Add or remove items to listbox provided no duplicates in c#

Add or remove items to listbox provided no duplicates in c#

Assignment: Below is the code which takes an String input through textbox and it will add that string to listbox. If we tried to insert duplicate item it will generate an error mentioning that item already present. Please do not enter duplicates. One limitation of this project is that the string is case insensitive means, it cannot make a difference between uppercase and lowercase letters. You have to put exact equal string in order to trace the duplicates. I will later will add code which will also have logic for case sensitivity. Thanks.

Here is the Design view:

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.Windows.Forms;

namespace Listbox_add_remove_item_demo

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }

        private void Form1_Load(object sender, EventArgs e)

        {

        }

        private void textBox1_TextChanged(object sender, EventArgs e)

        {

        }

        private void button1_Click(object sender, EventArgs e)

        {

            if (textBox1.Text.Trim() != "")

            {

                if (this.listBox1.Items.Contains(textBox1.Text) == false)

                { 

                listBox1.Items.Add(textBox1.Text);

                textBox1.Text = "";     //textBox1.Clear();

                textBox1.Focus();

                }

                else

                {

                    MessageBox.Show("Alreay contains " + textBox1.Text + " Please avoid duplicate");

                }

            }

            

        }

        private void button2_Click(object sender, EventArgs e)

        {

            int x = listBox1.SelectedIndex;

            if (x != -1)

            {

                listBox1.Items.RemoveAt(x);

            }

            // listBox1.Items.Remove(listBox1.Items[listBox1.SelectedIndex]);

        }

    }

}