Update all parents when shared nested object gets updated - wpf

Question

I have below class hierarchy.
public class RowViewModel : BaseViewModel
{
private CellViewModel cell;
public CellViewModel Cell
{
get { return cell; }
set
{
cell = value;
OnPropertyChanged("Cell");
}
}
}
public class CellViewModel : BaseViewModel
{
public string Text { get { return string.Join("\n", CellLinks.Select(c => c.Text)); } }
private ObservableCollection<CellLinkViewModel> cellLinks;
public ObservableCollection<CellLinkViewModel> CellLinks
{
get
{ return cellLinks; }
set
{
cellLinks = value;
OnPropertyChanged("CellLinks");
}
}
}
public class CellLinkViewModel : BaseViewModel
{
public string Text
{
get { return CellValue.Text; }
set
{
CellValue.Text = value;
OnPropertyChanged("Text");
}
}
public CellValueViewModel CellValue { get; set; }
}
public class CellValueViewModel : BaseViewModel
{
public string Text { get; set; }
}
public class BaseViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChangedEventArgs e = new PropertyChangedEventArgs(propertyName);
PropertyChanged(this, e);
}
}
}
XAML code looks like,
<DataGrid ItemsSource="{Binding Rows}" AutoGenerateColumns="False">
<DataGrid.Columns>
<DataGridTemplateColumn Header="#" Width="200">
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<TextBlock Text="{Binding Cell.Text}"/>
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
<DataGridTemplateColumn.CellEditingTemplate>
<DataTemplate>
<ListBox ItemsSource="{Binding Cell.CellLinks}">
<ListBox.ItemTemplate>
<DataTemplate>
<TextBox Text="{Binding Text, Mode=TwoWay}"/>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
</DataTemplate>
</DataGridTemplateColumn.CellEditingTemplate>
</DataGridTemplateColumn>
</DataGrid.Columns>
</DataGrid>
CellValueViewModel is shared across multiple CellLinkViewModel. When I change CellValueViewModel it should have propagated changes to all dependent parents and DataGrid should show all latest values.
This is result
But I think its not happening automatically, am I missing something here? How to notify all datagrid cells to update automatically when the nested objects gets updated.

Answer 1

You need to hook up event handlers to the PropertyChanged event for all CellLinkViewModel objects and raise the PropertyChanged event for the Text property of the CellViewModel whenever a link is modified, e.g.:
public class CellViewModel : BaseViewModel
{
public string Text { get { return string.Join("\n", CellLinks.Select(c => c.Text)); } }
private ObservableCollection<CellLinkViewModel> cellLinks;
public ObservableCollection<CellLinkViewModel> CellLinks
{
get
{
return cellLinks;
}
set
{
cellLinks = value;
if(cellLinks != null)
{
foreach(var link in cellLinks)
{
link.PropertyChanged += Link_PropertyChanged;
}
}
OnPropertyChanged("CellLinks");
}
}
private void Link_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
OnPropertyChanged("Text");
}
}
You probably also want to handle the CollectionChanged event for the ObservableCollection<CellLinkViewModel> and hook up event handlers to dynamically added CellLinkViewModel objects as well.