Question

I have just started to create a user control realising that I want a lot more out of the DataGrid. Don’t worry about the details for now but I have created a DependencyProperty called TheColumns :

 public static readonly DependencyProperty TheColumnsProperty = DependencyProperty.Register("TheColumns", typeof(List<DataGridColumnItem>), typeof(ExtendedDataGrid), null);

DataGridColumnItem is just an independent class I created to hold column information etc.

I then declared a property to get and set the value :

 public List<DataGridColumnItem> TheColumns
 {
     get
     {
         return (List<DataGridColumnItem>)GetValue(TheColumnsProperty);
     } 
     set
     {
         SetValue(TheColumnsProperty, value);
         TheDataGrid.Columns.Clear();

         foreach (var col in TheColumns)
         {
             var newCol = new DataGridTextColumn();
             newCol.Header = col.Header;
             var columnBinding = new Binding(col.DataBindingMember);
             newCol.Binding = columnBinding;

             TheDataGrid.Columns.Add(newCol);
         }
    }
}

OK, this is all a simple test before I do it properly becase I wanted to set my columns from a view model, as there is no proper column binding in the dataGrid itself. Oh, I want to determin the colum order, visibility and what is actually going to be displayed at run time, not in xaml.

I have a property in my view model called GridColumns declared as :

public List<DataGridColumnItem> GridColumns ….

I have boud this property in xamle like :

TheColumns="{Binding Path=GridColumns}"

OK, now I created an instance of the view model and set it to the DataContext of the Window in which the user control is housed. When I run it, the property IS read from the view model but the setter on the dependency property does not fire. If I remode the xaml assignment the property on the view model does not fire. Therefore, the property is being read but not made use of.

Answer 1

You ran into this: Setters not run on Dependency Properties?
Essentially you need to hookup the PropertyChangedCallback and do your logic in there.