Untitled

using System;
using System.IO;
using System.Windows.Forms;

namespace WindowsFormsApp29
{
    public partial class Form1 : Form
    {
        String Data;
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_DragDrop(object sender, DragEventArgs e)
        {
            string[] veriler = (string[])e.Data.GetData(DataFormats.FileDrop, false);
            StreamReader reader = new StreamReader(veriler[0]);
            Data = reader.ReadToEnd();
        }

        private void Form1_DragEnter(object sender, DragEventArgs e)
        {
            if (e.Data.GetDataPresent(DataFormats.FileDrop))
                e.Effect = DragDropEffects.All;
            else 
                e.Effect = DragDropEffects.None;
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            Data = null;
            lst_cities.Items.Add("İstanbul");
            lst_cities.Items.Add("Kocaeli");
            lst_cities.Items.Add("Artvin");
            lst_cities.SelectionMode = SelectionMode.MultiExtended;
        }

        private void btn_search_Click(object sender, EventArgs e)
        {
            string key = tb_search.Text;

            MessageBox.Show("Aranan : '" + key + "' " +(Data.Contains(key) ? "Mevcut!" : "Mevcut değil!"));
        }

        private void btn_rakamsayisi_Click(object sender, EventArgs e)
        {
            String num = tb_rakam.Text;
            int digit = Convert.ToInt32(num);
            int count = 0;

            if (digit > 10 || digit < 0)
            {
                MessageBox.Show("Lütfen rakam giriniz");
                return;
            }
            count = 0;
            char digitChar = (char)('0' + digit);
            foreach (char c in Data)
                if (c == digitChar)
                    count++;
            MessageBox.Show("Aranan Rakam: '" + digit + "' " + count + " kadar bulunuyor!");
        }

        private void btn_fetch_Click(object sender, EventArgs e)
        {
            for (int i = 0; i < lst_cities.Items.Count; i++)
            {
                var item = lst_cities.Items[i];

                if (Data.Contains(item.ToString()))
                    lst_cities.SetSelected(i, true);
            }
        }
    }
}