Searching in a windows -based application

public partial class Form1 : Form
  {
      int currentIndex = 0;
      public Form1()
      {
          InitializeComponent();
      }
      private void Form1_Load(object sender, EventArgs e)
      {
          this.textBox2.Text = File.ReadAllText(@"F:\TEMP\log.txt");
      }
      private void button2_Click(object sender, EventArgs e)
      {
          this.currentIndex = this.textBox2.Text.IndexOf(this.textBox1.Text, currentIndex+1);
          this.textBox2.Select(this.currentIndex, this.textBox1.Text.Length);
          this.textBox2.Focus();
      }
  }