我想将复选框列表数据保存在数据库中。我在SQL中创建了一个名为“ tblSubject”的表,并在web.config中创建了连接字符串。但是我仍然得到erorr:
未设置为对象实例的用户代码对象引用未处理NullReferenceException 。
这是c#中的代码:
private void PopulateSubjects()
{
using (SqlConnection conn = new SqlConnection())
{
conn.ConnectionString = ConfigurationManager
.ConnectionStrings["constr"].ConnectionString;
using (SqlCommand cmd = new SqlCommand())
{
cmd.CommandText = "select * from subjects";
cmd.Connection = conn;
conn.Open();
using (SqlDataReader sdr = cmd.ExecuteReader())
{
while (sdr.Read())
{
ListItem item = new ListItem();
item.Text = sdr["Subject"].ToString();
item.Value = sdr["Id"].ToString();
item.Selected = Convert.ToBoolean(sdr["IsSelected"]);
chbox.Items.Add(item);
}
}
conn.Close();
}
}
}
protected void Button1_Click(object sender, EventArgs e)
{
using (SqlConnection conn = new SqlConnection())
{
conn.ConnectionString = ConfigurationManager
.ConnectionStrings["constr"].ConnectionString;
using (SqlCommand cmd = new SqlCommand())
{
cmd.CommandText = "update subjects set IsSelected = @IsSelected" +
" where Id=@Id";
cmd.Connection = conn;
conn.Open();
foreach (ListItem item in chbox.Items)
{
cmd.Parameters.Clear();
cmd.Parameters.AddWithValue("@IsSelected", item.Selected);
cmd.Parameters.AddWithValue("@Id", item.Value);
cmd.ExecuteNonQuery();
}
conn.Close();
}
}
}
并在Web.config中:
<connectionStrings>
<add name=" constr" connectionString="Data Source=(LocalDB)\MSSQLLocalDB;
Initial Catalog = dbtblSubject; Integrated Security = true" providerName="System.Data.SqlClient" />
</connectionStrings>
任何帮助将非常感激。
移除white space
中的Web.config
:
<add name=" constr" ...
到
<add name="constr" ...
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