0));
public static readonly DependencyProperty RadiusProperty =
DependencyProperty.Register("Radius", typeof(double), typeof(GPSIcon), new PropertyMetadata(0));
public double Latitude
{
get { return (double)GetValue(LatitudeProperty); }
set { SetValue(LatitudeProperty, value); }
}
public double Longitude
{
get { return (double)GetValue(LongitudeProperty); }
set { SetValue(LongitudeProperty, value); }
}
/// <summary>
/// Radius in Metres
/// </summary>
public double Radius
{
get { return (double)GetValue(RadiusProperty); }
set
{
SetValue(RadiusProperty, value);
UpdateAccuracyCircle();
}
}
private void UpdateAccuracyCircle()
{
if (_map != null && Radius >= 0)
{
double groundResolution = Math.Cos(_map.Center.Latitude * Math.PI / 180) * 2 * Math.PI * EARTH_RADIUS_METERS / (256 * Math.Pow(2, _map.ZoomLevel));
double pixelRadius = Radius / groundResolution;
AccuracyCircle.Width = pixelRadius;
AccuracyCircle.Height = pixelRadius;
AccuracyCircle.Margin = new Thickness(-pixelRadius / 2, -pixelRadius / 2, 0, 0);
}
}
}
Is this possible at all? I have also tried using the x:Arguments directive as described here:
http://msdn.microsoft.com/en-us/library/ee795382.aspx
Thanks

Answer 1

UPDATE 1
Do following changes
1) Add empty constructor.
public GPSIcon()
{
this.InitializeComponent();
}
2) Declare DP of type Map
public Map MyMap
{
get { return (Map)GetValue(MyMapProperty); }
set { SetValue(MyMapProperty, value); }
}
public static readonly DependencyProperty MyMapProperty =
DependencyProperty.Register("MyMap", typeof(Map), typeof(GPSIcon), new PropertyMetadata(default(Map), OnMapSet));
private static void OnMapSet(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
_map = ((GPSIcon)(d)).MyMap;
_map.ViewChanged += (ss, ee) =>
{
((GPSIcon)(d)).UpdateAccuracyCircle();
};
}
3) Pass Map object like this in XAML
<m:Map x:Name="objMap">
<m:MapItemsControl x:Name="Pushpinss" ItemsSource="{Binding InventoryItems}">
<m:MapItemsControl.ItemTemplate>
<DataTemplate>
<View:GPSIcon Latitude="{Binding WarehouseLatitude}"
Longitude="{Binding WarehouseLongitude}"
Radius="100000"
MyMap="{Binding ElementName=objMap}"/>
</DataTemplate>
</m:MapItemsControl.ItemTemplate>
</m:MapItemsControl>
</m:Map>
Declare one more dependency property of type Map and then you should pass current map instance as a value of that DP in <View:GPSIcon ... />
Simply, you need to follow the same logic as how to Pass parameter to constructor from xaml in Silverlight

Answer 2

To get your custom UIElement to position properly on the map what you can do instead of doing this in code is simply set the position of the UIElement the same way you set the position of a pushpin.
For example:
<View:GPSIcon Radius="100000">
<m:MapLayer.Position>
<m:Location Latitude="{Binding WarehouseLatitude}"
Longitude="{Binding WarehouseLongitude}" />
</m:MapLayer.Position>
</View:GPSIcon>