Cannot have multiple items selected in a DropDownList but debugger steps through code perfectly
The subject error appears when I refresh the page (databinding is done on page load). Stepping through the page's code reveals no errors and no page is referenced in the stack trace:
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.Web.HttpException: Cannot have multiple items selected in a DropDownList.
Source Error:
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.
Stack Trace:
[HttpException (0x80004005): Cannot have multiple items selected in a DropDownList.]
System.Web.UI.WebControls.DropDownList.VerifyMultiSelect() +106
System.Web.UI.WebControls.ListControl.RenderContents(HtmlTextWriter writer) +161
System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter writer) +32
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +27
System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +208
System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
System.Web.UI.WebControls.WebControl.RenderContents(HtmlTextWriter writer) +10
System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter writer) +32
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +27
System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +208
System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
System.Web.UI.Control.Render(HtmlTextWriter writer) +10
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +27
System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +208
System.Web.UI.UpdatePanel.RenderChildren(HtmlTextWriter writer) +256
System.Web.UI.UpdatePanel.Render(HtmlTextWriter writer) +37
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +27
System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +208
System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
System.Web.UI.Control.Render(HtmlTextWriter writer) +10
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +27
System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +208
System.Web.UI.HtmlControls.HtmlForm.RenderChildren(HtmlTextWriter writer) +173
System.Web.UI.HtmlControls.HtmlContainerControl.Render(HtmlTextWriter writer) +31
System.Web.UI.HtmlControls.HtmlForm.Render(HtmlTextWriter output) +53
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +27
System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
System.Web.UI.HtmlControls.HtmlForm.RenderControl(HtmlTextWriter writer) +40
System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +208
System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
System.Web.UI.Control.Render(HtmlTextWriter writer) +10
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +27
System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +208
System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
System.Web.UI.Page.Render(HtmlTextWriter writer) +29
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +27
System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3060
When last this happened, I had this image tag on the master page:
<img src="<%=Page.ResoveUrl("~/Images/footerLogo.png") %>" />
Modifying this to remove the <% %> (<img src="/Images/footerLogo.png" />) block fixed the error, but I don't have any such tags on the master page this time (or any page that links to the page in question). Here's my code:
Imports MySql.Data
Imports MySql.Data.MySqlClient
Partial Class maintreservation
Inherits System.Web.UI.Page
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
If Not IsPostBack Then
getClients()
getDrivers()
getVehicles()
pnlDriven.Visible = False
pnlSelfDriven.Visible = False
If Not String.IsNullOrEmpty(Session("resid")) AndAlso Session("resid") IsNot Nothing Then
getReservation()
End If
End If
End Sub
Protected Sub getDrivers()
ddlDriver.ClearSelection()
Dim db As New Database
Dim sql As String = "select driverid, drivername from drivers order by drivername"
Dim dr As MySqlDataReader = db.GetReader(sql)
If dr.Read Then
ddlDriver.DataSource = dr
ddlDriver.DataTextField = "drivername"
ddlDriver.DataValueField = "driverid"
ddlDriver.DataBind()
End If
dr.Close()
ddlDriver.Items.Insert(0, New ListItem("Select a Driver", 0))
End Sub
Protected Sub getVehicles()
ddlVehicle.ClearSelection()
Dim db As New Database
Dim sql As String = "select veh.vehicleid, veh.licence_plate, veh.model, vm.make from vehicles veh " & _
"inner join vehicle_manufacturers vm on veh.make = vm.makeid order by veh.make"
Dim dr As MySqlDataReader = db.GetReader(sql)
While dr.Read
ddlVehicle.Items.Add(New ListItem(dr("make") & " " & dr("model") & " " & " (" & dr("licence_plate") & ")", dr("vehicleid")))
End While
dr.Close()
ddlVehicle.Items.Insert(0, New ListItem("Select a Vehicle", 0))
End Sub
Protected Sub getClients()
ddlClient.ClearSelection()
Dim db As New Database
Dim sql As String = "select clientid, clientname, contact from clients order by clientname"
Dim dr As MySqlDataReader = db.GetReader(sql)
If dr.Read Then
ddlClient.DataSource = dr
ddlClient.DataTextField = "clientname"
ddlClient.DataValueField = "clientid"
ddlClient.DataBind()
End If
dr.Close()
ddlClient.Items.Insert(0, New ListItem("Select an Agent", 0))
getClientContact()
End Sub
Protected Sub getClientContact()
Dim db As New Database
Dim sql As String = "select contact, vat_no from clients where clientid = " & ddlClient.SelectedItem.Value
Dim dr As MySqlDataReader = db.GetReader(sql)
If dr.Read Then
If Not IsDBNull(dr("contact")) Then
lblClientContact.Text = dr("contact")
Else
lblClientContact.Text = ""
End If
If Not IsDBNull(dr("vat_no")) Then
txtVatNo.Text = dr("vat_no")
Else
txtVatNo.Text = ""
End If
End If
dr.Close()
End Sub
Protected Sub ddlClient_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ddlClient.SelectedIndexChanged
getClientContact()
End Sub
Protected Sub getReservation()
Dim db As New Database
Dim sql As String = _
"select * from reservations res " & _
"inner join reservationbody trip on res.reservationid = trip.reservationid " & _
"inner join vehicles vehicle on trip.vehicleid = vehicle.vehicleid " & _
"left outer join drivers driver on trip.driverid = driver.driverid " & _
"where res.reservationid = " & Session("resid")
Dim dr As MySqlDataReader = db.GetReader(sql)
If dr.Read Then
' GET CLIENT
' -------------------------------------------------------------
ddlClient.ClearSelection()
ddlClient.Items.FindByValue(dr("clientid")).Selected = True
getClientContact()
' GET VOUCHER
' -------------------------------------------------------------
If IsDBNull("vouchernumber") Then
txtVoucher.Text = ""
Else
txtVoucher.Text = dr("vouchernumber")
End If
' GET DRIVER
' -------------------------------------------------------------
If dr("driverid") = "0" Then
' Self Drive
rblTrips.Items(1).Selected = True
pnlDriven.Visible = False
pnlSelfDriven.Visible = True
Else
' Driven
rblTrips.Items(0).Selected = True
pnlSelfDriven.Visible = False
pnlDriven.Visible = True
ddlDriver.ClearSelection()
ddlDriver.Items.FindByValue(dr("driverid")).Selected = True
End If
' GET PASSENGER/S
' -------------------------------------------------------------
If IsDBNull(dr("passengers")) Then
txtPassengers.Text = ""
Else
txtPassengers.Text = dr("passengers")
End If
If IsDBNull(dr("passengercontact")) Then
txtPassengerContact.Text = ""
Else
txtPassengerContact.Text = dr("passengercontact")
End If
' GET COMMENTS
' -------------------------------------------------------------
If IsDBNull(dr("comments")) Then
txtComments.Text = ""
Else
txtComments.Text = dr("comments")
End If
' GET VEHICLES
' -------------------------------------------------------------
ddlVehicle.ClearSelection()
ddlDriver.Items.FindByValue(dr("vehicleid")).Selected = True
' GET DATES AND TIMES
' -------------------------------------------------------------
txtPickupDate.Text = Left(dr("res_date"), 10) ' USE DATE(trip.res_date) as res_date in the sql statement
ucTimeIn.Time = dr("time_in")
ucTimeOut.Time = dr("time_out")
End If
dr.Close()
End Sub
Protected Sub rblTrips_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles rblTrips.SelectedIndexChanged
If rblTrips.SelectedItem.Value = "driven" Then
pnlDriven.Visible = True
pnlSelfDriven.Visible = False
Else
pnlSelfDriven.Visible = True
pnlDriven.Visible = False
End If
End Sub
End Class
As stated, this code executes perfectly, so I'm really at a loss as to what the problem is here.
I've tried Cleaning and Rebuilding the Solution, but it still hasn't fixed anything, so any insights are welcome!
Ortund3 Answers
Input from Cory made me decide to go back and check that every DropDownList had only 1 selection specified and that's when I found the problem.
In getReservation() above:
' GET DRIVER
' -------------------------------------------------------------
If dr("driverid") = "0" Then
' Self Drive
rblTrips.Items(1).Selected = True
pnlDriven.Visible = False
pnlSelfDriven.Visible = True
Else
' Driven
rblTrips.Items(0).Selected = True
pnlSelfDriven.Visible = False
pnlDriven.Visible = True
ddlDriver.ClearSelection()
ddlDriver.Items.FindByValue(dr("driverid")).Selected = True
End If
And then later:
' GET VEHICLES
' -------------------------------------------------------------
ddlVehicle.ClearSelection()
ddlDriver.Items.FindByValue(dr("vehicleid")).Selected = True
This was just bad copy/paste, so for people viewing this answer, make 100% sure that you're only selecting ONCE
As a side note, I'm told that the following is better practice:
' Do this:
ddlVehicles.SelectedValue = dr("vehicleid")
' Instead of this:
ddlVehicles.Items.FindByValue(dr("vehicleid").Selected = True
While any ListControl is being rendered, a flag is set if it encounters more than one selected item. If the flag is true, the abstract method VerifyMultiSelect is called. DropDownList's implementation of VerifyMultiSelect throws an exception if it encounters multiple selected items, so the only possible reason you're seeing this exception is because you have multiple ListItems with Selected set to true within one of your DropDownLists.
I would carefully examine the results of your SQL to determine if there's a case where more than one item in the same DropDownList is having its Selected property set to true. There are three lines of code in the getReservation() function in your sample above that alter this property.
Perhaps it's the way you handle IsPostBack. There's a previously selected item stored in ViewState for that control, and you're trying to select another value along with it after post-back.
EDIT: OP found a solution.
Cᴏʀʏ
CommunityI had a similar issue when reworking someone elses old code. For me it was a view state issue that was addressed simply by calling
myDropDown.ClearSelection();
They were pulling the datasource for the dropdown from an enum without a key and thus using FindText to make a selection. If the dropdown selected item was changed however they re-ran the statement on PostBack with the FindText without first calling
myDropDown.ClearSelection();
which as per Corys reply meant two items - the one just selected plus the one already selected in viewstate - were now selected and an exception was therefore thrown.
Not sure how it ever worked but it wasn't exposed until some minor change was made to code. So if anyone is struggling to find duplicate lines of code as per OPs answer, then you might also want to consider view state mechanics on post back.
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