Add project files.

Assets/AboutAssets.txt

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+Any raw assets you want to be deployed with your application can be placed in
+this directory (and child directories) and given a Build Action of "AndroidAsset".
+
+These files will be deployed with your package and will be accessible using Android's
+AssetManager, like this:
+
+public class ReadAsset : Activity
+{
+    protected override void OnCreate (Bundle bundle)
+    {
+        base.OnCreate (bundle);
+
+        InputStream input = Assets.Open ("my_asset.txt");
+    }
+}
+
+Additionally, some Android functions will automatically load asset files:
+
+Typeface tf = Typeface.CreateFromAsset (Context.Assets, "fonts/samplefont.ttf");

MainActivity.cs

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+using System;
+using System.Linq;
+using Android.App;
+using Android.Content;
+using Android.OS;
+using Android.Runtime;
+using Android.Support.Design.Widget;
+using Android.Support.V7.App;
+using Android.Views;
+using Android.Widget;
+
+namespace YoutubeDL {
+	[Activity(Label = "@string/app_name", Theme = "@style/AppTheme.NoActionBar", MainLauncher = true)]
+	[IntentFilter(
+		new[] { Android.Content.Intent.ActionSend },
+		Categories = new[] { Android.Content.Intent.CategoryDefault },
+		DataHosts = new[] { "youtube.com", "youtu.be" },
+		DataMimeType = "text/plain")]
+	public class MainActivity : AppCompatActivity {
+		protected override void OnCreate(Bundle savedInstanceState) {
+			base.OnCreate(savedInstanceState);
+			Xamarin.Essentials.Platform.Init(this, savedInstanceState);
+			SetContentView(Resource.Layout.activity_main);
+
+			Android.Support.V7.Widget.Toolbar toolbar = FindViewById<Android.Support.V7.Widget.Toolbar>(Resource.Id.toolbar);
+			SetSupportActionBar(toolbar);
+
+			FloatingActionButton fab = FindViewById<FloatingActionButton>(Resource.Id.fab);
+			fab.Click += FabOnClick;
+
+			if (Intent?.Extras != null) {
+				string youtubeUrl = Intent.GetStringExtra(Intent.ExtraText);
+			}
+		}
+
+		public override bool OnCreateOptionsMenu(IMenu menu) {
+			MenuInflater.Inflate(Resource.Menu.menu_main, menu);
+			return true;
+		}
+
+		public override bool OnOptionsItemSelected(IMenuItem item) {
+			int id = item.ItemId;
+			if (id == Resource.Id.action_settings) {
+				return true;
+			}
+
+			return base.OnOptionsItemSelected(item);
+		}
+
+		private void FabOnClick(object sender, EventArgs eventArgs) {
+			View view = (View) sender;
+			Snackbar.Make(view, "Replace with your own action", Snackbar.LengthLong)
+				.SetAction("Action", (Android.Views.View.IOnClickListener) null).Show();
+		}
+
+		public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Android.Content.PM.Permission[] grantResults) {
+			Xamarin.Essentials.Platform.OnRequestPermissionsResult(requestCode, permissions, grantResults);
+
+			base.OnRequestPermissionsResult(requestCode, permissions, grantResults);
+		}
+	}
+}
+

Properties/AndroidManifest.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
+          android:versionCode="1" 
+          android:versionName="1.0" 
+          package="com.companyname.youtubedl">
+  <uses-sdk android:minSdkVersion="24" android:targetSdkVersion="28" />
+  <application android:allowBackup="true" android:icon="@mipmap/ic_launcher" android:label="@string/app_name" android:roundIcon="@mipmap/ic_launcher_round" android:supportsRtl="true" android:theme="@style/AppTheme">
+  </application>
+  <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
+</manifest>

Properties/AssemblyInfo.cs

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+using System.Reflection;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using Android.App;
+
+// General Information about an assembly is controlled through the following 
+// set of attributes. Change these attribute values to modify the information
+// associated with an assembly.
+[assembly: AssemblyTitle("YoutubeDL")]
+[assembly: AssemblyDescription("")]
+[assembly: AssemblyConfiguration("")]
+[assembly: AssemblyCompany("")]
+[assembly: AssemblyProduct("YoutubeDL")]
+[assembly: AssemblyCopyright("Copyright ©  2018")]
+[assembly: AssemblyTrademark("")]
+[assembly: AssemblyCulture("")]
+[assembly: ComVisible(false)]
+
+// Version information for an assembly consists of the following four values:
+//
+//      Major Version
+//      Minor Version 
+//      Build Number
+//      Revision
+[assembly: AssemblyVersion("1.0.0.0")]
+[assembly: AssemblyFileVersion("1.0.0.0")]

Resources/AboutResources.txt

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+Images, layout descriptions, binary blobs and string dictionaries can be included 
+in your application as resource files.  Various Android APIs are designed to 
+operate on the resource IDs instead of dealing with images, strings or binary blobs 
+directly.
+
+For example, a sample Android app that contains a user interface layout (main.xml),
+an internationalization string table (strings.xml) and some icons (drawable-XXX/icon.png) 
+would keep its resources in the "Resources" directory of the application:
+
+Resources/
+    drawable/
+        icon.png
+
+    layout/
+        main.xml
+
+    values/
+        strings.xml
+
+In order to get the build system to recognize Android resources, set the build action to
+"AndroidResource".  The native Android APIs do not operate directly with filenames, but 
+instead operate on resource IDs.  When you compile an Android application that uses resources, 
+the build system will package the resources for distribution and generate a class called "R" 
+(this is an Android convention) that contains the tokens for each one of the resources 
+included. For example, for the above Resources layout, this is what the R class would expose:
+
+public class R {
+    public class drawable {
+        public const int icon = 0x123;
+    }
+
+    public class layout {
+        public const int main = 0x456;
+    }
+
+    public class strings {
+        public const int first_string = 0xabc;
+        public const int second_string = 0xbcd;
+    }
+}
+
+You would then use R.drawable.icon to reference the drawable/icon.png file, or R.layout.main 
+to reference the layout/main.xml file, or R.strings.first_string to reference the first 
+string in the dictionary file values/strings.xml.