Caliburn Micro MVVM INotifyPropertyChange

Question

So I'm using Cliburn Micro and i have a Bindablecollection, lets call it users.

        public BindableCollection<UserModel> Users
    {
        get { return _users; }
        set
        {
            _users = value;
            NotifyOfPropertyChange(() => Users);

        }
    }

Now this is linked to a datagrid with two columns FirstName and LastName In another panel the selected item of the datagrid gets set

                <DataGrid x:Name="AllUsers" SelectionMode="Single" Margin="5"
                  SelectionUnit="FullRow" AutoGenerateColumns="False" 
                  CanUserAddRows="False" CanUserDeleteRows="False" 
                  CanUserReorderColumns="False" 
                  IsReadOnly="True" Style="{DynamicResource DataGridUsers}"
                  SelectedItem="{Binding Path=SelectedUser, Mode=TwoWay}"
                  cal:Message.Attach="[Event MouseDoubleClick] = [Action DoubleClickUser()]">
                <DataGrid.Columns>
                    <DataGridTextColumn Header="First Name" Binding="{Binding Path=FirstName}" Width="*"/>
                    <DataGridTextColumn Header="Last Name" Binding="{Binding Path=LastName}" Width="*"/>
                </DataGrid.Columns>
            </DataGrid>

Then i've created a TextBoxFirstName and i only set the value if its not null

                            <DockPanel>
                            <Label x:Name="LabelFirstName" Width="80" HorizontalContentAlignment="Left" VerticalAlignment="Center" Foreground="#FFAD231F" FontFamily="Lucida Sans Unicode" FontSize="12" >First Name</Label>
                            <TextBox x:Name="TextBoxFirstName" Margin="0,0,5,0" Text="{Binding 
                    UpdateSourceTrigger=PropertyChanged, Path=TextBoxFirstName,
                    ValidatesOnDataErrors=true, NotifyOnValidationError=true}" 
                    HorizontalAlignment="Stretch" Height="23" TextAlignment="Center" TextWrapping="NoWrap" VerticalAlignment="Top" Style="{StaticResource RoundedTextBox}" FontFamily="Lucida Sans Unicode"/>
                        </DockPanel>

My Error Validation over the textbox is,

        public string this[string columnName]
    {
        get
        {
            string result = null;
            if (columnName == "TextBoxFirstName")
            {
                if (string.IsNullOrEmpty(TextBoxFirstName))
                {
                    result = "Please enter a First Name";
                }
                else
                {
                    SelectedUser.FirstName = TextBoxFirstName;
                    NotifyOfPropertyChange(() => SelectedUser);
                }

            }
            return result;
        }
    }

Now I know SelectedUser.FirstName is updated as if i set another textbox databinding to SelectedUser.FirstName it updates as expected, but its not updating the Datagrid when i change it? but if i update the value in the secondtextbox (the one with the binding SelectedUser.FirstName) it does update the datagrid,

AnyIdeas?? Basically i only want to update the datagrid if the value in the textbox passes the validation. Assume i don't want to edit the values in the datagrid itself.

Driving me mad I know it must be with the way it notifies but i can't get it to work and im fairly new to c# and MVVM and WPF any help would be much appreciated. thanks

Answer 1

You need to NotifyOfPropertyChange on FirstName instead of SelectedUser. Preferably you should do this in the FirstName setter.

Answer 2

So, The way I was implementing the IDataError was wrong, you don't need to set the the value in an else statement. The way i should have implemented it.

Should have used it in my model not in the viewmodel.

Also My Model looks like this,

namespace App.Models
{
public class ConfigModel : INotifyPropertyChanged
{

    private bool _showConfig;

    public event PropertyChangedEventHandler PropertyChanged;

    public bool ShowConfig
    {

        get { return this._showConfig; }
        set
        {
            this._showConfig = value;
            this.OnPropertyChanged("ShowConfig");
        }
    }

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

Thanks for the help from Wes and Mark for pointing me in the right direction.