简单问题，求指教！datagridviw删除和修改的两个问题！

Question

问题1：当我点击删除那个button时，结果总是显示的删除失败，为什么啊？大家帮忙改改吧
以下是我的代码：
 private void btndel_Click(object sender, EventArgs e)
        {
            string bno =BookInfo.CurrentRow.Cells[0].Value.ToString();
            string connStr = @"Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\bookmanage.mdf;Integrated Security=True;User Instance=True";
            SqlConnection conn = new SqlConnection(connStr);
            string sql = String.Format("delete from bkinfo where Bno='"+bno+"'");
            try
            {
                conn.Open();
                SqlCommand cmd = new SqlCommand(sql, conn);
                cmd.ExecuteNonQuery();
                int count = cmd.ExecuteNonQuery();
                if (count > 0)
                {
                    MessageBox.Show("删除图书成功", "删除成功", MessageBoxButtons.OK, MessageBoxIcon.Information);
                }
                else
                {
                    MessageBox.Show("删除图书失败", "删除失败", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
                }            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message, "操作数据库出错!", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
            }
            finally
            {
                conn.Close();
            }
        }
问题2：点击修改后，错位地方为：dataAdapter.Update(dataSet,"bkinfo");
报错为“未将对象引用设置到对象的实例”。该怎么修改？
以下是我整个窗体的代码：
public partial class BookAlter : Form
    {
        SqlDataAdapter dataAdapter;        DataSet dataSet;
        public BookAlter()
        {
            InitializeComponent();
        }        private void btnlook_Click(object sender, EventArgs e)
        {
            string bookname = txtName.Text;
            string connStr = @"Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\bookmanage.mdf;Integrated Security=True;User Instance=True";
            SqlConnection conn = new SqlConnection(connStr);
            string sql = String.Format("select * from bkinfo where Bname like'%{0}%'", bookname);
            try
            {
                SqlDataAdapter dataAdapter = new SqlDataAdapter(sql, conn);
                DataSet dataSet = new DataSet("Bkinfo");
                dataAdapter.Fill(dataSet);
                BookInfo.Columns[0].DataPropertyName = "Bno";
                BookInfo.Columns[1].DataPropertyName = "Bname";
                BookInfo.Columns[2].DataPropertyName = "Writer";
                BookInfo.Columns[3].DataPropertyName = "Btype";
                BookInfo.Columns[4].DataPropertyName = "Bpress";
                BookInfo.Columns[5].DataPropertyName = "Bnumber";
                BookInfo.Columns[6].DataPropertyName = "Bprice";
                BookInfo.DataSource = dataSet.Tables[0];//[0]代表数据集的第一个表
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message, "操作数据库出错", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
            }
        }        private void btnalter_Click(object sender, EventArgs e)
        {
              SqlCommandBuilder builder=new SqlCommandBuilder(dataAdapter);            dataAdapter.Update(dataSet,"bkinfo");
        }        private void btnout_Click(object sender, EventArgs e)
        {
            this.Close();
        }
        }
    }

Answer 1

  string sql = String.Format("delete bkinfo where Bno='"+bno+"'");

Answer 2

dataAdapter 和 dataSet  没有实例化

Answer 3

我试着实例化后，又出现问题了，Update 无法找到 TableMapping['bkinfo'] 或 DataTable“bkinfo”。

Answer 4

 SqlCommand cmd = new SqlCommand(sql, conn);
                cmd.ExecuteNonQuery(); 这句话去掉
                int count = cmd.ExecuteNonQuery();

Answer 5

  private void btnalter_Click(object sender, EventArgs e)
        {
          string connStr = @"DataSource=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\bookmanage.mdf;Integrated Security=True;User Instance=True";
            SqlConnection conn = new SqlConnection(connStr);
            string sql ="select * from bkinfo";
           
              SqlDataAdapter dataAdapter = new SqlDataAdapter(sql, conn);
              DataSet dataSet = new DataSet("Bkinfo");
              dataAdapter.Fill(dataSet);
              SqlCommandBuilder builder=new SqlCommandBuilder(dataAdapter);              dataAdapter.Update(dataSet,"bkinfo");
        }