Let's start by creating a new folder in the FileStorage.Portable project, adding a new file called IMethods.cs, and implementing the following:

public interface IMethods 
  {
    #region Methods
    void Exit();
    void DisplayEntryAlert(TaskCompletionSource<string> tcs, string message);
    #endregion 
  }

For all native projects, add a new folder called Extras. Let's start with the iOS project. add a new file called IOSMethods.cs, and implement the following:

public class IOSMethods : IMethods
  {
    #region Public Methods
    public void Exit()
     {
       UIApplication.SharedApplication.PerformSelector(new ObjCRuntime.Selector("terminateWithSuccess"), null, 0f);
     }
    public void DisplayEntryAlert(TaskCompletionSource<string> tcs, string message)
    { 
      UIAlertView alert = new UIAlertView(); alert.Title = "Title"; 
      alert.AddButton("OK");
      alert.AddButton("Cancel"); 
      alert.Message = message;
      alert.AlertViewStyle...