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How to get asp.net dropdownlist to allow selections

I have a dropdownlist on a webform that I fill from a sql query, I then want to be able to select individual items in the dropdown and have corresponding fields from a datatable fill textboxes on the form
Problem is rowSel is returning 0 and the dropdown won't let me select any other item it always snaps back to the first itenm in the list.
Thought this might have something to do with autopostback being set to true, but if I set it to false that causes otheer problems, Not sure what else to try Im a winforms person and very new to asp.net
protected void ddClients_SelectedIndexChanged(object sender, EventArgs e)
{
int rowSel = ddClients.SelectedIndex;
txtClient.Text = dsShow.Rows[rowSel["ClientsTableFieldA"].ToString();
}
It should allow me to select a value from the drop down then populate some textboxes with fields from the datatable.

You could try:
protected void ddClients_SelectedIndexChanged(object sender, EventArgs e)
{
txtClient.Text = ddClients.SelectedItem.Value.ToString();
}

protected void ddClients_SelectedIndexChanged(object sender, EventArgs e)
{
txtClient.Text = ddClients.SelectedItem.Text;
}
As suggested by B. Seberle
DDL items have fields value and text so it depends how you bound the ddl to SQL datasource.
place break point on txtClient.Text = ddClients.SelectedItem.Text see if item list is empty.
it should not be necessary but you can force a ddClient.databind() in page_load if(!Page.IsPostback).
however ddClients_SelectedIndexChanged will only trigger on postback.

asp.net dropdownlist does not remember choice

I'm currently running into a head-scratching bug in my ASP.NET Windows Form App. I have two DropDownList, implemented them in the same way, yet they behave differently.
The problem:
When selecting an item in the DropDownList "GroepSelect", the page refreshes (as intended), but resets it's SelectedIndex to the first item.
When selecting an item in the DropDownList "VakSelect", the page refreshes, but also remembers it's SelectedIndex value.
It's doing this behavior consistently, yet I am unable to discover what I do wrong.
My Code:
In my HTML code, I have two DropDownList Controls.
<div>
<asp:DropDownList runat="server" ID="GroepSelect" AutoPostBack="true" AppendDataBoundItems="true" />
<asp:DropDownList runat="server" ID="VakSelect" AutoPostBack="true" AppendDataBoundItems="true" />
</div>
I'm populating the controls in my C# code:
protected void Page_Load(object sender, EventArgs e) {
Database db = new Database();
if (!IsPostBack) {
GroepSelect.DataSource = GenereerDummyGroepen(); // returns a List<ListItem>
GroepSelect.DataTextField = "Text";
GroepSelect.DataValueField = "Value";
GroepSelect.DataBind();
GroepSelect.SelectedValue = "1";
VakSelect.DataSource = db.GetVakken(); // returns a List<Vak>
VakSelect.DataTextField = "Omschrijving";
VakSelect.DataValueField = "Id";
VakSelect.DataBind();
VakSelect.SelectedValue = "1";
}
// Use the SelectedValue to determine which data to get out of the database
Medewerkers = db.GetMedewerkers(int.Parse(GroepSelect.SelectedValue));
Opdracht = db.GetOpdrachten(int.Parse(VakSelect.SelectedValue)).First();
Resultaten = db.GetResultaten(Opdracht.Id, int.Parse(GroepSelect.SelectedValue));
GenereerTabel();
}
As requested, my code for GenereerDummyGroepen() is the following:
private List<ListItem> GenereerDummyGroepen() {
return new List<ListItem>()
{
new ListItem("Groep 1", "1"),
new ListItem("Groep 2", "1")
};
}
Why I implemented it this way?
I try to populate a custom-made pivot table based on the content of Medewerkers, Opdracht and Resultaten. The content of those lists, depends on the selected item in the DropDownList control. The expected behavior of those controls is, that on the moment those are changed, the table should re-populate. The strategy I follow here, is that a page-postback is being processed, and using the AppendDataBoundItems=true remembers the DropDownList contents so that on the newly refreshed page I can generate the table.
My Question
I'm looking for the answer for: why is there a consistent different behavior? Is it the fact that the ListItem class differs in behavior from my custom class Vak?

Here I guess issue is with you function
GenereerDummyGroepen();
Please put your code here. In your code there is value field might have same data for all listItem. Because of that it is changing default to firstIndex as all values are same.

Asp.net Dropdownlist : Want to hide the initial value when page loaded for second time

I created a dropdown list and then added items to it with an initial value of -1 with text "select country"
My question is: when I select something from the list and later on change my mind to one item to another item. Now I wanted to hide the initial value "select country" from the list on postback

Check inside postback that if dropdownlist value has been selected than disable the "Select Country" option
if(IsPostBack)
{
if(ddlCountry.SelectedIndex>0)
ddlCountry.Items.FindByValue("-1").Enabled = false;
}

You can write like this in page load
protected void Page_Load(object sender, EventArgs e)
{
if(IsPostBack)
{
if(DropDownList1.SelectedIndex>0)
DropDownList1.Items.FindByValue("-1").Enabled = false;
}
}

Dropdown List not returning the correct value

i am trying to retrieve the value on a previously databinded DropDownList like this:
<asp:DropDownList ID="DropDownListReception" runat="server" CssClass="span3 drop-down-reception"
OnPreRender="DropDownListReception_PreRender" OnSelectedIndexChanged="DropDownListReception_SelectedIndexChanged" AutoPostBack="true"></asp:DropDownList>
protected void Page_Load(object sender, EventArgs e)
{
var receptions = BLLFactory.ReceptionBLL.GetListAll();
DropDownListReception.DataSource = receptions;
DropDownListReception.DataBind();
}
On the DropDown PreRender i am personalizing this DropDown like this:
protected void DropDownListReception_PreRender(object sender, EventArgs e)
{
if (DropDownListReception.DataSource != null)
{
DropDownListReception.Items.Clear();
DropDownListReception.Items.Add(new ListItem("-- Select --", "NA"));
foreach (Reception item in (DropDownListReception.DataSource as IEnumerable))
{
DropDownListReception.Items.Add(new ListItem(item.Name + " " + item.Number, item.Id.ToString()));
}
}
}
this is working perfectly, my DropDown loads as it should, my problem is when i try to retrieve the SelectedValue in the SelectedIndexChanged event, it wont return the value as a string but as a type, what i am doing is:
protected void DropDownListReception_SelectedIndexChanged(object sender, EventArgs e)
{
//CurrentReception is a string i want to save in ViewState
//I also tried (sender as DropDownList).SelectedValue
//Tried DropDownListReception.SelectedValue
CurrentReception = DropDownListReception.SelectedItem.Value;
}
but this "DropDownListReception.SelectedItem.Value" will always return "Reception" which is the type of the item, not the id i assigned as the item value in the PreRender event. This also happens if i do this: "DropDownListReception.SelectedItem.Text", this also return "Reception". How can i return the string Value i assigned to the DropDown item?

var CurrentReception = DropDownListReception.SelectedItem as Reception;
string val = CurrentReception.PropertyYouNeed;

DropDownListReception.SelectedItem.Text and DropDownListReception.SelectedItem.Value will return the value of the selection, which is the second term in the ListItem used when you add it to the list. In other words, the problem is with item.Id.ToString(). It returns the type of the object instead of the ID. I'm not sure what your item object actually consists of so I'm not sure what you actually need, but are you sure it's not just item.Id? ToString() is generally the string representation of the object, if item.Id is an int, then ToString should give you the string equivalent of that int... but the fact that it doesn't work suggests item.Id is not actually an int.

I think you need to cast the list item to the type that you stored in it (Reception), then access the property from the Reception object that you want (from your description it sounds like you want the id). Like this:
protected void DropDownListReception_SelectedIndexChanged(object sender, EventArgs e)
{
//CurrentReception is a string i want to save in ViewState
CurentReception = ((Reception)DropDownListReception.SelectedItem).Id.ToString();
}

I figured it out, i was DataBinding the DropDownList on the PageLoad, which fires before the SelectedIndexChanged event. Since the DropDown does a PostBack when its value changes, the PageLoad was "Recreating" the DropDown and i was losing the changes before getting to the SelectedIndexChanged code.
Thank you all for your answers.:)

Dropdownlist first value display "choose"

I want that my dropdownlist display first value: "-choose car-"
I succeed at this way:
protected void ddl1_DataBound(object sender, EventArgs e)
{
Convert.ToInt32(ddl1.SelectedValue);
ddl1.Items.Insert(0, new ListItem("-Choose car-", "-Choose car-" ));
}
and that's ok,the "-choose-" is in the first place but the problem now is that if I have values,for example,the dropdownlist show like that:
-Choose car-
Subaro
Fiat
Honda
The first value that display when I'm enter to the site is the Subaro,and to see the -choose car- the user need to open the dropdownlist and then he will see the -choose car- at the first place.How can I do that from the start,from the page load - the -choose car- will display at the ddl from the page load.Where I wrong at the code ?
I tried the itemlist with AppendDataBoundItems = "true" but I got an error, and when I succeed,the problem is the same like I said before.

You were on the right track with using the AppendDataBoundItems property, it should be set to true if you're databinding the list.
Your markup should look like this
<asp:DropDownList runat="server" ID="ddl1" AppendDataBoundItems="true">
<asp:ListItem Text="-Choose car-" />
</asp:DropDownList>
and your code behind probably already looks something like this
ddl1.DataSource = [your datasource goes here];
ddl1.DataBind();
This will place the Choose car text as the first option in the drop-down list and append the rest of the options below it.
Now for the more interesting part of why you were seeing the behavior you were seeing (first item not being selected). If you look at the implementation of SelectedIndex using a tool like JustDecompile (not affiliated with Telerik, just happen to use their tool) you'll see code that looks like this:
public int SelectedIndex
{
get
{
int num = 0;
num++;
while (num < this.Items.Count)
{
if (this.Items[num].Selected)
{
return num;
}
}
return -1;
}
set
{
// stuff you don't care about
this.ClearSelection();
if (value >= 0)
{
this.Items[value].Selected = true;
}
// more stuff you don't care about
}
}
As you can see, the index isn't stored anywhere, it's computed every time based on which item has the Selected property set to true. When you set the SelectedIndex to 0 in the markup and databind your datasource, it will select the 0th item in that list, in your case Subaro. When you insert a new item at the beginning of the list, Subaro is still marked as the selected item, which is why when the page loads, you see that selected and not Choose car. If you want to mark Choose car as the selected item using code, you will have to do it after you data databind your dropdown. Please note, this is just an implementation detail of how DropdownList works. It could change in future version of ASP.NET so do not write code that relies on it working this way.

Make sure that you bind the data source and insert you "-choose care-" item first before selected he first item
make sure when you insert your 1st item "-Choose car-" you make it once not on each PostBack. Check if not IsPostBack to add the 1st item.
EDIT:
Example:
protected void Page_Load(object sender, EventArgs e)
{
if(!IsPostBack)
{
ddl1.Items.Insert(0, new ListItem("-Choose car-", "-Choose car-" ));
}
ddl1.SelectedIndex = 0;
}

You should do ddl1.Items.Insert(0, new ListItem("-Choose car-", "-Choose car-")); first, and than ddl1.SelectedIndex = 0

private void FillCar()
{
DataTable dt = GetCar();
ddl1.Items.Clear();
ddl1.DataSource = dt;
ddl1.DataTextField = "carName"; // field name in the database
ddl1.DataValueField = "CarNum"; // field name in the database
ddl1.DataBind();
ListItem li = new ListItem();
li.Text = "--Choose car--";
li.Value = "-1";
ddl1.Items.Insert(0, li);
ddl1.SelectedIndex = 0;
}
I use method like this and call it in the page load in if (!IsPostBack){}.