private void button4_Click(object sender, EventArgs e)
{
listBox1.Items.Clear();
Searcher isearcher = new Searcher(_indexTarget);
string [] docs = isearcher.SearchDocs(textBox2.Text);
label1.Text = docs.Length.ToString() + " hit(s).";
listBox1.Items.AddRange(docs);
isearcher.Close();
}