ListBox not updating SelectedItems

Question

I am writing a code for a school exercise and I have the following code:

private void button1_Click(object sender, EventArgs e)
{
    List<int> lista = new List<int>();
    int delivi = 0;
    int brojac = 0;

    listBox1.BeginUpdate();
    foreach (string s in listBox1.Items)
    {
        int broj = int.Parse(s);
        int delenje_so = int.Parse(textBox1.Text);

        if ((broj % delenje_so) == 0)
        {
            lista.Add(brojac);
            delivi++;
        }

        brojac++;
    }

    for (int i = 0; i < lista.Count; i++)
    {
        //listBox1.SetSelected(lista[i], true);
        MessageBox.Show(lista[i].ToString());
    }
    listBox1.EndUpdate();

    label1.Text = delivi.ToString();
}

Basically, I have a ListBox , Button , TextBox and a Label . I have some items in ListBox and I have to check if those items ( ints ) can be divided by the number in TextBox . Then select all the items that can be divided in the ListBox and output the total amount of numbers that can be divided in the Label .

Everything works in my code, except the fact that ListBox will not select the items that are divided.

I tried updating in the same foreach loop that I do the checking, but I get an error that list has been modified and can't continue. So I made different loop, but nothing happens with it for some reason.

Answer 1

In order to have multiple items selected, you will need to set the listbox's SelectionMode property to MultiSimple or MultiExtended :

The SelectionMode property enables you to determine how many items in the ListBox a user can select at one time …

Answer 2

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace SOFAcrobatics
{
    public partial class Dividers : Form
    {
        public Dividers()
        {
            InitializeComponent();

            this.listBox1.SelectionMode = SelectionMode.MultiSimple;

            for (Int32 i = 1 ; i <= 30 ; i++)
            {
                this.listBox1.Items.Add(i);
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            Int32 n = Int32.Parse(this.textBox1.Text);

            List<Int32> indexes = new List<Int32> ();

            Int32 counter = 0;

            for (Int32 i = 0 ; i < this.listBox1.Items.Count ; i++)
            {
                if ((((Int32)this.listBox1.Items[i]) % n) == 0)
                {
                    indexes.Add(i);
                }
            }

            for (Int32 i = 0 ; i < indexes.Count ; i++)
            {
                this.listBox1.SetSelected(indexes[i], true);
            }

            this.label1.Text = (indexes.Count + 1).ToString();
        }
    }
}