Xamarin Forms - Reference XAML from Android specific .cs file - xaml

Question

I have a page called MapPage.xaml and a code behind called MapPage.xaml.cs. In my android project, I have another file called CustomMapRenderer.cs. In the CustomMapRenderer.cs file, I need to retrieve the item selected variable in a XAML picker found in my MapPage.xaml file, which changes when a user picks an option in my XAML picker.
How to I reference the picker from my CustomMapRenderer.cs?

Answer 1

In the CustomMapRenderer.cs file, I need to retrieve the item selected variable in a XAML picker found in my MapPage.xaml file, which changes when a user picks an option in my XAML picker.
If you followed the official doc Customizing a Map to create your CustomMapRenderer, then in PCL, there should be a class which inherits from Map, for example:
public class CustomMap : Map
{
}
Then, if your picker is another control in your MainPage, you can create a bindable property for your CustomMap, and override OnElementPropertyChanged in your renderer to get this property when it changed.
For example, in PCL:
public class MapWithMyZoomControl : Map
{
public ZoomState MyZoom
{
get { return (ZoomState)GetValue(MyZoomProperty); }
set { SetValue(MyZoomProperty, value); }
}
public static readonly BindableProperty MyZoomProperty =
BindableProperty.Create(
propertyName: "MyZoom",
returnType: typeof(ZoomState),
declaringType: typeof(MapWithMyZoomControl),
defaultValue: ZoomState.normal,
propertyChanged: OnZoomPropertyChanged);
public static void OnZoomPropertyChanged(BindableObject bindable, object oldValue, object newValue)
{
}
public enum ZoomState
{
normal,
zoomin,
zoomout
}
}
And in its renderer:
public class MapWithMyZoomControlRenderer : MapRenderer, IOnMapReadyCallback
{
private GoogleMap map;
public void OnMapReady(GoogleMap googleMap)
{
map = googleMap;
map.UiSettings.ZoomControlsEnabled = false;
}
protected override void OnElementChanged(ElementChangedEventArgs<Map> e)
{
base.OnElementChanged(e);
if (e.OldElement != null)
{
// Unsubscribe
}
if (e.NewElement != null)
{
var formsMap = (MapWithMyZoomControl)e.NewElement;
((MapView)Control).GetMapAsync(this);
}
}
protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
{
base.OnElementPropertyChanged(sender, e);
var element = Element as MapWithMyZoomControl;
if (e.PropertyName == "MyZoom" && map != null)
{
if (element.MyZoom == MapWithMyZoomControl.ZoomState.zoomin)
{
map.AnimateCamera(CameraUpdateFactory.ZoomIn());
}
else if (element.MyZoom == MapWithMyZoomControl.ZoomState.zoomout)
{
map.AnimateCamera(CameraUpdateFactory.ZoomOut());
}
element.MyZoom = MapWithMyZoomControl.ZoomState.normal;
}
}
}
Out of this map control, I use buttons to control to zoom the map:
map.MyZoom = MapWithMyZoomControl.ZoomState.zoomin;
It'a a demo, but you can modify it to make property connected to your picker.