MonoGame DownloadContentManager

AssetPackContentManager.cs

using System;
using System.IO;
using System.Collections.Generic;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Content;
using Xamarin.Google.Android.Play.Core.AssetPacks;
using Xamarin.Google.Android.Play.Core.AssetPacks.Model;

namespace MonoGameAndroidAds
{
  public class AssetPackContentManager : DownloadContentManager
	{
		IAssetPackManager assetPackManager;
		HashSet<string> assetPacks = new HashSet<string> ();
		Dictionary<string, AssetPackLocation> assetlocationCache = new Dictionary<string, AssetPackLocation> ();
		public AssetPackContentManager (IServiceProvider serviceProvider, IAssetPackManager assetPackManager, string rootDirectory = "Content")
			: base(serviceProvider, rootDirectory)
		{
			this.assetPackManager = assetPackManager;
		}

		public override void RegisterContent (string pack, string location = "")
		{
			if (!assetPacks.Contains (pack))
				assetPacks.Add (pack);
		}

		public override void UnregisterContent (string pack)
		{
			if (assetPacks.Contains (pack))
				assetPacks.Remove (pack);
		}
		protected override Stream OpenStream(string assetName)
		{
			foreach (var pack in assetPacks) {
				string path = GetAbsoluteAssetPath (pack, assetName);
				if (!string.IsNullOrEmpty (path) && File.Exists (path)) {
					MemoryStream memStream = new MemoryStream();
					using (Stream stream = File.Open (path, FileMode.Open)) {
						stream.CopyTo(memStream);
						memStream.Seek(0, SeekOrigin.Begin);
					}
					return memStream;
				}
			}
			// revert back to the normal load process.
			return base.OpenStream (assetName);
		}

		public override (bool result, string state) DownloadContent (string pack)
		{
			var location = assetPackManager.GetPackLocation (pack);
			if (location?.AssetsPath () == null) {
				if (states.ContainsKey (pack))
					return (result:false, state:states[pack]);
				assetPackManager.Fetch (new string[] { pack });
				states[pack] = "downloading";
				return (result:false, state:states[pack]);
			} else {
				return (result:true, state:"complete");
			}
		}

		AssetPackLocation GetPackLocation (string assetPack)
		{
			if (assetlocationCache.ContainsKey (assetPack))
				return assetlocationCache[assetPack];
			var assetPackLocation = assetPackManager.GetPackLocation (assetPack);
			if (assetPackLocation != null)
				assetlocationCache[assetPack] = assetPackLocation;
			return assetPackLocation;
		}

		string GetAbsoluteAssetPath(string assetPack, string relativeAssetPath) {
			AssetPackLocation assetPackPath = GetPackLocation(assetPack);
			if (assetPackPath == null)
				return null;
			string assetsFolderPath = assetPackPath.AssetsPath() ?? null;
			if (assetsFolderPath == null) {
				// asset pack is not ready
				return null;
			}

			string assetPath = Path.Combine(assetsFolderPath, RootDirectory, relativeAssetPath.Replace ("\\", "/") + ".xnb");
			return assetPath;
		}
	}
}

DownloadContentManager.cs

using System;
using System.IO;
using System.Collections.Generic;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Content;
using Xamarin.Google.Android.Play.Core.AssetPacks;
using Xamarin.Google.Android.Play.Core.AssetPacks.Model;

namespace MonoGameAndroidAds
{
	public abstract class DownloadContentManager : ContentManager {

		protected Dictionary<string, string> states = new Dictionary<string, string> ();
		public DownloadContentManager(IServiceProvider serviceProvider, string rootDirectory = "Content")
			: base(serviceProvider, rootDirectory)
		{
			
		}
		public virtual void RegisterContent (string pack, string location = "")
		{
		}
		
		public virtual void UnregisterContent (string pack)
		{
		}

		public virtual bool ContentAvailable (string pack)
		{
			return states.ContainsKey (pack) && states[pack] == "complete";
		}

		public virtual (bool result, string state) DownloadContent (string pack)
		{
			return (result:false, state:"failed");
		}
	}
}