Working with DropDownList and ListBox Controls in ASP.NET

C#DataSet Web Controls System.ComponentModel System.ReflectionListBox ControlsConvertToStringDropDownList ControlsFieldinfoGetConverterGetStandardValuesTypeDescripter ClassWeb Controls to Display DataWorking with DropDownList Control in ASP.NETWorking with ListBox Control in ASP.NET

13 Comments

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Erik N Minnie Llanos5y ago
I am building a currency converter and I want to add a way to prevent selecting the same currency in the drop down lists.
Ramesh Palaniappan10y ago
Nice
kalu singh rao10y ago
Nice...
Thiruppathi R10y ago
Nice..
anil babu14y ago
I have one requirement Drop down list to choose types: NFC/RFID reader when user choose reader show description in Label Description for RFID Reader : Reading range 6-12 Meteres. Description for NFC Reader : Reading Range 3-5 mm.
Durga15y ago
Hi, I am using a dropdown where I bind the items from the database.I have two items from the db for eg: Say I have "One" and "Two" as items in the dropdown, now I want to add an item dynamically from my C# program say "-select One-" and this item should be the default item in the dropdown on every page load. Please help me for the same.
vidya m p16y ago
i have 2 radio button if i select one corresponding field with drop down list have to get enabled and wen i select the other....the other option have to get enabled... example... complaint urgency (two radio button) complaint class ( dropdownlist of classes) urgency (drop down list of urgency) when i select the radio button complaint the complaint class have to get enabled and when i select urgency the corresponding field have to get enabled vidya
Anjaneya Prasad16y ago
i need to display all the details in textboxes like ename,sal,job,location etc by selecting eno using dropdownlist... plsss help me
bhayyasaheb kamble17y ago
i want code of drop down list .. for ex. if select state than city list will be enabled ...
Jeff Wollschlager17y ago
I have a dropdown list that displays a a returned items from a dataset. How might I make that a unique list of values if the dataset returns a duplicates?
- Gary Irons17y ago
  One way to accomplish this is to filter the data coming from the database by including the Distinct clause in your SQL statement. So the command might look like this Select Distinct ProductID from Products This would show only one occurence of a given ProductID even though there may be several.
shashi sahay18y ago
I am using dropdownlist in my ecommerce sit.I want when i click on dropdown only information for click item will display either in text box or in grid
sravanthi reddy19y ago
i have two drop down in one have category and other subcategory. now i if i select category automatically the subcategory should display in dropdown 2.evrything should come from database only.plz help me out.. script i am using is c#.net.if i click on submit button the detials should display in grid view using backend.

Introduction

This article is based on queries in the newsgroup:

Query 1 :"In my application i am using dropdownlist to display all categories from a table. When the user clicks this control I display all records in that category. Category table also contains column called color.

I wanted display some categories in dropdown list different color and others in different color using ASP.NET."-Anonymous

So data in the database along with the desired output is as given below

Note: The dropDownList has a bug which prevent us from assigning the style property to each item in the DropDownList.

So as stated by the MS Article the alternative method to achieve this is by using the tag given below:

<SELECT id="DropDownList1" name="DropDownList1" runat="server"></SELECT>

Now our code. As far as coding the steps we would follow are as below:

Fill the DataSet
Populate the DropDownList with the DataSet
Navigate through the DropDownList to give appropriate color to each item in the dropdown.

SqlConnection mycn;
SqlDataAdapter myda;
DataSet ds;
String strConn;
private void Page_Load(object sender, System.EventArgs e)
{
if (!IsPostBack)
{
strConn = "Data Source=localhost;uid=sa;pwd=;Initial Catalog=northwind";
mycn = new SqlConnection(strConn);
myda = new SqlDataAdapter("Select * FROM CategoryTable ", mycn);
ds = new DataSet();
myda.Fill(ds, "Table");
DropDownList1.DataSource = ds.Tables[0];
DropDownList1.DataTextField = ds.Tables[0].Columns["CategoryName"].ColumnName.ToString();
DropDownList1.DataValueField = ds.Tables[0].Columns["CategoryId"].ColumnName.ToString();
DropDownList1.DataBind();
for (int i = 0; i < DropDownList1.Items.Count; i++)
{
DropDownList1.Items[i].Attributes.Add("style", "color:" + ds.Tables[0].Rows[i]"CategoryColor"].ToString() );
}
}

VB.NET

Dim myconnection As SqlConnection
Dim myda As SqlDataAdapter
Dim ds As DataSet
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
myconnection =New SqlConnection("Server=localhost;uid=sa;password=;database=northwind;")
myda =New SqlDataAdapter("Select * from CategoryTable ", myconnection)
ds =New DataSet
myda.Fill(ds, "AllTables")
DropDownList1.DataSource = ds
DropDownList1.DataSource = ds.Tables(0)
DropDownList1.DataTextField = ds.Tables(0).Columns("CategoryName").ColumnName.ToString()
DropDownList1.DataValueField = ds.Tables(0).Columns("CategoryId").ColumnName.ToString()
DropDownList1.DataBind()
Dim i As Integer
For i = 0 To DropDownList1.Items.Count - 1
DropDownList1.Items(i).Attributes.Add("style", "color:" + ds.Tables(0).Rows(i)"CategoryColor").ToString())
Next
End Sub

Query 2 :"Is it possible for a listbox to show Products having Price above a specific value in one color and the ones below that value in different color"-Anonymous

To solve this the concept remains same only thing we need to do is use the ListBox and navigate through each and every record in dataset to have item with appropriate color. So lets consider the Products Table in Northwind Database and expect the output as below:

Tag that we use:

<SELECT id="listBox1" size="10" runat="server" NAME="listBox1"></SELECT>

Coding Step:

Populate the dataset
Navigate through the Rows checking for the value in the DataBase and the specific value (in our case its set to 25)
Depending on the value assign the style property for each item in the ListBox

Code given below:

C#

SqlConnection mycn;
SqlDataAdapter myda;
DataSet ds;
String strConn;
private void Page_Load(object sender, System.EventArgs e)
{
if (!IsPostBack)
{
strConn = "Data Source=localhost;uid=sa;pwd=;Initial Catalog=northwind";
mycn = new SqlConnection(strConn);
myda = new SqlDataAdapter("Select * FROM Products ", mycn);
ds = new DataSet();
myda.Fill(ds, "Table");
for (int i = 0; i < ds.Tables[0].Rows.Count - 1; i++)
{
listBox1.Items.Add(new ListItem(ds.Tables[0].Rows[i]["UnitPrice"].ToString(), ds.Tables[0].Rows[i]["ProductID"].ToString()));
if (Convert.ToDouble(ds.Tables[0].Rows[i]["UnitPrice"].ToString()) <= 25)
{
listBox1.Items[i].Attributes.Add("style", "color:red");
}
else
{
listBox1.Items[i].Attributes.Add("style", "color:green");
}
}
}
}

VB.NET

Dim myconnection As SqlConnection
Dim myda As SqlDataAdapter
Dim ds As DataSet
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
myconnection =New SqlConnection("Server=localhost;uid=sa;password=;database=northwind;")
myda =New SqlDataAdapter("Select * from Products ", myconnection)
ds =New DataSet
myda.Fill(ds, "AllTables")
Dim i As Integer
For i = 0 To ds.Tables(0).Rows.Count - 1
listBox1.Items.Add(New ListItem(ds.Tables(0).Rows(i)("UnitPrice"), ds.Tables(0).Rows(i)("ProductID")))
If ds.Tables(0).Rows(i)("UnitPrice") <= 25 Then
listBox1.Items(i).Attributes.Add("style", "color:red")
Else
listBox1.Items(i).Attributes.Add("style", "color:green")
End If
Next
End Sub

Sample Code

As we have done the coding for assigning style property to each item we might as well complete the code to develop a Color Picker in ASP.NET as below:

So the control we use is

<SELECT id="DropDownList1" name="DropDownList1" runat="server"></SELECT>

And code for this is as below:

Method 1

We'll use the namespace System.Reflection to get the FieldInfo (i.e. Colors)

using System.Reflection;

VB.NET

Imports System.Reflection

private void Page_Load(object sender, System.EventArgs e)
{
if (!IsPostBack)
{
foreach (FieldInfo col in typeof(KnownColor).GetFields())
{
if (col.FieldType == typeof(KnownColor))
{
DropDownList1.Items.Add(new ListItem(col.Name, col.Name));
}
}
}
for (int i = 0; i < DropDownList1.Items.Count; i++)
{
DropDownList1.Items[i].Attributes.Add("style", "background-color:" + DropDownList1.Items[i].Text);
}
}

VB.NET

Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
If Not Page.IsPostBack Then
Dim col As FieldInfo
For Each col In GetType(KnownColor).GetFields
If col.FieldType Is GetType(Drawing.KnownColor) Then
DropDownList1.Items.Add(New ListItem(col.Name, col.Name))
End If
Next
End If
Dim i As Integer
For i = 0 To DropDownList1.Items.Count - 1
DropDownList1.Items(i).Attributes.Add("style", "background-color:" + DropDownList1.Items(i).Text)
Next
End Sub

Method 2

The other way this can be done is by using Namespace System.ComponentModel and TypeDescripter Class.

using System.ComponentModel;

VB.NET

Imports System.ComponentModel

private void Page_Load(object sender, System.EventArgs e)
{
if (!IsPostBack)
{
foreach (Color c in TypeDescriptor.GetConverter(typeof(Color)).GetStandardValues())
{
ListItem li = new ListItem();
li.Text = TypeDescriptor.GetConverter(c).ConvertToString(c);
this.DropDownList1.Items.Add(li);
}
}
for (int i = 0; i < DropDownList1.Items.Count; i++)
{
DropDownList1.Items[i].Attributes.Add("style", "background-color:" + DropDownList1.Items[i].Text);
}
}

VB.NET

Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
If Not Page.IsPostBack Then
Dim c As Color
For Each c In TypeDescriptor.GetConverter(GetType(Color)).GetStandardValues()
Dim li As New ListItem
li.Text = TypeDescriptor.GetConverter(c).ConvertToString(c)
Me.DropDownList1.Items.Add(li)
Next c
End If
Dim i As Integer
For i = 0 To DropDownList1.Items.Count - 1
DropDownList1.Items(i).Attributes.Add("style", "background-color:" + DropDownList1.Items(i).Text)
Next
End Sub