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In my SilverLight application, I have a property in my ViewModel called 'vmProperty' and a list called 'dgSource'.

I bind my dgSource to the datagrid as ItemsSource at which point each datagrid row's datacontext changes to each item in dgSource. One of the columns, say a checkbox column, needs to bind to vmProperty. But since the ViewModel is no longer the row's datacontext, I cannot get access to this property.

How do I get around this problem? If the question is not clear, please let me know and I will post a sample. Thanks in advance.

etrast81
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  • Do really intend for each checkbox instance for each row to bind back to the same property on the parent object, doesn't seem to make a lot of sense to me? – AnthonyWJones Dec 01 '09 at 12:11

2 Answers2

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Try to set checked property of your chechbox column to that:

{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type YourViewClassName}}, Path=DataContext.vmProperty}

That's mean that parent element which type is your view type will be found and than vmProperty of it's DataContext will be retrieved as value.

UPDATE:

It was solution for WPF.

For silverlight I think you can try to use construction like this:

{Binding Path=DataContext.vmProperty, ElementName=YourElement}

Where DataContext of YourElement is instance of your view model. I think it can be a grid for example.

<Grid x:Name="YourElement" DataContext={Binding}>
<!-- DataGrid here -->
</Grid>
bniwredyc
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Assuming your ViewModel is assigned as the LayoutRoot's DataContext this should work:- 

IsChecked="{Binding DataContext.vmProperty, ElementName=LayoutRoot}"

Of course this doesn't work, ultimately a template is replicated and therefore "LayoutRoot" does not exist in the namescope where the binding is actually used.

The simplest solution since this is a ViewModel is to change the model. Expose the required value on the objects available in the dgSource or expose a Parent property that navigates back to the ViewModel.

AnthonyWJones
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  • Thanks for your responses. I used the ElementName method you have mentioned. But I run into the same issue as in 'http://stackoverflow.com/questions/1089650/silverlight-datagrid-celltemplate-binding-to-viewmodel'. I put this outside the datagrid and this piece code works great. But within the datagrid it doesnt. Anyways, I used the link provided in that thread 'http://blogs.msdn.com/jaimer/archive/2008/11/22/forwarding-the-datagrid-s-datacontext-to-its-columns.aspx', but that seems to be relevant only for WPF. I am unable to access AddOwner or OverrideMetadata. Thoughts? – etrast81 Dec 01 '09 at 18:10
  • Thanks Anthony, Managed to expose it as part of dgSource. Not happy about it as it is replication. But it is working. So... :) – etrast81 Dec 02 '09 at 10:52
  • Thats the advantage of a __view__ model. It would be most unsatisfactory if it were simply the __model__ but the whole point of a view model is that its munged form of data that supports a specific view or task. – AnthonyWJones Dec 02 '09 at 11:00