[英]Bring data into DropDownList from SQL in ASP.NET / C#?
嗨,我是C#的新手,我的技能還很不足,我希望將SQL表中的數據導入表中的'asp:DropDownList'中。
我收到此錯誤: System.NullReferenceException:對象引用未設置為object的實例 。
前端html看起來像這樣:
<asp:Table ID="Table1" runat="server" Font-Size="Medium" Width="960" BorderWidth="3" CellPadding="5" CellSpacing="5" CssClass="table table-bordered table-striped table-hover table-condensed table-responsive">
<asp:TableHeaderRow runat="server" Font-Bold="true">
<asp:TableHeaderCell Width="20%">Activity</asp:TableHeaderCell>
<asp:TableHeaderCell>Hazards</asp:TableHeaderCell>
<asp:TableHeaderCell Width="15%">Risk Level</asp:TableHeaderCell>
</asp:TableHeaderRow>
<asp:TableRow ID="TableRow1" runat="server" >
<asp:TableCell>Camping</asp:TableCell>
<asp:TableCell>Emergency evacuation</asp:TableCell>
<asp:TableCell><asp:DropDownList ID="ddl1" runat="server"></asp:DropDownList></asp:TableCell>
</asp:TableRow>
</asp:Table>
</div>
我簡要介紹過的C#代碼是這樣的:
public partial class _Default : Page
{
protected void Page_Load(object sender, EventArgs e)
{
if (!string.IsNullOrEmpty((string)Session["TripCode"]))
{
txtTripCode.Text = (string)Session["TripCode"];
}
else
{
txtTripCode.Text = "NOT PROVIDED";
}
if (!string.IsNullOrEmpty((string)Session["TripOrg"]))
{
txtTripOrg.Text = (string)Session["TripOrg"];
}
else
{
txtTripOrg.Text = "ERROR: NO DATA PROVIDED";
}
if (!string.IsNullOrEmpty((string)Session["TripDesc"]))
{
txtTripDesc.Text = (string)Session["TripDesc"];
}
else
{
txtTripDesc.Text = "ERROR: NO DATA PROVIDED";
}
if (!this.IsPostBack)
{
string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
using (SqlConnection con = new SqlConnection(constr))
{
using (SqlCommand cmd = new SqlCommand("SELECT TOP 1000 [MainActivityID],[ID],[Activity],[Hazards],[Risk_Level],[Controls] FROM [STRIDES_SQL].[dbo].[STRIDES_RA_Activities]"))
{
cmd.CommandType = CommandType.Text;
cmd.Connection = con;
con.Open();
ddl1.DataSource = cmd.ExecuteReader();
ddl1.DataTextField = "Name";
ddl1.DataValueField = "MainActivityID";
ddl1.DataBind();
con.Close();
}
}
ddl1.Items.Insert(0, new ListItem("--Select Customer--", "0"));
}
}
有什么辦法可以阻止這種情況的發生?
感謝您的幫助或諒解,在此先感謝任何人!
檢查您的web.config以便在“配置-> ConnectionStrings”部分中進行構建。 如果不存在,請添加連接字符串。
檢查https://www.connectionstrings.com/以獲取正確的語法。
還行
ddl1.DataTextField = "Name";
會給你下一個錯誤。 名稱字段不是查詢的一部分。
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