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Inconsistent behavior in GridViewDataColumn template binding

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Chris
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Chris asked on 17 May 2012, 02:47 PM
I have a column in my RadGridView that displays some text and then also contains a button that should only be visible to users with permission to change the data.  I'm using MVVM and the viewmodel exposes a boolean property named UserHasWriteAccess that indicates the user's permission level.  The column and its datatemplate are defined as follows.

<telerik:GridViewDataColumn Header="Reason Code">
    <telerik:GridViewDataColumn.CellTemplate>
        <DataTemplate>
            <Grid>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="*" />
                    <ColumnDefinition Width="Auto" />
                </Grid.ColumnDefinitions>
 
                <TextBlock Text="Lorem ipsum" />
                <Button Content="Edit"
                        Height="23"
                        HorizontalAlignment="Right"
                        Margin="4,0,0,0"
                        Visibility="{Binding DataContext.UserHasWriteAccess,
                                    Mode=OneTime,
                                    Converter={StaticResource BooleanToVisibilityConverter},
                                    RelativeSource={RelativeSource AncestorType=telerik:RadGridView}}">
            </Grid>
        </DataTemplate>
    </telerik:GridViewDataColumn.CellTemplate>
</telerik:GridViewDataColumn>

When UserHasWriteAccess is false, the button's visibility binding works fine most of the time (~99%) and the button does not show.  However, as the user scrolls up and down through the grid, eventually intermittent binding errors will suddenly appear for a row or two for which the binding worked previously.  Sometimes the user has to scroll up and down several times before it happens.  Other times it's immediate.  The errors say:

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='Telerik.Windows.Controls.RadGridView', AncestorLevel='1''. BindingExpression:Path=DataContext.UserHasWriteAccess; DataItem=null; target element is 'Button' (Name=''); target property is 'Visibility' (type 'Visibility')

Curiously, when I inspect an errored binding using Snoop, it suddenly works again.

Is there a known issue with ancestor binding in RadGridView?

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Pavel Pavlov
Telerik team
answered on 18 May 2012, 09:52 AM
Hi Chris,

For performance reasons RadGridView uses virtualization when scrolling . Cells and rows are being reused, recycled, added and removed to/from  the visual tree dynamically. This is why such bindings may occur unreliable. As a workaround I would recommend to expose the object with the relevant property as a static resource on the page. Then use binding to a static resource rather than binding to ancestor. This should do the trick. 

All the best,
Pavel Pavlov
the Telerik team

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Pavel Pavlov
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