MVVM Datagrid Binding SelectedItem not updating - wpf

Question

I'm new to WPF and MVVM and i've an applicaton that uses Entity Framework to connect to database and a datagrid to show the users of the application.
The users CRUD operations are made in a separate window and not in the datagrid.
My problems are related with the update of datagrid.
The insert operation is ok but the update is not.
View 1 (Users List):
<DataGrid Grid.Row="1"
ItemsSource="{Binding Users, Mode=TwoWay}"
SelectedItem="{Binding SelectedUser, Mode=TwoWay}"
AutoGenerateColumns="False"
CanUserAddRows="False">
</DataGrid>
ViewModel :
class UserListViewModel: NotificationClass
{
UserDBContext _db = null;
public UserListViewModel()
{
_db = new UserDBContext();
Users = new ObservableCollection<User>(_db.User.ToList());
SelectedUser = Users.FirstOrDefault();
}
private ObservableCollection<User> _users;
public ObservableCollection<User> Users
{
get { return _users; }
set
{
_users = value;
OnProprtyChanged();
}
}
private User _selectedUser;
public User SelectedUser
{
get
{
return _selectedUser;
}
set
{
_selectedUser = value;
OnProprtyChanged();
}
}
public RelayCommand Edit
{
get
{
return new RelayCommand(EditUser, true);
}
}
private void EditUser()
{
try
{
UserView view = new UserView();
view.DataContext = SelectedUser;
view.ShowDialog();
if (view.DialogResult.HasValue && view.DialogResult.Value)
{
if (SelectedUser.Id > 0){
User updatedUser = _db.User.First(p => p.Id == SelectedUser.Id);
updatedUser.Username = SelectedUser.Username; //this doesn't do nothing, object is already with the new username ?!
}
_db.SaveChanges();
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
}
}
after _db.SaveChanges(), datagrid should not be updated ?
Model:
class UserDBContext: DbContext
{
public UserDBContext() : base("name=DefaultConnection")
{
}
public DbSet<User> User { get; set; }
}
View 2 (User detail)
public partial class UserView : Window
{
public UserView()
{
InitializeComponent();
}
private void SaveButton_Click(object sender, RoutedEventArgs e)
{
DialogResult = true;
}
}
User object
class User: NotificationClass
{
public int Id { get; set; }
public string Username { get; set; }
public string CreatedBy { get; set; }
public DateTime? CreatedOn { get; set; }
}
NotificationClass
public class NotificationClass : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged = delegate { };
public void OnProprtyChanged([CallerMemberName]string propertyName = null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
if i close and open view 1, the new username is updated..
could someone help ? thanks

Answer 1

Just implementing INotifyPropertyChanged isn't enough, you have to explicitly invoke PropertyChanged (or in your case OnPropertyChanged) when a property changed.
See also https://learn.microsoft.com/en-us/dotnet/framework/wpf/data/how-to-implement-property-change-notification
You can do it like so
class User : NotificationClass
{
private int _id;
private string _username;
private string _createdBy;
private DateTime? _createdOn;
public int Id
{
get => _id;
set
{
if (value == _id) return;
_id = value;
OnPropertyChanged();
}
}
public string Username
{
get => _username;
set
{
if (value == _username) return;
_username = value;
OnPropertyChanged();
}
}
public string CreatedBy
{
get => _createdBy;
set
{
if (value == _createdBy) return;
_createdBy = value;
OnPropertyChanged();
}
}
public DateTime? CreatedOn
{
get => _createdOn;
set
{
if (value.Equals(_createdOn)) return;
_createdOn = value;
OnPropertyChanged();
}
}
}

Answer 2

it worked ! many thanks #nosale !
what about the change made to SelectedUser being reflected in my context ?
if i do this :
SelectedUser.Username = "test";
User updatedUser = _db.User.First(p => p.Id == SelectedUser.Id);
i was thinking that SelectedUser object has the "test" username and updatedUser has the old username, but not .. updatedUser already have "test"