WPF C# datagrid combobox on new row won't update datasource (updated!)

Question

This is an example exhibiting the behaviour I'm having trouble with. I have a datagrid which is bound to an observable collection of records in a viewmodel. In the datagrid I have a DataGridTemplateColumn holding a combobox which is populated from a list in the viewmodel. The datagrid also contains text columns. There are some textboxes at the bottom of the window to show the record contents.

Initially there are no records so the datagrid is empty and shows just one line containing the combobox. If the user enters data into the text columns first then a record is added to the collection and the combobox value can be added to the record. However, if the user selects the combobox value first, then the value disappears when another column is selected. How do I get the combobox data added to the record if it is selected first?

Codebehind:

public partial class MainWindow : Window
{
    public GridModel gridModel { get; set; }

    public MainWindow()
    {
        InitializeComponent();
        gridModel = new GridModel();
        //dgCustomers.DataContext = gridModel;
        this.DataContext = gridModel;
    }

    private void cmbCountry_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        ComboBox c = sender as ComboBox;
        Debug.Print("ComboBox selection changed, index is " + c.SelectedIndex + ", selected item is " + c.SelectedItem);
    }
}

The Record class:

public class Record : ViewModelBase
{
    private string _name;
    public string name
    {
        get { return _name; }
        set
        {
            _name = value;
            OnPropertyChanged("name");
        }
    }

    private string _phone;
    public string phone
    {
        get { return _phone; }
        set
        {
            _phone = value;
            OnPropertyChanged("phone");
        }
    }

    private int _countryCode;
    public int countryCode
    {
        get { return _countryCode; }
        set
        {
            _countryCode = value;
            OnPropertyChanged("countryCode");
        }
    }
}

Country class:

public class Country : ViewModelBase
{
    private string _name;
    public string name
    {
        get { return _name; }
        set
        {
            _name = value;
            OnPropertyChanged("name");
        }
    }

    private int _id;
    public int id
    {
        get { return _id; }
        set
        {
            _id = value;
            OnPropertyChanged("id");
        }
    }

    private int _code;
    public int code
    {
        get { return _code; }
        set
        {
            _code = value;
            OnPropertyChanged("code");
        }
    }

    public override string ToString()
    {
        return _name;
    }
}

GridModel:

public class GridModel : ViewModelBase
{
    public ObservableCollection customers { get; set; }
    public List countries { get; set; }
    public GridModel()
    {
        customers = new ObservableCollection();
        countries = new List { new Country { id = 1, name = "England", code = 44 }, new Country { id = 2, name = "Germany", code = 49 },
        new Country { id = 3, name = "US", code = 1}, new Country { id = 4, name = "Canada", code = 11 }};
    }

    private Country _selectedCountry;
    public Country SelectedCountry
    {
        get
        {
            return _selectedCountry;
        }
        set
        {
            _selectedCountry = value;
            _selectedRow.countryCode = _selectedCountry.code;
            OnPropertyChanged("SelectedRow");
        }
    }

    private Record _selectedRow;
    public Record SelectedRow
    {
        get
        {
            return _selectedRow;
        }
        set
        {
            _selectedRow = value;
            Debug.Print("Datagrid selection changed"); 
            OnPropertyChanged("SelectedRow");
        }
    }
}

Converters:

class Converters
{
}

public class SelectedRowConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value is Record)
            return value;
        return new Customer.Record();
    }
}

ViewModelBase:

public class ViewModelBase : INotifyPropertyChanged
{
    public ViewModelBase()
    {

    }

    public event PropertyChangedEventHandler PropertyChanged;

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

Sandesh · Accepted Answer

The behaviour you are seeing is as expected. The reason behind it is that the ComboBox ItemsSource as well as SelectedItem both are bound to Properties of the Window's DataContext while the other columns are bound to your DataGrid's ItemsSource. Hence when you modify the columns other than the dropdown the data is added to the observable collection.

What you can do is after a value is selected from the drop down you need to add a record yourself (possibly by calling a function from your SelectedCountry property)

EDIT

Based on your code I made a working model making as little changes as possible to your existing code. I could not use the converter as I did not have the details of the class Customer

Xaml

Your GridModel class

public class GridModel : ViewModelBase
{
    public ObservableCollection customers { get; set; }
    public ObservableCollection countries
    {
        get;
        private set;
    }
    public GridModel()
    {
        customers = new ObservableCollection { };
        AddUserCommand = new RelayCommand(AddNewUser);
        countries = new ObservableCollection 
        { 
            new Country { id = 1, name = "England", code = 44 },
            new Country { id = 2, name = "Germany", code = 49 },
            new Country { id = 3, name = "US", code = 1},
            new Country { id = 4, name = "Canada", code = 11 }
        };
    }

    private void AddNewUser()
    {
        customers.Add(new Record());
    }

    public ICommand AddUserCommand { get; set; }

    private Record _selectedRow;
    public Record SelectedRow
    {
        get
        {
            return _selectedRow;
        }
        set
        {
            _selectedRow = value;
            Debug.Print("Datagrid selection changed");
            OnPropertyChanged("SelectedRow");
        }
    }
}

I have used MVVMLight toolkit which contains RelayCommand. You can also define your own ICommand implementation and use it instead of the toolkit

EDIT 2

Fixed the bug introduced by me which would prevent the combobox from displaying the Country if the data comes from the data base. The improved code does not require any converter either

WPF C# datagrid combobox on new row won't update datasource (updated!)

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