Programmatically adding dropdownlist's. However, I want to know how to check which one I selected to add functionality to

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I am programmatically adding comboboxes per each column count from a gridview. the gridview gets its column counts from an excel sheet being uploaded from another page. HOwever, i want to know lets say there are 20 columns in the gridview and i have 20 drop down list items added to the page. how can i tell which drop down list item was selected. each drop down is correlated to a row. so if there are 20 rows there are 20 drop down list items. Please help. Thanks.

DONT DOWN VOTE please help me understand my mistake in asking the question. THANKS

VB

trLists.Cells.Clear()
            For i As Integer = 0 To GridView1.Rows(0).Cells.Count - 1
                Dim dd1 As New DropDownList()
                dd1.ID = "dd1" + i.ToString()
                dd1.Width = Unit.Pixel(150)
                If GlobalVariable.Flag = "1B" Then
                    dd1.Items.Insert(0, New ListItem(String.Empty, String.Empty))
                    dd1.Items.Add("Borough/Zip Code")
                    dd1.Items.Add("Address No.")
                    dd1.Items.Add("Street Name")
                    dd1.Items.Add("Freeform")
                ElseIf GlobalVariable.Flag = "2" Then
                    dd1.Items.Insert(0, New ListItem(String.Empty, String.Empty))
                    dd1.Items.Add("Borough/Zip Code")
                    dd1.Items.Add("Street 1")
                    dd1.Items.Add("Street 2")
                ElseIf GlobalVariable.Flag = "3" Then
                    dd1.Items.Insert(0, New ListItem(String.Empty, String.Empty))
                    dd1.Items.Add("Borough/Zip Code")
                    dd1.Items.Add("On Street")
                    dd1.Items.Add("First Cross Street")
                    dd1.Items.Add("Second Cross Street")
                    dd1.Items.Add("Side Of The Street")
                ElseIf GlobalVariable.Flag = "3S" Then
                    dd1.Items.Insert(0, New ListItem(String.Empty, String.Empty))
                    dd1.Items.Add("Borough/Zip Code")
                    dd1.Items.Add("On Street")
                    dd1.Items.Add("First Cross Street")
                    dd1.Items.Add("Second Cross Street")
                ElseIf GlobalVariable.Flag = "BL" Then
                    dd1.Items.Insert(0, New ListItem(String.Empty, String.Empty))
                    dd1.Items.Add("Borough/Zip Code")
                    dd1.Items.Add("Block")
                    dd1.Items.Add("Lot")
                ElseIf GlobalVariable.Flag = "BN" Then
                    dd1.Items.Insert(0, New ListItem(String.Empty, String.Empty))
                    dd1.Items.Add("BIN Number")
                Else
                    dd1.Items.Insert(0, New ListItem(String.Empty, String.Empty))
                    dd1.Items.Add("Borough")
                    dd1.Items.Add("Street Name")
                End If
                Dim cell As New TableCell()
                cell.Controls.Add(dd1)
                trLists.Cells.Add(cell)
                GlobalVariable.dd1 = dd1
            Next

What I have tried:

i tried to post the same question on stack overflow but no one got it i think. this is why i chose code project.

Posted 21-Jun-16 5:40am

JT1992

Updated 7-Jul-16 6:01am

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Vincent Maverick Durano · Accepted Answer · 2016-06-23T05:57:00

To make it more clear to your side, I made another demo. We will add a Table, HiddenField, GridView and a Button control in the markup.

ASPX:

ASP.NET

<asp:table id="tbl1" runat="server" />
<asp:hiddenfield id="HiddenField1" runat="server" />
<asp:gridview id="GridView1" runat="server">
</asp:gridview>
<asp:button id="Button1" runat="server" onclick="Button1_Click" text="Button"/>

The table is where we generate the DropDownList based
The HiddenField is where we store the selected DropDown ID at SelectedIndexChanged event of DropDown
The GridView contains your data
The Button is where we get the value from HiddenField and display in a Message Box (alert)

Now here's the code block:

VB.NET

VB

Protected Sub Page_Load(sender As Object, e As EventArgs)
	If Not IsPostBack Then
			'bind  your grid here
		BindGridView()
	End If

	GenerateDropDowns(GridView1.Columns.Count)
End Sub

Private Sub GenerateDropDowns(colCount As Integer)

	Dim row As New TableRow()
	For i As Integer = 0 To colCount - 1
		Dim cell As New TableCell()
		Dim ddl As New DropDownList()
		ddl.ID = "ddl" + i.ToString()
		ddl.Items.Add(New ListItem("PASS", "P"))
		ddl.Items.Add(New ListItem("FAIL", "F"))
		ddl.AutoPostBack = True
		'wire up the event
		AddHandler ddl.SelectedIndexChanged, AddressOf OnSelectedIndexChanged

		cell.Controls.Add(ddl)

		row.Cells.Add(cell)
	Next
	tbl1.Rows.Add(row)
End Sub

Protected Sub OnSelectedIndexChanged(sender As Object, e As EventArgs)
	Dim ddl1 As DropDownList = DirectCast(sender, DropDownList)
	HiddenField1.Value = ddl1.ID
End Sub

Protected Sub Button1_Click(sender As Object, e As EventArgs)
	Dim theDropDown As String = HiddenField1.Value
	If theDropDown <> String.Empty Then
		Dim msgScript As String = String.Format("alert('You have selected: {0}');", theDropDown)
		Page.ClientScript.RegisterClientScriptBlock(Me.[GetType](), "Alert", msgScript, True)

			'reset
		HiddenField1.Value = String.Empty
	End If
End Sub

C# Equivalent:

C#

protected void Page_Load(object sender, EventArgs e) {
    if (!IsPostBack) {
        BindGridView();//bind  your grid here
    }

    GenerateDropDowns(GridView1.Columns.Count);
}

private void GenerateDropDowns(int colCount) {

    TableRow row = new TableRow();
    for (int i = 0; i < colCount; i++) {
        TableCell cell = new TableCell();
        DropDownList ddl = new DropDownList();
        ddl.ID = "ddl" + i.ToString();
        ddl.Items.Add(new ListItem("PASS", "P"));
        ddl.Items.Add(new ListItem("FAIL", "F"));
        ddl.AutoPostBack = true;
       //wire up the event
        ddl.SelectedIndexChanged += OnSelectedIndexChanged;

        cell.Controls.Add(ddl);
        row.Cells.Add(cell);

    }
    tbl1.Rows.Add(row);
}

protected void OnSelectedIndexChanged(object sender, EventArgs e) {
    DropDownList ddl1 = (DropDownList)sender;
    HiddenField1.Value = ddl1.ID;
}

protected void Button1_Click(object sender, EventArgs e) {
    string theDropDown = HiddenField1.Value;
    if (theDropDown != string.Empty) {
        string msgScript = string.Format("alert('You have selected: {0}');", theDropDown);
        Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "Alert", msgScript, true);

        HiddenField1.Value = string.Empty;//reset
    }
}

Hope that helps and clears your confusion.

Vincent Maverick Durano · Accepted Answer · 2016-06-21T05:58:00

Solution 1

You could wire-up the SelectedIndexChanged event of your DropDown. At SelectedIndexChanged event handler, you could cast the sender of the control to determine which row your triggered the DropDown event. For example:

Wireup the event:

C#

dd1.SelectedIndexChanged += OnSelectedIndexChanged;

VB.NET

VB

AddHandler dd1.SelectedIndexChanged, AddressOf OnSelectedIndexChanged

Then you can write the code to access the selected item like:

C#

C#

protected void OnSelectedIndexChanged(object sender, EventArgs e){
        DropDownList ddl1 = (DropDownList)sender;
        GridViewRow row = (GridViewRow)ddl1.NamingContainer;
        if (row != null)
        {
            string selectedItem = ddl1.SelectedItem.Text;
        }
}

VB.NET

VB

Protected Sub OnSelectedIndexChanged(sender As Object, e As EventArgs)
	Dim ddl1 As DropDownList = DirectCast(sender, DropDownList)
	Dim row As GridViewRow = DirectCast(ddl1.NamingContainer, GridViewRow)
	If row IsNot Nothing Then
		Dim selectedItem As String = ddl1.SelectedItem.Text
	End If
End Sub

Posted 21-Jun-16 5:58am

Vincent Maverick Durano

Updated 22-Jun-16 4:42am

v3

Comments

JT1992 21-Jun-16 11:59am

ahh let me try this and i will give you a quick reply. this seems to be what i was looking for.

Richard Deeming 21-Jun-16 12:05pm

VB doesn't use += to wire up event handlers - it uses AddHandler:
AddHandler dd1.SelectedIndexChanged, OnSelectedIndexChanged

And you haven't need the new EventHandler(...) decorator in VB or C# since .NET 1.0 - the compiler is smart enough to add that for you. :)
dd1.SelectedIndexChanged += OnSelectedIndexChanged;

Vincent Maverick Durano 21-Jun-16 12:18pm

I'm not a VB guy and I'm just using a converter tool to convert it to VB. So blame the tool ;) I updated my reply to add the correct syntax.

Thanks for the information. Much appreciated man! :)

JT1992 21-Jun-16 12:28pm

wait i am lost i dont get it so what should i use for code for the event handler?
the one listed above gives me to use a RaiseEvent Statement

Vincent Maverick Durano 21-Jun-16 12:31pm

Try this:

AddHandler dd1.SelectedIndexChanged, AddressOf OnSelectedIndexChanged

JT1992 21-Jun-16 14:39pm

thanks vincent. i am confused in where i would be able to add this handler.

Vincent Maverick Durano 21-Jun-16 14:42pm

place it before you add the control to the cells collection like:

AddHandler dd1.SelectedIndexChanged, AddressOf OnSelectedIndexChanged
cell.Controls.Add(dd1)

JT1992 21-Jun-16 14:44pm

but then how will i know which row the selected index was? like lets say if i select the 5th out of 20 drop down list item. how would i see the fifth one was selected?

Vincent Maverick Durano 21-Jun-16 14:48pm

I explained it in my first post. You can determine which dropdown triggers the event by casting the sender of the object.

Protected Sub OnSelectedIndexChanged(sender As Object, e As EventArgs)
Dim ddl1 As DropDownList = DirectCast(sender, DropDownList)
Dim row As GridViewRow = DirectCast(ddl1.NamingContainer, GridViewRow)
Dim rowIndex As Integer = row.RowIndex ' Get's the current row index of the grid
If row IsNot Nothing Then
Dim selectedItem As String = ddl1.SelectedItem.Text
End If
End Sub

JT1992 21-Jun-16 14:55pm

so is there a way to test this using a messagebox? just to get the value row index?

Vincent Maverick Durano 21-Jun-16 15:01pm

Just print it on the page using:

Response.Write(rowIndex)

Or better debug your code, set a break point at OnSelectedIndexChanged, and step into each line to see the actual values.

JT1992 21-Jun-16 15:59pm

what if i wanted this event to trigger on a click of a button? and then pop out a message box?

Vincent Maverick Durano 22-Jun-16 6:15am

If the button is inside your grid then you can follow the same code, but you would need to cast the sender to Button instead. If the button is outside then I'm afraid you can't.

JT1992 22-Jun-16 9:07am

thats the issue its outside. not sure how to test this code :/

Vincent Maverick Durano 22-Jun-16 9:10am

I'll try to create a sample demo if could hack it for you.

JT1992 22-Jun-16 10:18am

really appreciate the help once again.

Vincent Maverick Durano 22-Jun-16 10:45am

not a problem. just don't forget to close this thread so future readers can easily find the post that helps you. :) Thanks!

JT1992 22-Jun-16 9:12am

awesome thanks a lot.

Vincent Maverick Durano 22-Jun-16 10:41am

check Solution 2 for the solution. :)

Vincent Maverick Durano · Accepted Answer · 2016-06-22T04:40:00

Ok here's the other solution to your problem. The idea is use HiddenField control to store the selected rowIndex. Here's the demo code below:

ASPX:

ASP.NET

<asp:content id="Content2" contentplaceholderid="MainContent" runat="server" xmlns:asp="#unknown">
    <asp:gridview id="GridView1" runat="server" onrowcreated="GridView1_RowCreated">
        <columns>
                <asp:templatefield>
                    <itemtemplate>
                        <asp:hiddenfield id="HiddenField1" runat="server" value="0" />
                    </itemtemplate>
                </asp:templatefield>
         </columns>
    </asp:gridview>
    <asp:button id="Button1" runat="server" onclick="Button1_Click" text="Button" />
</asp:content>

CODE BEHIND:

C#

using System;
using System.Web.UI.WebControls;
using System.Data;
using System.Web.UI;

namespace WebFormDemo
{
    public partial class DynamicControlInGridView : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e) {
            if (!IsPostBack)
                BindGridView();
        }

        protected void GridView1_RowCreated(object sender, GridViewRowEventArgs e) {
            if (e.Row.RowType == DataControlRowType.DataRow) {
                DropDownList ddlResult = new DropDownList();
                ddlResult.ID = "ddlResult";
               
                ddlResult.Items.Add(new ListItem("PASS", "P"));
                ddlResult.Items.Add(new ListItem("FAIL", "F"));
                ddlResult.AutoPostBack = true;
                ddlResult.SelectedIndexChanged += OnSelectedIndexChanged;

                e.Row.Cells[0].Controls.Add(ddlResult);

            }
        }

        protected void OnSelectedIndexChanged(object sender, EventArgs e) {
            DropDownList ddl1 = (DropDownList)sender;
            GridViewRow row = (GridViewRow)ddl1.NamingContainer;
            if (row != null) {
                HiddenField hf = (HiddenField)row.FindControl("HiddenField1");
                hf.Value = row.RowIndex.ToString();
            }
        }

        private void BindGridView() {
            GridView1.DataSource = CreateDataSource();
            GridView1.DataBind();
        }

        public DataTable CreateDataSource() {
            DataTable dt = new DataTable();
            DataRow dr;

            dt.Columns.Add(new DataColumn("ID", typeof(string)));
            dt.Columns.Add(new DataColumn("Name", typeof(string)));
            dt.Columns.Add(new DataColumn("Lastname", typeof(string)));

            for (int i = 0; i < 20; i++) {
                dr = dt.NewRow();

                dr[0] = i;
                dr[1] = "Name" + i.ToString();
                dr[1] = "Last Name" + i.ToString();

                dt.Rows.Add(dr);
            }

            return dt;
        }

        protected void Button1_Click(object sender, EventArgs e) {

            foreach (GridViewRow row in GridView1.Rows) {
                HiddenField hf = (HiddenField)row.FindControl("HiddenField1");
                if (hf != null) {
                    int selectedRowIndex = Convert.ToInt32(hf.Value);
                    if (selectedRowIndex > 0) {
                        string msgScript = string.Format("alert('You have selected: {0}');", selectedRowIndex);
                        Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "Alert", msgScript, true);

                        hf.Value = "0";//reset
                        break;
                    }
                }              
            }
        }
       
    }
}

That should work. The code above is in C#. You may need to convert it VB before applying it. Hope that helps.