<分区>
当我运行我的代码时，它发送了错误，即对象引用未设置为下拉列表 4 中对象的实例。
下拉选择错误
Object reference not set to an instance of an object.
当我从下拉列表中选择项目时
在此先感谢您的帮助
下面是我的代码
protected void LoadOptions4()
{
DropDownList4.Items.Clear();
// DropDownList4 dr = new DropDownList4();
DataTable CardCode = new DataTable();
// string name2;
// string id, name, newName;
SqlConnection connection = new SqlConnection("Data Source=1.2.3.4;Initial Catalog=TestData;Persist Security Info=True;User ID=abcd;Password=abcd12345");
using (connection)
{
// string selected4 = DropDownList3.SelectedItem.Value;
//SqlCommand theCommand = new SqlCommand("SELECT T1.CardCode , T1.CardName, T2.OpprId, T1.CntctPrsn,T2.CprCode,T3.CntctCode,T3.Name FROM OCRD T1 left join OOPR T2 on T1.CardCode=T2.CardCode left join OCPR T3 on T2.CprCode=T3.CntctCode where T1.CardCode=@CardCode ", connection);
SqlCommand theCommand = new SqlCommand("select SlpCode,SlpName from OSLP where SlpCode=@SlpCode and SlpCode<>-1 ", connection);
// SqlDataAdapter adapter = new SqlDataAdapter("SELECT T1.CardCode , T1.CardName, T2.OpprId,T1.CntctPrsn, T2.CprCode,T2.MaxSumLoc FROM OCRD T1 left join OOPR T2 on T1.CardCode=T2.CardCode where T1.CardCode=@selected", connection);
// SqlDataAdapter adapter = new SqlDataAdapter("SELECT T1.CardCode , T1.CardName, T2.OpprId,T1.CntctPrsn, T2.CprCode,T2.MaxSumLoc FROM OCRD T1 left join OOPR T2 on T1.CardCode=T2.CardCode where T1.CardCode=@selected", connection);
string selected5;
selected5 = DropDownList4.SelectedItem.Value;
theCommand.Parameters.AddWithValue("@SlpCode", selected5);
SqlDataAdapter adapter = new SqlDataAdapter(theCommand);
//DataSet ds = new DataSet();
adapter.Fill(CardCode);
//name2 = id;
if (CardCode.Rows.Count > 0)
{
for (int i = 0; i < CardCode.Rows.Count; i++)
{
string name3 = CardCode.Rows[i]["SlpName"].ToString();
string slpCode = CardCode.Rows[i]["SlpCode"].ToString();
// string newName2 = contcode + " ---- " + name2;
DropDownList3.Items.Add(new ListItem(name3, slpCode));
} }}
}