Simple fix to use CrossCurrentActivity plugin in your .Net Standard based Xamarin.Forms solutions

CrossCurrentActivityHelperExtension.cs

// this goes in your shared .Net Standard project
namespace WhateveryourNamespace.SharedProject.Helpers
{
    /// <summary>
    /// Simple helper extension to access CrossCurrentActivity 
    /// plugin instance from your .NET Standard project.
    /// </summary>
    public static class CrossCurrentActivity
    {
        /// <summary>Current settings to use</summary>
        public static object Current { get; set; }
    }
}

// here's how to configure your Xamarin Android project with it
namespace WhateveryourNamespace.AndroidProject
{
    protected override void OnCreate(Bundle savedInstanceState)
    {
        TabLayoutResource = Resource.Layout.Tabbar;
        ToolbarResource = Resource.Layout.Toolbar;

        base.SetTheme(Resource.Style.MainTheme);
        base.OnCreate(savedInstanceState);

        global::Xamarin.Forms.Forms.Init(this, savedInstanceState);

        Initialize();

        LoadApplication(new App());
    }

    private void Initialize()
    {
        // Init CrossCurrentActivity as usual 
        CrossCurrentActivity.Current.Init(this.Application);
        // Subscribe to the ActivityStateChanged event
        CrossCurrentActivity.Current.ActivityStateChanged += Current_ActivityStateChanged;
    }

    private void Current_ActivityStateChanged(object sender, ActivityEventArgs e)
    {
        // Keep the reference of your Shared project variable in sync
        WhateveryourNamespace.SharedProject.Helpers.CrossCurrentActivity.Current = CrossCurrentActivity.Current.Activity;
    }
}