Develop Reference

How to select an Item from asp:Dropdownlist on Page load from Code Behind C#?

I tried so many articles around, like below to get my task done, but didn't work as I always ends up with an NullReferenceException, I have bound a database table column to the Dropdown list, on page load i want to select an item based on the value from database which is one of those listed items. Please help me.
txt_examtype.DataSource = dt;//txt_examtype is the dropdownlist
txt_examtype.DataTextField = "ExamTypeName";
txt_examtype.DataValueField = "ExamTypeName";
txt_examtype.DataBind();
String examtype = dt.Rows[0]["ExamType"].ToString().Trim();
ListItem myitem = txt_examtype.Items.FindByValue(examtype);
txt_examtype.SelectedValue = myitem.Value;

try this code
txt_examtype.SelectedValue = dt.Rows[0]["ExamType"].ToString()

You should set SelectedIndex instead of SelectedValue. This is safe to use:
txt_examtype.SelectedIndex = txt_examtype.Items.IndexOf(txt_examtype.Items.FindByValue(examtype));

Set SelectedValue in DataGridViewComboBoxColumn or DataGridViewComboBoxCell

I would like to set a value to the ComboBox in the DataGridView. I already have changed the comboBoxItems, I just want to select one of them. Thank you in advance!!!

I already solved my problem... I'm gonna post the way I did and hoppefully someone will find this answer too.
dgrDetalle.DataSource = dataTable("select * from yourTable");
DataTable dtCombo = dataTableCombo("select COL_ID DETOC_COL_FK,COL_DESCRIPCION from yourTable2");
string[] strColumns = new string[] { "COL_DESCRIPCION" };
MultiColumnDictionary map = new MultiColumnDictionary(dtCombo, "DETOC_COL_FK", strColumns, 0);
dgrDetalle.Cols["DETOC_COL_FK"].DataMap = map;
As you can see the class that save my life is MultiColumnDictionary.
Note: The combobox items must be loaded in a different DatatTable than the DataTable that is gonna load directly in the grid.

As far as I know, the Comboboxes only actually exist as controls when they are being edited, and therefore don't have a selected item property.
You can simply set the Value property of the cell to the item you want selected, or alternitively, you can set a default value by setting the property:
DataGridViewColumn.DefaultCellStyle.NullValue.

How to get value from combobox in c#?

I can't get value from ComboBox in WinForms using C#.
I have a ComboBox populated with a list of values and I have set ValueMember and DisplayMember.
Now, I have to find the value of the selected ComboBox item and select the matched item in UI.
Here is what I mean:-
I loaded the ComboBox like this :-
var list = (from l in db.Loc
orderby l.LName ascending
select l).ToList();
list.Insert(0, new Loc { ID = "-1", Name = "--Select--" });
cmb1.BindingContext = new BindingContext();
cmb1.DataSource = list;
cmb1.DisplayMember = "Name";
cmb1.ValueMember = "ID";
Now on an event, I am trying to match value (ID) and select the item. It's easy if I match Text property:
cmb1.Text = data.Name;
But How to match the value?
Something like this:-
cmb1.Value = data.ID;

If you only know the ID of the item you can also use:
cmb1.SelectedValue = data.ID;

This should work:
cmb1.SelectedValue = data.ID;

Why would you like to assign you "matched" value to the ComboBox Value property?
As soon as you have correctly set DisplayMember and ValueMember and you DataSource implements both as properties the values will be autoamatically "matched", e.g. you can read the Value property in you event handler to get this "matched" value.

data must be in the list binded to the combobox, then:
cmb1.SelectedItem = data
or, if it's not (you retrieved another instance from somewhere):
cmb1.SelectedValue = data.ID

First of all: cmb1.Text = text; changes the text of the ComboBox to the specified value. It doesn't select the item with the text that matchs the specified value.
Use cmb1.SelectedValue = value; to select the item with the speciefied value.

You can get the index using Combo1.SelectedIndex property. You can get the item using either Combo1.SelectedItem or Combo1.Items[Combo1.SelectedIndex]

problem with drop down list

I have a drop down list control populated with items and some code to take the currently selected item value. The problem is I only get the value of the first item in the list regardless of what item is actually selected.
Here is my code to populate the drop down:
protected void displayCreateCategories()
{
StoreDataContext db = new StoreDataContext();
var a = from c in db.Categories
orderby c.Name
select new{catName= c.Name,
catId=c.CategoryID};
ddlCategory.DataSource = a;
ddlCategory.DataTextField = "catName";
ddlCategory.DataValueField = "catId";
ddlCategory.DataBind();
}
To get the value of the currently selected item which in my case is always of type integer I do label1.text=Convert.toInt32(ddlCategory.SelectedValue);
I get the selected value, but it is always for the 1st item in the list. I'm pulling my hair out over this. :(

I suspect you're running the list loading code every time the page loads, which is destroying the list, repopulating the list, and auto-selecting the first item before your selection retrieval code gets run.
Use this construction in Page_Load:
if (!IsPostBack)
{
// Initial control population goes here
}

Data binding will reset the control's selected value so make sure you retrieve the selected value before data binding on postback.

Setting dropdownlist selecteditem programmatically

I want to set the selecteditem attribute for an ASP.Net dropdownlist control programmatically.
So I want to pass a value to the dropdownlist control to set the selected item where the item is equal to the passed value.

Assuming the list is already data bound you can simply set the SelectedValue property on your dropdown list.
list.DataSource = GetListItems(); // <-- Get your data from somewhere.
list.DataValueField = "ValueProperty";
list.DataTextField = "TextProperty";
list.DataBind();
list.SelectedValue = myValue.ToString();
The value of the myValue variable would need to exist in the property specified within the DataValueField in your controls databinding.
UPDATE:
If the value of myValue doesn't exist as a value with the dropdown list options it will default to select the first option in the dropdown list.

ddlData.SelectedIndex will contain the int value To select the specific value into DropDown :
ddlData.SelectedIndex=ddlData.Items.IndexOf(ddlData.Items.FindByText("value"));
return type of ddlData.Items.IndexOf(ddlData.Items.FindByText("value")); is int.

Here is the code I was looking for :
DDL.SelectedIndex = DDL.Items.IndexOf(DDL.Items.FindByText("PassedValue"));
Or
DDL.SelectedIndex = DDL.Items.IndexOf(DDL.Items.FindByValue("PassedValue"));

Well if I understood correctly your question. The Solution for setting the value for a given dropdownlist will be:
dropdownlist1.Text="Your Value";
This will work only if the value is existing in the data-source of the dropdownlist.

If you need to select your list item based on an expression:
foreach (ListItem listItem in list.Items)
{
listItem.Selected = listItem.Value.Contains("some value");
}

Just Use this oneliner:
divisions.Items.FindByText("Some Text").Selected = true;
divisions.Items.FindByValue("some value").Selected = true;
where divisions is a dropdownlist control.
Hope it helps someone.

var index = ctx.Items.FirstOrDefault(item => Equals(item.Value, Settings.Default.Format_Encoding));
ctx.SelectedIndex = ctx.Items.IndexOf(index);
OR
foreach (var listItem in ctx.Items)
listItem.Selected = Equals(listItem.Value as Encoding, Settings.Default.Format_Encoding);
Should work.. especially when using extended RAD controls in which FindByText/Value doesn't even exist!

ddList.Items.FindByText("oldValue").Selected = false;
ddList.Items.FindByText("newValue").Selected = true;

On load of My Windows Form the comboBox will display the ClassName column of my DataTable as it's the DisplayMember also has its ValueMember (not visible to user) with it.
private void Form1_Load(object sender, EventArgs e)
{
this.comboBoxSubjectCName.DataSource = this.Student.TableClass;
this.comboBoxSubjectCName.DisplayMember = TableColumn.ClassName;//Column name that will be the DisplayMember
this.comboBoxSubjectCName.ValueMember = TableColumn.ClassID;//Column name that will be the ValueMember
}

Safety check to only select if an item is matched.
//try to find item in list.
ListItem oItem = DDL.Items.FindByValue("PassedValue"));
//if exists, select it.
if (oItem != null) oItem.Selected = true;

ddlemployee.DataSource = ds.Tables[0];
ddlemployee.DataTextField = "Employee Name";
ddlemployee.DataValueField = "RecId";
ddlemployee.DataBind();
ddlemployee.Items.Insert(0, "All");