Xamarin.Android MvvmCross Data-Binding Issue - xamarin

Question

I'm trying to create a simple app that uses the Xamarin Geofence plugin. (https://github.com/domaven/xamarin-plugins/tree/master/Geofence).
I'm using MvvmCross for model binding and the App View is interested in events coming from the Geofence instance.
On My ViewModel i have implemented the IGeofenceListener interface so that when any of the events are fired i can directly change the value of the binding properties in my ViewModel that are being targeted in the View.
public class MainViewModel : MvxViewModel, IGeofenceListener
{
double _latitude;
public double Latitude
{
get
{
return _latitude;
}
set
{
_latitude = value;
RaisePropertyChanged(() => Latitude);
}
}
double _longitude;
public double Longitude
{
get
{
return _longitude;
}
set
{
_longitude = value;
RaisePropertyChanged(() => Longitude);
}
}
string _name;
public string Name
{
get
{
return _name;
}
set
{
_name = value;
RaisePropertyChanged(() => Name);
}
}
public void OnAppStarted()
{
Debug.WriteLine(string.Format("{0} - {1}", CrossGeofence.Id, "App started"));
}
public void OnError(string error)
{
Debug.WriteLine(string.Format("{0} - {1}: {2}", CrossGeofence.Id, "Error", error));
}
public void OnLocationChanged(GeofenceLocation location)
{
Longitude = location.Longitude;
Latitude = location.Latitude;
Name = CrossGeofence.Id;
Debug.WriteLine(string.Format("{0} - Long: {1} || Lat: {2}", CrossGeofence.Id, location.Longitude, location.Latitude));
}
public void OnMonitoringStarted(string identifier)
{
Debug.WriteLine(string.Format("{0} - Monitoring started in region: {1}", CrossGeofence.Id, identifier));
}
public void OnMonitoringStopped()
{
Debug.WriteLine(string.Format("{0} - {1}", CrossGeofence.Id, "Monitoring stopped for all regions"));
}
public void OnMonitoringStopped(string identifier)
{
Debug.WriteLine(string.Format("{0} - {1}: {2}", CrossGeofence.Id, "Monitoring stopped in region", identifier));
}
public void OnRegionStateChanged(GeofenceResult result)
{
Longitude = result.Longitude;
Latitude = result.Latitude;
Debug.WriteLine(string.Format("{0} - {1}", CrossGeofence.Id, result.ToString()));
}
}
As you can see, On certain events Im updating the properties of my ViewModel and then calling the RaisePropertyChanged event for the View.
I've added Debug tracing to ensure that these events are actually being fired.
I can see the events firing in my Output window.. and when i debug the application i can see the properties on the ViewModel been updated. It's just that the RaisePropertyChanged event in not actually updating the View.
Here is my View Code :-
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:local="http://schemas.android.com/apk/res-auto"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#00007f"
android:layout_marginTop="10dp">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="20dp"
local:MvxBind="Text Longitude"
android:id="#+id/textViewLongitude"
android:textColor="#android:color/white" />
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="20dp"
local:MvxBind="Text Latitude"
android:id="#+id/textViewLatitude"
android:textColor="#android:color/white" />
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="20dp"
local:MvxBind="Text Name"
android:textColor="#android:color/white"
android:id="#+id/textViewName" />
</LinearLayout>
This is the App setup code in my Core Library :-
public class App : MvxApplication
{
public App()
{
Mvx.RegisterSingleton<IMvxAppStart>(new MvxAppStart<MainViewModel>());
}
}
Here is the Main Activity MvxClass :-
[Activity(Label = "Geofence.Android", MainLauncher = true)]
public class MainActivity : MvxActivity<MainViewModel>
{
protected override void OnViewModelSet()
{
SetContentView(Resource.Layout.Main);
}
protected override void OnCreate(Bundle bundle)
{
base.OnCreate(bundle);
CrossGeofence.Initialize<MainViewModel>();
CrossGeofence.Current.StopMonitoring("LHR");
CrossGeofence.Current.StartMonitoring(new Plugin.Abstractions.GeofenceCircularRegion("Location", 54.9672132, -1.5992939, 2000)
{
NotifyOnStay = true,
NotifyOnEntry = true,
NotifyOnExit = true,
ShowNotification = true,
ShowEntryNotification = false,
ShowExitNotification = false,
ShowStayNotification = true,
NotificationStayMessage = "stay message!",
NotificationEntryMessage = "entry message!",
NotificationExitMessage = "exit message!",
StayedInThresholdDuration = TimeSpan.FromSeconds(1),
});
}
}

Answer 1

This is because CrossGeofence.Initialize<MainViewModel>(); creates a new ViewModel, that is not that one that was created by MvvmCross. You can see that, when you inspect the ViewModel of the activity in the debugger.
Solution
Use the GeofenceListener property.
CrossGeofence.GeofenceListener = (IGeofenceListener)ViewModel;
CrossGeofence.Initialize<MainViewModel>();