Port of SSSnackbar https://github.com/stonesam92/SSSnackbar

Snackbar.cs

public sealed class Snackbar : UIView
{
    public TimeSpan Duration { get; set; }
    public Action<Snackbar> OnAction { get; set; }
    public Action<Snackbar> OnDismiss { get; set; }
    private static Snackbar _currentlyVisibleSnackbar;
    private readonly UILabel _messageLabel;
    private readonly UIButton _actionButton;
    private readonly UIView _separator;
    private NSLayoutConstraint[] _horizontalLayoutConstraints;
    private NSLayoutConstraint[] _visibleVerticalLayoutConstraints;
    private NSLayoutConstraint[] _hiddenVerticalLayoutConstraints;
    private NSTimer _dismissalTimer;
    private bool _actionDispatched;

    public static Snackbar WithMessage(string message, string actionText, TimeSpan duration,
        Action<Snackbar> onAction, Action<Snackbar> onDismiss)
    {
        var snackBar = new Snackbar(message, actionText, duration, onAction, onDismiss);
        return snackBar;
    }

    private Snackbar(string message, string actionText, TimeSpan duration,
        Action<Snackbar> onAction, Action<Snackbar> onDismiss) : base(new CGRect(0,0,0,0))
    {
        TranslatesAutoresizingMaskIntoConstraints = false;

        Duration = duration;
        OnAction = onAction;
        OnDismiss = onDismiss;


        _messageLabel = new UILabel {
            Text = message,
            TranslatesAutoresizingMaskIntoConstraints = false,
            Font = UIFont.SystemFontOfSize(14f),
            TextColor = UIColor.White
        };
        _messageLabel.SizeToFit();

        _actionButton = new UIButton(UIButtonType.System) {
            TranslatesAutoresizingMaskIntoConstraints = false
        };
        _actionButton.TitleLabel.Font = UIFont.SystemFontOfSize(14f, UIFontWeight.Bold);
        _actionButton.SetTitle(actionText, UIControlState.Normal);
        _actionButton.SetTitleColor(UIColor.White, UIControlState.Normal);
        _actionButton.SizeToFit();
        _actionButton.TouchUpInside += ExecuteAction;

        _separator = new UIView {
            BackgroundColor = UIColor.FromWhiteAlpha(0.99f, 0.1f),
            TranslatesAutoresizingMaskIntoConstraints = false
        };

        AddSubview(_messageLabel);
        AddSubview(_actionButton);
        AddSubview(_separator);

        Opaque = false;
    }

    public override void Draw(CGRect rect)
    {
        base.Draw(rect);

        using (var context = UIGraphics.GetCurrentContext())
        {
            context.SaveState();

            UIColor.FromWhiteAlpha(0.1f, 0.9f).SetFill();
            var clippath = UIBezierPath.FromRoundedRect(rect, 3f);
            clippath.Fill();

            context.RestoreState();
        }
    }

    public void Show()
    {
        var topController = UIApplication.SharedApplication.KeyWindow.RootViewController;
        while (topController?.PresentedViewController != null) {
            topController = topController?.PresentedViewController;
        }

        if (topController == null)
        {
            Console.WriteLine("I have no top controller, I am drunk...");
            return;
        }

        var superView = topController.View;
        var shouldReplaceExistingSnackbar = _currentlyVisibleSnackbar != null;

        if (shouldReplaceExistingSnackbar)
        {
            _currentlyVisibleSnackbar.InvalidateTimer();
            _currentlyVisibleSnackbar.Dismiss(false);
        }

        superView.AddSubview(this);
        superView.AddConstraints(HorizontalLayoutConstraints);
        superView.AddConstraints(shouldReplaceExistingSnackbar
            ? VisibleVerticalLayoutConstraints
            : HiddenVerticalLayoutConstraints);
        superView.LayoutIfNeeded();
        SetupContentLayout();

        if (!shouldReplaceExistingSnackbar)
        {
            superView.RemoveConstraints(HiddenVerticalLayoutConstraints);
            superView.AddConstraints(VisibleVerticalLayoutConstraints);

            Animate(0.2, 0, UIViewAnimationOptions.CurveEaseOut,
                () => superView.LayoutIfNeeded(), () => { });
        }

        _dismissalTimer = NSTimer.CreateScheduledTimer(Duration, TimeoutForDismissal);

        _currentlyVisibleSnackbar = this;
    }

    private void TimeoutForDismissal(NSTimer nsTimer)
    {
        Dismiss();
    }

    private void Dismiss(bool animated = true)
    {
        InvalidateTimer();
        Superview.RemoveConstraints(VisibleVerticalLayoutConstraints);
        Superview.AddConstraints(HiddenVerticalLayoutConstraints);
        _currentlyVisibleSnackbar = null;

        if (!animated)
        {
            ExecuteDismissal();
            RemoveFromSuperview();
        }
        else
        {
            Animate(0.2, 0, UIViewAnimationOptions.CurveEaseIn,
                () => Superview.LayoutIfNeeded(),
                () => {
                    if (!_actionDispatched)
                        ExecuteDismissal();
                    RemoveFromSuperview();
                });
        }
    }

    private void InvalidateTimer()
    {
        _dismissalTimer?.Invalidate();
        _dismissalTimer?.Dispose();
        _dismissalTimer = null;
    }

    private void SetupContentLayout()
    {
        var constraints = new List<NSLayoutConstraint>();

        constraints.AddRange(
            NSLayoutConstraint.FromVisualFormat(
                "|-8-[label]-(>=8)-[sep(1)]-8-[button]-8-|",
                NSLayoutFormatOptions.AlignAllCenterY,
                "label", _messageLabel, "button", _actionButton, "sep", _separator));

        constraints.AddRange(
            NSLayoutConstraint.FromVisualFormat(
                "V:|-0-[sep]-0-|", 0, "sep", _separator));

        constraints.Add(NSLayoutConstraint.Create(_messageLabel, NSLayoutAttribute.CenterY,
            NSLayoutRelation.Equal, this, NSLayoutAttribute.CenterY, 1, 0));

        AddConstraints(constraints.ToArray());
        LayoutIfNeeded();
    }

    private NSLayoutConstraint[] HorizontalLayoutConstraints =>
        _horizontalLayoutConstraints ?? (_horizontalLayoutConstraints =
            NSLayoutConstraint.FromVisualFormat(@"H:|-5-[bar]-(5)-|", 0, "bar", this));

    private NSLayoutConstraint[] VisibleVerticalLayoutConstraints =>
        _visibleVerticalLayoutConstraints ?? (_visibleVerticalLayoutConstraints =
            NSLayoutConstraint.FromVisualFormat(@"V:[bar(44)]-(5)-|", 0, "bar", this));

    private NSLayoutConstraint[] HiddenVerticalLayoutConstraints =>
        _hiddenVerticalLayoutConstraints ?? (_hiddenVerticalLayoutConstraints =
            NSLayoutConstraint.FromVisualFormat(@"V:[bar(44)]-(-50)-|", 0, "bar", this));

    private void ExecuteAction(object sender, EventArgs eventArgs)
    {
        InvalidateTimer();



        ExecuteAction();
        Dismiss();
    }

    private void ExecuteAction()
    {
        _actionDispatched = true;
        OnAction?.Invoke(this);
    }

    private void ExecuteDismissal()
    {
        if (!_actionDispatched)
            OnDismiss?.Invoke(this);
    }
}