實現效果：

知識運用：

　　StreamReader類的ReadLine方法　　　　//從當前流中讀取一行字元並將資料作為字串返回

　　public override string ReadLine ()

實現程式碼：

        private void button1_Click(object sender, EventArgs e)
        {
            try
            {
                OpenFileDialog open = new OpenFileDialog();
                open.Filter = "文字檔案(*.txt)|*.txt";
                open.ShowDialog();
                textBox1.Text = open.FileName;
                StreamReader sr = new StreamReader(textBox1.Text, Encoding.UTF8);
                label3.Text = sr.ReadLine();
                sr.Close();
            }
            catch (Exception ex)
            { MessageBox.Show(ex.Message); }
        }