Essentials: Xamarin.Essentials.NotImplementedInReferenceAssemblyException Android Only

[asfelicetti]

I have implemented Xamarin Essentials in with my forms application (iOS and Droid). iOS is working without issue. Droid is throwing the following error:

This is where the error is thrown.
Geolocation.GetLastKnownLocationAsync().

{Xamarin.Essentials.NotImplementedInReferenceAssemblyException: This functionality is not implemented in the portable version of this assembly. You should reference the NuGet package from your main application project in order to reference the platform-specific…}

The xamarin.essentials nuget reference is in the PCL, iOS, and Droid projects. I have removed and reinstalled all of them, cleaned and rebuilt all projects but the error persists.

[jamesmontemagno]

This most likely means that when you installed it you were not targeting Xamarin.Android 8.1 as your compile target.

Can you uninstall then set your project: https://blog.xamarin.com/android-apps-google-play-target-api-level-requirements/ then install again.

[asfelicetti]

I attempted what you suggested setting min api to 19 and target to 8.1. I also updated xamarin forms to the latest release. The error persists.

I then created a completely new xamarin forms application to rule out my application. I create a one button app that simply calls GeoLocator.GetLocationAsync(). I checked all options for required permissions simply for test purposes. I then ran my app and clicked the button and are getting the following error.

Java.Lang.NullPointerException: Attempt to invoke virtual method 'void android.app.Activity.requestPermissions(java.lang.String[], int)' on a null object reference
at java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.Activity.requestPermissions(java.lang.String[], int)' on a null object reference

It seems like a permissions error but like i stated above I gave the app full permissions.

[jamesmontemagno]

So, you don't have to set the minimum, just your compile version. Minimum can stay at 19.

Looks like perhaps you didn't call the Init in your mainactivity:

https://docs.microsoft.com/en-us/xamarin/essentials/get-started?context=xamarin%2Fxamarin-forms&tabs=windows%2Candroid

[asfelicetti]

@jamesmontemagno Thanks for your assistance, the issue is now resolved per your feedback.

[JoeBGonzalez]

I also received the following error when trying to run DeviceDisplay.ScreenMetrics from my PCL project:
"Unhandled Exception: Xamarin.Essentials.NotImplementedInReferenceAssemblyException: This functionality is not implemented in the portable version of this assembly. You should reference the NuGet package from your main application project in order to reference the platform-specific implementation."
So I thought I would add the following to the MainActivity.cs per the Xamarin.Essentials installation instructions: "Xamarin.Essentials.Platform.Init(this, bundle);" but VS2017 says that Platform does not contain a definition for Init.
I made sure to install Xamarin.Esentials with Compile and target set as v 8.1 (oreo). I have done a clean and rebuild and it didn't help.
I greatly appreciate any help!

[jamesmontemagno]

I would uninstall the nuget and re-install. Ensuring that you have 8.1 set as the compile version.

[JoeBGonzalez]

Thanks James for the fast response! I uninstalled Xamarin.Essentials, confirmed that v8.1 was both the Compile and Target version, and reinstalled Xamarin.Essentials but still got "'Platform' does not contain a definition for 'Init'" at the "Xamarin.Essentials.Platform.Init(this, bundle);". Any thoughts? Thanks again!

[jamesmontemagno]

Can you attach a sample project so I can look?

[JoeBGonzalez]

SyncFusionSample4Support.zip
I worked on a couple of demo projects and I did not run into the issue on either a new Net Standard project or an older PCL project.
I'm only running into the issue in an existing PCL project that is quite big so it will take a little more time for me to make a copy and strip it down until it is small enough to upload it.
In the mean time I am uploading a demo (a reused/modified a previous SyncFusionSample4Support demo) of a PCL project in which I noticed the following two 'smallish' items:
1) the name of the ScreenMetricsChangedEventArgs type and DeviceDisplay.ScreenMetricsChanaged event are misspelled (Chanaged->Changed).
2) the ScreenMetricsChanged event is not being fired when the screen orientation changes. Is it supposed to? I hoping to use the event to detect screen orientation changes.
I will follow up with the demo of the main issue hopefully by tomorrow.
Thanks again James!!

[jamesmontemagno]

Taking a look.

1.) We fixed this in next release 0.9.0-preview (should be soon)
2.) What device?

[jamesmontemagno]

So you code was a bit funky causing issues. You want to do:

        ScreenOrientation currentOrientation = DeviceDisplay.ScreenMetrics.Orientation;
        public Page1()
        {
            InitializeComponent();
            DisplayOrientation(DeviceDisplay.ScreenMetrics.Orientation);
            DeviceDisplay.ScreenMetricsChanaged += OnScreenMetricsChanged;
        }

        void OnScreenMetricsChanged(ScreenMetricsChanagedEventArgs e)  //this event is not being triggered when I change the orientation after launching the app
        {
            // Process changes
            //ScreenOrientation currentOrientation = DeviceDisplay.ScreenMetrics.Orientation;
            var metrics = e.Metrics;




            if (metrics.Orientation != currentOrientation)
            {
                DisplayOrientation(metrics.Orientation);
                currentOrientation = metrics.Orientation;
            }

        }

[JoeBGonzalez]

Cool and thanks again James.
I replaced the code with your changes and it took from 45+ seconds for the OnScreenMetrics event to get triggered when switching from landscape to portrait and 20+ seconds when switching from portrait to landscape.
I am testing on an LG G Pad X 8.0 (aka: LGE LG-V520 in the VS2017 device dropdown).

[JoeBGonzalez]

Sorry James, I take it back! The OnScreenMetrics event is actually being triggered as expected!
It turns out that I was testing through the Visor chrome extension when I was experiencing these delays. I turned off Visor and tried it again and could see that event was being triggered right away! I was surprised to see that Visor was somehow introducing this delay!
Thanks so much for your help!