ExecuteScalar错误

Question

我不断收到错误“NullReferenceException未处理。对象引用未设置为对象的实例”第5行

1.    Private void textbox1_TextChanged(object sender,EventArgs e)
2     {
3.       SqlConnection cn=new SqlConnection("Connection string");
4.       String sql ="select name from bank_info where account_no ='"+textbox1.Text+"'";
5.       SqlCommand cmd =new SqlCommand(sql,cn);
6.       Cn.Open();
7.       String s1 = cmd.ExecuteScalar().ToString();
8.       TextBox2.Text =s1.ToString();

我是编程新手。谢谢

Answer 1

这将有助于

 Private void textbox1_TextChanged(object sender,EventArgs e)
 {
   SqlConnection cn=new SqlConnection("Connection string");
   String sql ="select name from bank_info where account_no ='"+textbox1.Text+"'";
   SqlCommand cmd =new SqlCommand(sql,cn);
   Cn.Open();
   Object obj = cmd.ExecuteScalar()
   String s1 = (obj!=null)?(String)obj:"";
   TextBox2.Text =s1.ToString();

Answer 2

你能在dubug模式下看到查询并看到sql。检查在sql中运行相同的查询以查看该帐号是否返回结果。如果没有结果 为了避免异常，你可以检查DB Null，它不会抛出异常。