In my MVVM model I have named a UserControl like:
x:Name="root"
In my viewmodel have a bool called AllChecked and as the name indicates this should be bound to a checkbox in the xaml file indicating whether all rows in a datagrid should be checked or unchecked.
In my xaml file I have a datagrid like:
<DataGrid ItemsSource="{Binding SomeObservableCollection, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}">
<DataGrid.Columns>
<DataGridCheckBoxColumn Binding="{Binding IsSelected, UpdateSourceTrigger=PropertyChanged}"
<DataGridCheckBoxColumn.Header>
<CheckBox IsChecked="{Binding DataContext.AllChecked, ElementName=root, Mode=TwoWay}" HorizontalAlignment="Center"/>
</DataGridCheckBoxColumn.Header>
</DataGridCheckBoxColumn>
<DataGridTextColumn Header="Column A" Binding="{Binding Path=a}" Width="120" IsReadOnly="true"/>
<DataGridTextColumn Header="Column B" Binding="{Binding Path=b, StringFormat=dd-MM-yyyy}" Width="120" IsReadOnly="true"/>
<DataGridTextColumn Header="Column C" Binding="{Binding Path=c}" Width="90" IsReadOnly="true"/>
<DataGridTextColumn Header="Column D" Binding="{Binding Path=d}" IsReadOnly="true" Width="130" />
</DataGrid.Columns>
</DataGrid>
When I start the application the binding of AllChecked does not work, the error being that
"Cannot find source: ElementName = root"
If I delete root from ElementName and rewrite it again, it suddenly works. I have no idea what is going on, but it seems like some kind of timing issue where the binding is set before the x:Name of the UserControl is defined, maybe?
Anyone able to help here?
The column does not belong to the logical tree of the DataGrid. So WPF doesn't know where to get the DataContext. The typical solution to this problem is something called a BindingProxy. Read this:
https://thomaslevesque.com/2011/03/21/wpf-how-to-bind-to-data-when-the-datacontext-is-not-inherited/