Predicate in .NET

Introduction

Today, in this article let's play around with one of the interesting and most useful concept in C#.

Question: What is predicate?

In simple terms "It is delegate which accepts a generic type input and returns a boolean based output".

Step 1: Create a new WebForm project

Step 2: The complete code of WebForm1.aspx looks like this

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm1.aspx.cs" Inherits="PredicateApp.WebForm1" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

</head>

<body>

<div>

<table>

<tr>

<asp:Label ID="Label1" runat="server" Text="Predicate in C#" Font-Bold="true" Font-Size="Large"

Font-Names="Verdana" ForeColor="Maroon"></asp:Label>

</td>

</tr>

<tr>

<td>

<asp:Label ID="Label3" runat="server" Text="Please Enter First Number" Font-Size="Large"

Font-Names="Verdana" Font-Italic="true"></asp:Label>

</td>

<td>

<asp:TextBox ID="TextBox2" runat="server" Width="120px" Height="22px"></asp:TextBox>

</td>

</tr>

<tr>

<td>

<asp:Label ID="Label2" runat="server" Text="Please Enter Second Number" Font-Size="Large"

Font-Names="Verdana" Font-Italic="true"></asp:Label>

</td>

<td>

<asp:TextBox ID="TextBox1" runat="server" Width="120px"></asp:TextBox>

</td>

</tr>

<tr>

<asp:Button ID="Button1" runat="server" Text="Addition" Font-Names="Verdana" Width="213px"

BackColor="Orange" Font-Bold="True" OnClick="Button1_Click" />

</td>

</tr>

<tr>

<asp:Button ID="Button2" runat="server" Text="Substraction" Font-Names="Verdana"

Width="213px" BackColor="Orange" Font-Bold="True" OnClick="Button2_Click" />

</td>

</tr>

<tr>

<asp:Button ID="Button3" runat="server" Text="Multiplication" Font-Names="Verdana"

Width="213px" BackColor="Orange" Font-Bold="True" OnClick="Button3_Click" />

</td>

</tr>

<tr>

<asp:Button ID="Button4" runat="server" Text="Division" Font-Names="Verdana" Width="213px"

BackColor="Orange" Font-Bold="True" OnClick="Button4_Click" />

</td>

</tr>

<tr>

<asp:Label ID="Label5" runat="server" Font-Bold="true" Font-Names="Verdana" ForeColor="Maroon"></asp:Label>

</td>

</tr>

</table>

</div>

</center>

</form>

</body>

</html>

Step 3: The complete code of WebForm1.aspx.cs looks like this

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

namespace PredicateApp

{

public partial class WebForm1 : System.Web.UI.Page

{

protected void Page_Load(object sender, EventArgs e)

{

TextBox2.Focus();

}

protected void Button1_Click(object sender, EventArgs e)

{

if (string.IsNullOrEmpty(TextBox1.Text) || string.IsNullOrEmpty(TextBox2.Text))

{

Label5.Text = "Please Enter Some Values";

Label5.ForeColor = System.Drawing.Color.Red;

}

else

{

double result = +(double.Parse(TextBox2.Text) + double.Parse(TextBox1.Text));

Predicate<double> obj_Add = (double x) => x > 20;

Label5.Text = "Addition Result is Greater Than 20: " + obj_Add(result);

Label5.ForeColor = System.Drawing.Color.Green;

TextBox1.Text = string.Empty;

TextBox2.Text = string.Empty;

}

protected void Button2_Click(object sender, EventArgs e)

{

if (string.IsNullOrEmpty(TextBox1.Text) || string.IsNullOrEmpty(TextBox2.Text))

{

Label5.Text = "Please Enter Some Values";

Label5.ForeColor = System.Drawing.Color.Red;

}

else

{ double result = +(double.Parse(TextBox2.Text) - double.Parse(TextBox1.Text));

Predicate<double> obj_Sub = (double x) => x > 5;

Label5.Text = "Subtraction Result is Greater Than 5: " + obj_Sub(result);

Label5.ForeColor = System.Drawing.Color.Green;

TextBox1.Text = string.Empty;

TextBox2.Text = string.Empty;

}

protected void Button3_Click(object sender, EventArgs e)

{

if (string.IsNullOrEmpty(TextBox1.Text) || string.IsNullOrEmpty(TextBox2.Text))

{

Label5.Text = "Please Enter Some Values";

Label5.ForeColor = System.Drawing.Color.Red;

}

else

{

double result = +(double.Parse(TextBox2.Text) - double.Parse(TextBox1.Text));

Predicate<double> obj_Mul = (double x) => x > 20;

Label5.Text = "Multiplication Result is Greater Than 20: " + obj_Mul(result);

Label5.ForeColor = System.Drawing.Color.Green;

TextBox1.Text = string.Empty;

TextBox2.Text = string.Empty;

}

protected void Button4_Click(object sender, EventArgs e)

{

if (string.IsNullOrEmpty(TextBox1.Text) || string.IsNullOrEmpty(TextBox2.Text))

{

Label5.Text = "Please Enter Some Values";

Label5.ForeColor = System.Drawing.Color.Red;

}

else

{

double result = +(double.Parse(TextBox2.Text) / double.Parse(TextBox1.Text));

Predicate<double> obj_Div = (double x) => x > 2;

Label5.Text = "Division Result is Greater Than 2: " + obj_Div(result);

Label5.ForeColor = System.Drawing.Color.Green;

TextBox1.Text = string.Empty;

TextBox2.Text = string.Empty;

}

Step 4: The output of the application looks like this:

Step 5: The addition result output of the application looks like this: