Question

I am trying to bind a combo box to a list of objects, and it works great, besides the selected value, am I missing somethign?

<ComboBox ItemsSource="{Binding OrderInfoVm.AllCountries}"
          SelectedValuePath="country_code" DisplayMemberPath="country_name" 
          SelectedValue="{Binding OrderInfoVm.BillingCountry}" />

Basically I want to bind value to country codes and set the selected value to the country code bound to OrderInfoVm.BillingCountry (which implements INotifyPropertyChanged)

Initially when the control loads selected value is empty, but on click BillingCountry is populated. Selected value does not seem to change. How can I remedy that?

Answer 1

I do agree with Alex that using SelectedItem gives the desired behaviour. See the code below. It works and will hopefully help you further:

    <Window x:Class="SelectedValueSpike.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300">
    <StackPanel>
        <ComboBox ItemsSource="{Binding OrderInfoVm.AllCountries}" 
          SelectedValuePath="country_code" DisplayMemberPath="country_name"  
          SelectedItem="{Binding OrderInfoVm.BillingCountry}"
          IsSynchronizedWithCurrentItem="True"
          Name="AllCountriesBox"/>
        <TextBox Text="{Binding ElementName=AllCountriesBox, Path=SelectedValue}"/>
        <Button>
            Change the textbox to "Ca","NL",or "US" and click!
        </Button>
    </StackPanel>
</Window>

    using System.Collections.ObjectModel;
    using System.ComponentModel;
    using System.Windows;

    namespace SelectedValueSpike
    {
        public partial class Window1 : Window
        {
            public OrderInfoVm OrderInfoVm{ get; set;}
            public Window1()
            {
                InitializeComponent();
                OrderInfoVm=new OrderInfoVm();
                OrderInfoVm.AllCountries.Add(new Country("US","US of A"));
                OrderInfoVm.AllCountries.Add(new Country("NL","Netherlands"));
                OrderInfoVm.AllCountries.Add(new Country("Ca","Canada"));
                OrderInfoVm.BillingCountry = OrderInfoVm.AllCountries[1];
                DataContext = this;
            }
        }



public class OrderInfoVm:INotifyPropertyChanged
    {
        public OrderInfoVm()
        {
            AllCountries=new ObservableCollection<Country>();
        }

        public event PropertyChangedEventHandler PropertyChanged;

        private ObservableCollection<Country> _allCountries;
        public ObservableCollection<Country> AllCountries
        {
            get { return _allCountries; }
            set
            {
                _allCountries = value;
                OnPropertyChanged("AllCountries");
            }
        }

        private Country _billingCountry;
        public Country BillingCountry
        {
            get { return _billingCountry; }
            set
            {
                _billingCountry = value;
                OnPropertyChanged("BillingCountry");
            }
        }

        private void OnPropertyChanged(string property)
        {
            if(PropertyChanged!=null)
                PropertyChanged(this,new PropertyChangedEventArgs(property));
        }
    }

    public class Country
    {
        public string country_code { get; set; }
        public string country_name { get; set; }

        public Country(string code, string name)
        {
            country_code = code;
            country_name = name;
        }
    }
}