How: Get value of dropdownlist in a loop?

**santanamariscal** · 06-17-2004, 07:23 PM

Ok,
I can get the value of a dropdownlist buy doing this: dropdownlist1.selecteditem.value, i have left the default id for all the dropdownlists i have on the page. What I am trying to do is get the value in a loop. here is a simple example of what i am trying to do and what.

dim temp as string
for i=1 to 10
temp = dropdownlist(i).selecteditem.value
next

Obviously that didn't work so i tryed

temp = dropdownlist"+cstr(i)+".selecteditem.value

that also is not working, can anyone help.

Thank you,

Santana

**geirdude** · 06-21-2004, 09:49 AM

I have enclosed a commonly used utility class ControlInfo that is very useful..

Use this as follows.

ASPX CODE

Code:

INSERT ASPX PAGE DIRECTIVE HERE!!!!

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
  <HEAD>
    <title>WebForm1</title>
<meta content="Microsoft Visual Studio .NET 7.1" name=GENERATOR>
<meta content="Visual Basic .NET 7.1" name=CODE_LANGUAGE>
<meta content=JavaScript name=vs_defaultClientScript>
<meta content=http://schemas.microsoft.com/intellisense/ie5 name=vs_targetSchema>
  </HEAD>
<body MS_POSITIONING="GridLayout">
<form id=Form1 method=post runat="server"><asp:dropdownlist id=DropDownList1 style="Z-INDEX: 101; LEFT: 32px; POSITION: absolute; TOP: 120px" runat="server" AutoPostBack="True">
<asp:ListItem Value="e">e</asp:ListItem>
<asp:ListItem Value="f">f</asp:ListItem>
</asp:dropdownlist><asp:dropdownlist id=DropDownList2 style="Z-INDEX: 102; LEFT: 32px; POSITION: absolute; TOP: 160px" runat="server" AutoPostBack="True">
<asp:ListItem Value="c">c</asp:ListItem>
<asp:ListItem Value="d">d</asp:ListItem>
</asp:dropdownlist><asp:dropdownlist id=DropDownList3 style="Z-INDEX: 103; LEFT: 32px; POSITION: absolute; TOP: 200px" runat="server" AutoPostBack="True">
<asp:ListItem Value="a">a</asp:ListItem>
<asp:ListItem Value="b">b</asp:ListItem>
</asp:dropdownlist><asp:Button id="Button1" style="Z-INDEX: 104; LEFT: 24px; POSITION: absolute; TOP: 24px" runat="server" Text="Button"></asp:Button><asp:Button id="Button2" style="Z-INDEX: 105; LEFT: 24px; POSITION: absolute; TOP: 56px" runat="server" Text="Button"></asp:Button><asp:Label id="Label1" style="Z-INDEX: 106; LEFT: 112px; POSITION: absolute; TOP: 32px" runat="server">Label</asp:Label></FORM>

  </body>
</HTML>

VB.NET code behind

Code:

Public Class WebForm1
    Inherits System.Web.UI.Page

#Region " Web Form Designer Generated Code "

    'This call is required by the Web Form Designer.
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()

	End Sub
	Protected WithEvents DropDownList1 As System.Web.UI.WebControls.DropDownList
	Protected WithEvents DropDownList2 As System.Web.UI.WebControls.DropDownList
	Protected WithEvents DropDownList3 As System.Web.UI.WebControls.DropDownList
	Protected WithEvents Button1 As System.Web.UI.WebControls.Button
	Protected WithEvents Button2 As System.Web.UI.WebControls.Button
	Protected WithEvents Label1 As System.Web.UI.WebControls.Label

    'NOTE: The following placeholder declaration is required by the Web Form Designer.
    'Do not delete or move it.
    Private designerPlaceholderDeclaration As System.Object

    Private Sub Page_Init(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Init
        'CODEGEN: This method call is required by the Web Form Designer
        'Do not modify it using the code editor.
        InitializeComponent()
    End Sub

#End Region

	Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
		Dim ctrlInfo As ControlInfo() = ControlUtil.TraverseControls(Me.Page, "System.Web.UI.WebControls.DropDownList")
		Dim temp As String
		For i As Integer = 1 To 3
			For Each ctrl As ControlInfo In ctrlInfo
				Dim ddl As DropDownList = CType(ctrl.Control, System.Web.UI.WebControls.DropDownList)
				Dim sid As String = ddl.ID
				Dim n As Integer = CInt(Mid(sid, Len("DropDownList") + 1, Len(sid) - Len("DropDownList")))
				If n = i Then
					temp = temp & "Drop down " & i & " has value=" & ddl.SelectedValue & "<br>"
				End If
			Next
		Next
		Label1.Text = temp
	End Sub

End Class



Public Class ControlInfo
	Private _ID As String
	Private _type As Type
	Private _control As System.Web.UI.Control

	Public Sub New(ByVal id As String, ByVal type As Type, ByVal Control As Object)
		_ID = id
		_type = type
		_control = Control
	End Sub

	Public Property ID() As String
		Get
			Return _ID
		End Get
		Set(ByVal Value As String)
			_ID = Value
		End Set
	End Property

	Public Property TheType() As Type
		Get
			Return _type
		End Get
		Set(ByVal Value As Type)
			_type = Value
		End Set
	End Property

	Public Property Control() As Object
		Get
			Return _control
		End Get
		Set(ByVal Value As Object)
			_control = Value
		End Set
	End Property

	Public ReadOnly Property TypeName() As String
		Get
			Return _type.ToString()
		End Get
	End Property

End Class


Public Class ControlUtil

	Public Shared Function TraverseControls(ByVal root As System.Web.UI.Control, ByVal filter As Type) As ControlInfo()
		If root.Controls.Count > 0 Then

			Dim al As ArrayList = New ArrayList
			Dim s As String = root.GetType().ToString
			If Type.Equals(root.GetType(), filter) Then
				al.Add(New ControlInfo(root.ID, root.GetType(), root))
			End If
			For Each myCtrl As System.Web.UI.Control In root.Controls
				Dim tmpCtrlInfo As ControlInfo() = TraverseControls(myCtrl, filter)
				If Not tmpCtrlInfo Is Nothing Then
					al.AddRange(tmpCtrlInfo)
				End If
			Next
			Return CType(al.ToArray(GetType(ControlInfo)), ControlInfo())
		Else
			If Type.Equals(root.GetType(), filter) Then
				Return New ControlInfo() {New ControlInfo(root.ID, root.GetType(), root)}
			Else
				Return Nothing
			End If
		End If
	End Function

	Private Shared Function InFilter(ByVal ArrFilter() As String, ByVal Value As String) As Boolean
		For i As Integer = 0 To ArrFilter.Length - 1
			If Trim(LCase(ArrFilter(i))) = Trim(LCase(Value)) Then
				Return True
			End If
		Next
		Return False
	End Function

	Public Shared Function TraverseControls(ByVal root As System.Web.UI.Control, ByVal filterList As String) As ControlInfo()
		Dim filter() As String
		filter = Split(filterList, ",")
		If root.Controls.Count > 0 Then
			Dim al As ArrayList = New ArrayList
			Dim s As String = root.GetType().ToString
			If InFilter(filter, s) Then
				al.Add(New ControlInfo(root.ID, root.GetType(), root))
			End If
			For Each myCtrl As System.Web.UI.Control In root.Controls
				Dim tmpCtrlInfo As ControlInfo() = TraverseControls(myCtrl, filterList)
				If Not tmpCtrlInfo Is Nothing Then
					al.AddRange(tmpCtrlInfo)
				End If
			Next
			Return CType(al.ToArray(GetType(ControlInfo)), ControlInfo())
		Else
			Dim s As String = root.GetType().ToString
			If InFilter(filter, s) Then
				Return New ControlInfo() {New ControlInfo(root.ID, root.GetType(), root)}
			Else
				Return Nothing
			End If
		End If
	End Function

	Public Shared Function TraverseControls(ByVal root As System.Web.UI.Control) As ControlInfo()
		If root.Controls.Count > 0 Then
			Dim al As ArrayList = New ArrayList
			al.Add(New ControlInfo(root.ID, root.GetType(), root))
			For Each myCtrl As System.Web.UI.Control In root.Controls
				al.AddRange(TraverseControls(myCtrl))
			Next
			Return CType(al.ToArray(GetType(ControlInfo)), ControlInfo())
		Else
			Return New ControlInfo() {New ControlInfo(root.ID, root.GetType(), root)}
		End If
	End Function

End Class

**geirdude** · 06-21-2004, 10:00 AM

Just a small note on this code

This seems a lot of code for such a small task - however, the general idea of iterating through the page controls recursively is a common method. The outer loop in the Page Load event is really not needed, and not too efficient, but it does what it says

**makaveiljojo** · 05-22-2014, 10:35 PM

What an interesting topic to me, I never considered such a thing before. I think I obtained a lot of knowledge from this thread towards the C# DropDown List control.

**mariajohn** · 05-03-2018, 05:31 AM

Great topic! I never know about drop-down list in a loop thank for tell now I should also apply this one

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