Workaround for binding expression list on binding group being empty

16
votes

In WPF 4 the binding expression list on the binding group, which is passed to the ValidationRule's Validate method, is empty.

It is the same whether AutoGenerateColumns is true or false, whether DataGridBoundColumns explicitly has been added to the datagrid.

In WPF 3.5 SP1 using the DataGrid from the Toolkit the binding expression list is filled with the excepted binding expressions (1 for each column in the data grid)

I consider this a bug and has posted it on the Microsoft Connect site: https://connect.microsoft.com/WPF/feedback/details/642815/bindingexpressions-on-bindinggroup-passed-to-validationrule-in-datagrid-rowvalidationrules-is-empty

But does anyone have a workaround so I can get the correct binding expression from within the ValidationRule?

1
wpfvalidationdata-binding

1 Answers

1
votes

In order to support "proposed values" that are not committed to the target of a two-way binding until validation succeeds, the WPF 4.0 DataGrid was redesigned to take advantage of the the new BindingGroup.SharesProposedValues feature of WPF 4.0. Because of this change, it is no longer necessary to use two-way bindings in binding group of display templates.

You can use BindingGroup.TryGetValue to retrieve the proposed values for other columns instead of using the old method that worked with the DataGrid from the WPF Toolkit.

In other words, the new DataGrid actually fixes an undesirable feature of the old DataGrid and as a result things work slightly differently (i.e. the missing bindings are by design) but you can still do what you need to do.

The explanation in Microsoft's own words is in this Microsoft Connect link:

And here is a blog that describes BindingGroup.SharesProposedValues in another way: