Handle execution on main thread in Xamarin projects

MainQueue.cs

using Xamarin.Forms;

namespace System.Threading.Tasks {
	public static class MainQueue {
		static int mainThreadId = int.MinValue;

		public static void Init() {
			Init(Environment.CurrentManagedThreadId);
		}

		public static void Init(int mainThreadId) {
			if (MainQueue.mainThreadId != int.MinValue) throw new NotSupportedException("you may call Init() only once");
			MainQueue.mainThreadId = mainThreadId;
		}

		public static bool IsOnMain {
			get { 
				if (mainThreadId == int.MinValue) throw new NotSupportedException("you have to call Init() first");
				return Environment.CurrentManagedThreadId == mainThreadId;
			}
		}

		static void EnsureInvokeOnMainThread(Action action) {
			if (IsOnMain) {
				action();
			} else {
				Device.BeginInvokeOnMainThread(action);
			}
		}

		public static Task Queue(Action action) {
			var tcs = new TaskCompletionSource<object>();
			Device.BeginInvokeOnMainThread(() => {
				try {
					action?.Invoke();
					tcs.SetResult(null);
				} catch (Exception ex) {
					tcs.SetException(ex);
				}
			});
			return tcs.Task;   
		}

		public static Task Run(Action action) {
			var tcs = new TaskCompletionSource<object>();
			EnsureInvokeOnMainThread(() => {
				try {
					action?.Invoke();
					tcs.SetResult(null);
				} catch (Exception ex) {
					tcs.SetException(ex);
				}
			});
			return tcs.Task;    
		}
	}
}