WPF - Binding to current item from within group header style - wpf

Question

I'm something of a WPF noob so please take it easy on me ;-)
I am trying to create a grouped DataGrid (WPF toolkit version).
I have successfully created the data source, the DataGrid itself, the required CollectionViewSource and the Style for the group header (which uses an expander).
I want to group by a property called 'Assign_To' and have the relevant value (the value that the grouped items share) show up in the header. However, I cannot work out how to bind to the current group/item in order to return its Assign_To property.
The closest I have got (shown below) is binding to the overall CollectionViewSource, which returns a fixed value for Assign_To. What would be the proper way to bind to the current item/group in order to return the correct value for 'Assign_To'?
Hope someone can help. Thanks!
Andy T.
Here's the source...
<Window DataContext="{Binding Source={StaticResource SampleDataSource}}"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:dg="http://schemas.microsoft.com/wpf/2008/toolkit"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
x:Class="DataGridTest.MainWindow"
x:Name="Window"
Title="MainWindow"
Width="640" Height="480" mc:Ignorable="d">
<Window.Resources>
<CollectionViewSource x:Key="CVS" Source="{Binding MyData}">
<CollectionViewSource.GroupDescriptions>
<PropertyGroupDescription PropertyName="Assign_To"/>
</CollectionViewSource.GroupDescriptions>
</CollectionViewSource>
<Style x:Key="GroupHeaderStyle" TargetType="{x:Type GroupItem}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type GroupItem}">
<Expander IsExpanded="True">
<Expander.Header>
<StackPanel Orientation="Horizontal">
<TextBlock Text="Assign To: "/>
<TextBlock Text="{Binding Source={StaticResource CVS}, Path=Assign_To}"/>
</StackPanel>
</Expander.Header>
<ItemsPresenter/>
</Expander>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Window.Resources>
<Grid x:Name="LayoutRoot">
<dg:DataGrid
ItemsSource="{Binding Source={StaticResource CVS}}"
SelectionUnit="CellOrRowHeader"
CanUserAddRows="False"
CanUserDeleteRows="False"
CanUserResizeRows="False">
<dg:DataGrid.GroupStyle>
<GroupStyle ContainerStyle="{StaticResource GroupHeaderStyle}">
<GroupStyle.Panel>
<ItemsPanelTemplate>
<dg:DataGridRowsPresenter/>
</ItemsPanelTemplate>
</GroupStyle.Panel>
</GroupStyle>
</dg:DataGrid.GroupStyle>
</dg:DataGrid>
</Grid>
</Window>

Answer 1

Thanks for your reply. I really appreciate it and will check it out to see if it works.
Anyway, as it turns out, after some poking and prodding, I have worked it out using XAML only. What I had been missing was the fact that each item the group header is bound to is a GroupItem and that the default DataContext of a GroupItem is a CollectionViewGroup. In turn, a CollectionViewGroup has an Items property, which is a collection and I can therefore get the Assign_To value of the first item in the collection and use that in my header text. Like this:
<Style x:Key="GroupHeaderStyle" TargetType="{x:Type GroupItem}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type GroupItem}">
<Expander IsExpanded="True">
<Expander.Header>
<StackPanel Orientation="Horizontal">
<TextBlock Text="Assign To: "/>
<TextBlock Text="{Binding Items[0].Assign_To}"/>
</StackPanel>
</Expander.Header>
<ItemsPresenter/>
</Expander>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>

Answer 2

binding settings depend on the type of the Assign_To property. The simplest settings which could probably work for you would be:
<TextBlock Text="Assign To: "/>
<TextBlock Text="{Binding Name}"/>
pls, check if an example below would work for you; also this link WPF Toolkit DataGrid Part IV: TemplateColumns and Row Grouping might be helpful for you
code:
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
var dataProvider = (CollectionViewSource)FindResource("CVS");
dataProvider.Source = Test.GetTests();
}
}
public class Test
{
public string Assign_To { get; set; }
public string Test0 { get; set; }
public int Test1 { get; set; }
public static List<Test> GetTests()
{
List<Test> tests = new List<Test>();
tests.Add(new Test { Assign_To = "a", Test0 = "aaaa", Test1 = 1 });
tests.Add(new Test { Assign_To = "a", Test0 = "bbbb", Test1 = 1 });
tests.Add(new Test { Assign_To = "b", Test0 = "cccc", Test1 = 2 });
return tests;
}
}
xaml:
<Window.Resources>
<CollectionViewSource x:Key="CVS" >
<CollectionViewSource.GroupDescriptions>
<PropertyGroupDescription PropertyName="Assign_To"/>
</CollectionViewSource.GroupDescriptions>
</CollectionViewSource>
<Style x:Key="GroupHeaderStyle" TargetType="{x:Type GroupItem}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type GroupItem}">
<Expander IsExpanded="True">
<Expander.Header>
<StackPanel Orientation="Horizontal">
<TextBlock Text="Assign To: "/>
<TextBlock Text="{Binding Name}"/>
</StackPanel>
</Expander.Header>
<ItemsPresenter />
</Expander>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Window.Resources>
<Grid>
<DataGrid
ItemsSource="{Binding Source={StaticResource CVS}}"
HorizontalScrollBarVisibility="Hidden" SelectionMode="Extended"
AutoGenerateColumns="False"
Name="dataGrid1">
<DataGrid.GroupStyle>
<GroupStyle ContainerStyle="{StaticResource GroupHeaderStyle}">
<GroupStyle.Panel>
<ItemsPanelTemplate>
<DataGridRowsPresenter/>
</ItemsPanelTemplate>
</GroupStyle.Panel>
</GroupStyle>
</DataGrid.GroupStyle>
<DataGrid.Columns>
<DataGridTextColumn Header="Test0" Binding="{Binding Path=Test0}" />
<DataGridTextColumn Header="Test1" Binding="{Binding Path=Test1}" />
</DataGrid.Columns>
</DataGrid>
</Grid>