[Solved] GridViewComboBoxColumn - ItemsSourceBinding

[JS]

Hi

I am trying to bind a GridViewComboBoxColumn to a property in my ViewModel.

For example:
A view "HomeView" with DataContext "HomeViewModel"
"HomeViewModel" has an observable collection "Tasks". Each task has a property "TypeId".
"HomeViewModel" has an observable collection "Types".

The GridView has ItemsSource="{Binding Path=Tasks}"
The GridView has a GridViewComboBoxColumn that should list all "Types".

If I use ItemsSource="{Binding Path=Types}" for the column, the column will be blank until focused.
When I click on the column, the values appear. When the column looses focus, the entire column is blank.

If I use ItemsSourceBinding="{Binding Path=Types}" for the column, the binding will search for a property "Types" in the "Task"

I have tried binding to "ElementName", and "Path=DataContext.Types", where ElementName refers to the View, but this did not work.

I have found these solutions to be working, but both might be a problem if I am using d:DataContext for designtime support:
ItemsSourceBinding="{Binding Path=FindShared[HomeViewModel].Types, Source={StaticResource VMLocator}}"
(http://johnpapa.net/silverlight/simple-viewmodel-locator-for-mvvm-the-patients-have-left-the-asylum/)
Each call to "FindShared" will result in 6 bindings, and will be a performance problem.

This seems to be a better solution:
ItemsSourceBinding="{Binding Path=DataSource.Types, Source={StaticResource DataContextProxy}}"
http://weblogs.asp.net/dwahlin/archive/2009/08/20/creating-a-silverlight-datacontext-proxy-to-simplify-data-binding-in-nested-controls.aspx


Do you have other better solutions for binding a ViewModel property to the ItemsSource in the GridViewComboBoxColumn?

regards
JS

[Pavel Pavlov]

Hi JS,

The root of the problem is that ElementName binding is not currently supported inside cells( due to cell virtualization) . Additionally the cells have the business object stored in the ItemsSource collection  as DataContext rather than the whole view model.

So there are two possible workarounds :

1. Set the ItemsSource  for the ComboBox column form codebehind , rather than binding in XAML .
OR
2. Expose the ItemsSource as static resource in XAML and use the  {Binding ..., Source= {StaticResource ...}}  syntax.

Sincerely yours,
Pavel Pavlov
the Telerik team

[Peter]

Can you expand on #2 "Expose the ItemsSource as static resource in XAML and use the  {Binding ..., Source= {StaticResource ...}}  syntax."

Thanks,

Peter Pepperell

[Yavor Georgiev]

Hello Peter,

 What you need to do is to expose your ViewModel as a StaticResource like so:

<UserControl.Resources>
  <local:HomeViewModel x:Key="MyViewModel" />
</UserControl.Resources>

 And then:

<telerik:GridViewComboBoxColumn DataMemberBinding="{Binding TypeId}" ItemsSourceBinding={Binding Types, Source={StaticResource MyViewModel}}" />

 If exposing your ViewModel as a StaticResource is unfeasible, you should instead use a DataContextProxy, as you cannot bind to a property of another element's DataContext in Silverlight.

Kind regards,
Yavor Georgiev
the Telerik team