I would like to bind third column to a CollectionBindingTwo
property that is within Window's DataContext and not inside DataContext of an Items from CollectionBindingOne
.
By defining the second collection inside <DataGrid>
WPF assumes local scope or something, and points to a property within Items of ItemsSource ( CollectionBindingOne
).
<DataGrid DockPanel.Dock="Top" ItemsSource="{Binding CollectionBindingOne}" AutoGenerateColumns="False">
<DataGridTextColumn Header="One" Binding="{Binding PropOne}"/>
<DataGridTextColumn Header="Two" Binding="{Binding PropTwo}"/>
<DataGridComboBoxColumn Header="Three" ItemsSource="{Binding CollectionBindingTwo}"/>
</DataGrid>
For example, this works because ComboBox
is not inside a <DataGrid>
:
<ComboBox IsEditable="True" ItemsSource="{Binding CollectionBindingTwo}"></ComboBox>
The DataGridComboBoxColumn is not a part of the Visual Tree so the usual RelativeSource/ElementName binding formats won't work. You can use a workaround by defining the ElementStyle and EditingStyle where those binding formats will work. Another option is to use a BindingProxy which I use for other spots and will save some XAML when there is no other reason to define an ElementStyle/EditingStyle.
This is the BindingProxy class which inherits from Freezable.
public class BindingProxy : Freezable
{
#region Overrides of Freezable
protected override Freezable CreateInstanceCore()
{
return new BindingProxy();
}
#endregion
public object Data
{
get { return (object)GetValue(DataProperty); }
set { SetValue(DataProperty, value); }
}
// Using a DependencyProperty as the backing store for Data.
// This enables animation, styling, binding, etc...
public static readonly DependencyProperty DataProperty =
DependencyProperty.Register("Data",
typeof(object),
typeof(BindingProxy),
new UIPropertyMetadata(null));
}
Now your xaml looks like this:
<DataGrid DockPanel.Dock="Top"
ItemsSource="{Binding CollectionBindingOne}"
AutoGenerateColumns="False">
<DataGrid.Resources>
<helper:BindingProxy x:Key="proxy"
Data="{Binding }" />
</DataGrid.Resources>
<DataGrid.Columns>
<DataGridTextColumn Header="One"
Binding="{Binding PropOne}" />
<DataGridTextColumn Header="Two"
Binding="{Binding PropTwo}" />
<DataGridComboBoxColumn Header="Three"
ItemsSource="{Binding Data.CollectionBindingTwo,
Source={StaticResource proxy}}" />
</DataGrid>
Don't forget to declare the helper namespace import at the top of your Window/UserControl.
That's what the [RelativeSource][1]
bindings are for. In this case you should be able to target parent data context by way of the the DataGrid's data context:
<DataGrid>
<DataGridComboBoxColumn Header="Three" ItemsSource="{Binding
RelativeSource={RelativeSource AncestorType=DataGrid},
Path=DataContext.CollectionBindingTwo}" />
</DataGrid>
An ElementName
binding should also work:
<DataGrid x:Name="dataGrid">
<DataGridComboBoxColumn Header="Three"
ItemsSource="{Binding ElementName=dataGrid, Path=DataContext.CollectionBindingTwo}" />
</DataGrid>
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