Question

Is there a build procedure in C# for making a combobox or list box that has names of all countries and when a country is selected another combobox is filled with the cities of that country?

Answer 1

Sure there is a procedure. You could start with a simple data structure:

public class Country {   public string Name { get; set; }   public IList<City> Cities { get; set; }    public Country()   {     Cities = new List<City>();   } }  public class City { public string Name { get; set; } } 

Then, instantiate this structure, e.g. into a property of your form…

Countries =   new List<Country>     {       new Country         {           Name = 'Germany',           Cities =             {               new City {Name = 'Berlin'},               new City {Name = 'Hamburg'}             }         },       new Country         {           Name = 'England',           Cities =             {               new City {Name = 'London'},               new City {Name = 'Birmingham'}             }         }     }; 

In your form, instantiate two Binding Sources (BS):

• The first BS binds to the Countries property.
• The second BS binds to the first (DataSource = firstBS) and its DataMember should be ‘Cities’.

Now you need two dropdowns:

• 1st: DataSource = first BS, DisplayMember = ‘Name’
• 2nd: DataSource = second BS, DisplayMember = ‘Name’

and you should be pretty much done.