Çözüldü listBox'a verileri kaydetme

using System.IO;

string path_file = "readfile.txt";

private void Form1_Load(object sender, EventArgs e){
    if (File.Exists (path_file)){
        using (StreamReader sr = new StreamReader(path_file)){
            string row;
            while ((row = sr.ReadLine()) != null){
                listBox1.Items.Add(row);
            }
 
        }
    }
}

private void button1_Click(object sender, EventArgs e){
    listBox1.Items.Add(textBox1.Text.Trim());
}

private void Form1_FormClosing(object sender, FormClosingEventArgs e){
    StreamWriter writer = new StreamWriter(path_file);
    for (int a = 0; a <= listBox1.Items.Count - 1; a++){
        writer.WriteLine(listBox1.Items[a].ToString());
    }
    writer.Close();
}