Getting Started With Reactive Extensions

In this article, we will continue from the previous article and see a few examples around the 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 window 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 the 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 to me. Rather than that, I would prefer to have a 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 a 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.

8 Comments

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Santhakumar Munuswamy11y ago
Good one
Sujeet Suman11y ago
Nice Article.................
Mohammed Ibrahim11y ago
nice
Rakesh11y ago
Good share buddy
Vipul Malhotra11y ago
nice article
Sibeesh Venu11y ago
Nice Share
Mukesh Kumar11y ago
Great, thanks for sharing
Nilesh Jadav11y ago
This is real Great ! Nice work sir !!