Xamarin.Forms ActivityIndicator example - http://forums.xamarin.com/discussion/22309/how-to-show-a-loading-message-in-xamarin-forms-for-all-platforms

App.cs

using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Threading.Tasks;
using Xamarin.Forms;

namespace ActivityIndicatorCase
{
    public class App
    {
        // the static method used as the entry point into your apps
        public static Page GetMainPage()
        {
            // return your actual root page
            // usually this is the point that you wrap it in a NavigationPage
            // but for this example, we're not doing that.
            return new ActivityPage();
        }
    }

    public class ActivityPage : ContentPage
    {
        // this isn't important to the example
        private int _clickCount;

        // constructor of the page
        public ActivityPage()
        {
            // setup your ViewModel
            ViewModel = new ActivityPageViewModel
            {
                ButtonText = "Click Me!"
            };
            // Set the binding context to the newly created ViewModel
            BindingContext = ViewModel;

            // the button is what we're going to use to trigger a long running Async task
            // we're also going to bind the button text so that we can see the binding in action
            var actionButton = new Button();
            actionButton.SetBinding(Button.TextProperty, "ButtonText");
            actionButton.Clicked += async (sender, args) => await SomeLongRunningTaskAsync();

            // here's your activity indicator, it's bound to the IsBusy property of the BaseViewModel
            // those bindings are on both the visibility property as well as the IsRunning property
            var activityIndicator = new ActivityIndicator
            {
                Color = Color.Black,
            };
            activityIndicator.SetBinding(ActivityIndicator.IsVisibleProperty, "IsBusy");
            activityIndicator.SetBinding(ActivityIndicator.IsRunningProperty, "IsBusy");

            // return the layout that includes all the above elements
            Content = new StackLayout
            {
                HorizontalOptions = LayoutOptions.FillAndExpand,
                VerticalOptions = LayoutOptions.FillAndExpand,
                BackgroundColor = Color.White,
                Children = {actionButton, activityIndicator}
            };
        }

        // you need a view model to bind to
        private ActivityPageViewModel ViewModel { get; set; }

        private async Task SomeLongRunningTaskAsync()
        {
            // here's your long running task.
            // set to busy at the start
            ViewModel.IsBusy = true;

            // run your task... and MAKE SURE it's a Task, and NOT on the UI Thread
            await Task.Delay(2500)
                .ContinueWith(task => { _clickCount ++; });

            // finish updating if necessary
            ViewModel.ButtonText = string.Format("I've been clicked {0} times!", _clickCount);

            // make sure you switch the busy indicator back.
            ViewModel.IsBusy = false;
        }
    }

    // all your view models can inherit from the BaseViewModel
    public class ActivityPageViewModel : BaseViewModel
    {
        private string _buttonText;

        public string ButtonText
        {
            get { return _buttonText; }
            set
            {
                _buttonText = value;
                // This is very important. It indicates to the app that you've changed the content of this property
                OnPropertyChanged();
            }
        }
    }

    // Your BaseViewModel MUST inherit from INotifyProprtyChanged.. it's what makes everything work
    public class BaseViewModel : INotifyPropertyChanged
    {
        // here's your shared IsBusy property
        private bool _isBusy;

        public bool IsBusy
        {
            get { return _isBusy; }
            set
            {
                _isBusy = value;
                // again, this is very important
                OnPropertyChanged();
            }
        }

        // this little bit is how we trigger the PropertyChanged notifier.
        public event PropertyChangedEventHandler PropertyChanged;

        public virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
        {
            var handler = PropertyChanged;
            if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

Hi there,
When the activity indicator is on how to disable other controls no the page from interaction?

Thanks.

Hi there,
When the activity indicator is on how to disable other controls no the page from interaction?

Thanks.

Just create a new attribute, ex: "IsEnabled", to work how "IsBusy". And put it in the pages.