How to use a class create object and call its method in ASP.Net C# example

You need to call the test class in page.aspx by adding

Using _test;  namespace.

and then create an object of class and call the methods using that class.

Refers the simmiller example for your refarence.

test.cs class with namespace _test.

namespace _test
{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Web;

    /// <summary>
    /// Summary description for test
    /// </summary>

    public class test
    {
        public test()
        {
            //
            // TODO: Add constructor logic here
            //
        }

        public string displayName(string message)
        {
            string msg = "HI " + message;
            return msg;
        }

        public int Increament(int i)
        {
            return ++i; 
        }
    }
}

page.aspx Design

  <form id="form1" runat="server">
    <div>
        Enter NAME :
        <asp:TextBox ID="txtname" runat="server"></asp:TextBox>
        <br />
        <br />
        Enter Number :
        <asp:TextBox ID="txtNumber" runat="server"></asp:TextBox>
        <br />
        <br />
        <asp:Button ID="btnsubmit" runat="server" OnClick="Submit" Text="Display" />
        <br />
        <br />
        Name :<asp:Label ID="lblName" runat="server"></asp:Label>
        <br />
        <br />
        Number :
        <asp:Label ID="lblNumber" runat="server"></asp:Label>
    </div>
    </form>

page.aspx.cs

In cs file you need to use _test namespace by adding

using _test;

Also need to create object of test class. then you can call methods or properties of test class using that object.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

using _test;

public partial class page : System.Web.UI.Page
{
    

    protected void Submit(object sender, EventArgs e)
    {
        DisplaynameAndNumber();
    }

    protected void DisplaynameAndNumber()
    {
        test test = new test();
        lblName.Text = test.displayName(txtname.Text);
        lblNumber.Text = test.Increament(Convert.ToInt32(txtNumber.Text)).ToString();
    }
}