Getting Started With Reactive Extensions - Part 2

In this article, we will continue from the previous article and see few examples around UI side. Let us suppose the following snippet, wherein I have simply created one windows form and attached a textbox to it.

using System;
using System.Reactive.Linq;
using System.Windows.Forms;

namespace ReactiveExtensions
{
    internal class Program
    {
        private static void Main(string[] args)
        {
           // ObservableGetValue();
            var textbox = new TextBox();
            var form = new Form
            {
                Controls = {textbox}
            };

          Application.Run(form);
        }


        private static void ObservableGetValue()
        {
            IObservable<string> obj = Observable.Generate(
                0, //Sets the initial value like for loop
                _ => true, //Don't stop till i say so, infinite loop
                i => i + 1, //Increment the counter by 1 everytime
                i => new string('#', i), //Append #
                i => TimeSelector(i)); //delegated this to private method which just calculates time

            //Subscribe here
            using (obj.Subscribe(Console.WriteLine))
            {
                Console.WriteLine("Press any key to exit!!!");
                Console.ReadLine();
            }
        }

        //Returns TimeSelector
        private static TimeSpan TimeSelector(int i)
        {
            return TimeSpan.FromSeconds(i);
        }
    }
}

Now, with the above change in place, it will simply give me one windows form with one text-box in it.



Now, I would like to listen to text changed event. So, what I would do? I will simply go ahead and attach text changed handler as in the following code snippet.



Therefore, it has created the following sample event code.

using System;
using System.Reactive.Linq;
using System.Windows.Forms;

namespace ReactiveExtensions
{
    internal class Program
    {
        private static void Main(string[] args)
        {
           // ObservableGetValue();
            var textbox = new TextBox();
            var form = new Form
            {
                Controls = {textbox}
            };

            //Trying to fetch the value from textbox
            textbox.TextChanged += textbox_TextChanged;

          Application.Run(form);
        }

        static void textbox_TextChanged(object sender, EventArgs e)
        {
            throw new NotImplementedException();
        }


        private static void ObservableGetValue()
        {
            IObservable<string> obj = Observable.Generate(
                0, //Sets the initial value like for loop
                _ => true, //Don't stop till i say so, infinite loop
                i => i + 1, //Increment the counter by 1 everytime
                i => new string('#', i), //Append #
                i => TimeSelector(i)); //delegated this to private method which just calculates time

            //Subscribe here
            using (obj.Subscribe(Console.WriteLine))
            {
                Console.WriteLine("Press any key to exit!!!");
                Console.ReadLine();
            }
        }

        //Returns TimeSelector
        private static TimeSpan TimeSelector(int i)
        {
            return TimeSpan.FromSeconds(i);
        }
    }
}

But, if you look at the following screenshot, textchanged is not available.



Hence, this won't be helpful for me. Rather than that, I would prefer to have reactive extension and subscribe the same as shown below.

private static void Main(string[] args)
{
   // ObservableGetValue();
    var textbox = new TextBox();
    var form = new Form
    {
        Controls = {textbox}
    };

    //Using Rx, to get the textchanged

    var textChanged = Observable.FromEventPattern<EventArgs>(textbox, "TextChanged");

    //then, I will subscribe the same

  Application.Run(form);
}

Now, if you see the following screenshot, it gave me EventArgs.





Here, in order to get changed text, I need to make use of LINQ on the top of Rx. Hence, below is the finished code for the same. I have done little bit of refactoring as well, just to keep the code more readable and clean.

using System;
using System.Reactive.Linq;
using System.Windows.Forms;

namespace ReactiveExtensions
{
    internal class Program
    {
        private static void Main(string[] args)
        {
            // ObservableGetValue();
            GetTextBoxValue();
        }

        private static void GetTextBoxValue()
        {
            var textbox = new TextBox();
            var form = new Form
            {
                Controls = {textbox}
            };

            //Using Rx, to get the textchanged

            var textChanged = Observable.FromEventPattern<EventArgs>(textbox, "TextChanged");

            //then, I will subscribe the same using LINQ Projection

            var query = from e in textChanged
                select ((TextBox) e.Sender).Text;

            //Hence, if the application quits, i want to unsubscribe
            using (query.Subscribe(Console.WriteLine))
            {
                Application.Run(form);
            }
        }


        private static void ObservableGetValue()
        {
            IObservable<string> obj = Observable.Generate(
                0, //Sets the initial value like for loop
                _ => true, //Don't stop till i say so, infinite loop
                i => i + 1, //Increment the counter by 1 everytime
                i => new string('#', i), //Append #
                i => TimeSelector(i)); //delegated this to private method which just calculates time

            //Subscribe here
            using (obj.Subscribe(Console.WriteLine))
            {
                Console.WriteLine("Press any key to exit!!!");
                Console.ReadLine();
            }
        }

        //Returns TimeSelector
        private static TimeSpan TimeSelector(int i)
        {
            return TimeSpan.FromSeconds(i);
        }
    }
}

Hence, with the above change in place, when I run the app, it will give us the following output.



You can also download the source code from here.

With this I would like to wrap this session here. Thanks for joining me.