How to implement Search in DropDownList in ASP.Net

Refer

Filter and Search ASP.Net DropDownList items using JavaScript

MyDropDown.SelectedIndex = MyDropDown.Items.IndexOf(MyDropDown.Items.FindByValue(whatEverYouWannaSearch));

e.g 

string a = "Mango"
MyDropDown.SelectedIndex = MyDropDown.Items.IndexOf(MyDropDown.Items.FindByValue(a));