How to SELECT a dropdown list item by value programmatically

If you know that the dropdownlist contains the value you're looking to select, use:

ddl.SelectedValue = "2";

If you're not sure if the value exists, use (or you'll get a null reference exception):

ListItem selectedListItem = ddl.Items.FindByValue("2");

if (selectedListItem != null)
{
    selectedListItem.Selected = true;
}

Please try below:

myDropDown.SelectedIndex = 
myDropDown.Items.IndexOf(myDropDown.Items.FindByValue("myValue"))

combobox1.SelectedValue = x;

I suspect you may want yo hear something else, but this is what you asked for.

ddlPageSize.Items.FindByValue("25").Selected = true;

If anyone else is trying this and facing problem then let me point one possible problem: If you are using Web Application then inside Page_Load if you are loading drop-down from DB and at the sametime you want to load data, then first load your drop-down lists and then load your data with selected drop-down conditions.

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        LoadDropdown(); //drop-downs generated first
        LoadData(); // other data loading and drop-down value selection logic here
    }
}

And for successfully selecting drop-down from code follow the approved answer above which is

ddl.SelectedValue = "2";.

Hope it solves the problem