列表框选中的文本与列表框文本+自定义文本（richtextbox）

Question

I'm making an application for this website: http://incil.info What I'm trying to make is when a listbox text is selected, it will show it on the richTextBox with the selected text from listbox + custom text.

I'm a bit stuck here..

For now, here is my code:

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 Kutsal_Kitap
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            this.listBox1.SelectedIndexChanged += new System.EventHandler(this.listBox1_SelectedIndexChanged);
        }

        private void btnAra_Click(object sender, EventArgs e)
        {

        }



        private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            richTextBox1.Text = listBox1.SelectedItem.ToString();


        }
    }
    }

This code will only show the selected text from listbox to richtextbox. How do I also add custom text below?

Answer 1

add custom text by conditions

private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
var str =listBox1.SelectedItem.ToString();
if(str=="aaa")
{
        richTextBox1.Text = str + "custom text 1";
}
else if(str=="bbb")
{
        richTextBox1.Text = str + "custom text 2";
}
...


    }