In a WPF Project I have some restyled DataGridColumnHeaders
of a DataGrid
which show a ComboBox
for each DataGridColumnHeader
. When the user selects from the ComboBox
's the SelectionChanged
handler (in the code behind) updates an Array
of ColumnOptionViewModel
objects on the MainWindowViewModel
with the newest selection.
At this point some code also works out if there are any duplicate selections in this array, and then sets an IsDuplicate
Boolean property on the ColumnOptionViewModel
that are duplicates. The idea is that a DataTrigger
picks up the change in IsDuplicate
and changes the Background
of a TextBlock
in the DataTemplate
of the ItemTemplate
for the duplicate ComboBox
's to Red
.
However, this trigger is not firing. The IsDuplicate
properties are being set ok, and everything else works as expected. What am I doing wrong?
Here is the XAML for the Window:
<Window x:Class="TestDataGrid.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:TestDataGrid"
mc:Ignorable="d"
Title="MainWindow" Height="350" Width="525">
<Grid>
<DataGrid Grid.Row="1" x:Name="dataGrid" ItemsSource="{Binding Records}">
<DataGrid.ColumnHeaderStyle>
<Style TargetType="DataGridColumnHeader">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate>
<StackPanel>
<ComboBox x:Name="cbo"
ItemsSource="{Binding RelativeSource={RelativeSource AncestorType={x:Type DataGrid}},Path=DataContext.ColumnOptions}"
SelectionChanged="cbo_SelectionChanged">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock x:Name="txt" Text="{Binding Name}"/>
<DataTemplate.Triggers>
<DataTrigger Binding="{Binding ElementName=cbo, Path=SelectedItem.IsDuplicate}">
<Setter TargetName="txt" Property="Background" Value="Red"/>
</DataTrigger>
</DataTemplate.Triggers>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
</StackPanel>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</DataGrid.ColumnHeaderStyle>
</DataGrid>
</Grid>
CODE BEHIND:
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
this.DataContext = new MainWindowViewModel(RecordProvider.GetRecords());
}
private void cbo_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
var vm = (MainWindowViewModel)DataContext;
var selectionChangedCombo = (ComboBox)e.Source;
var dataGridColumnHeader = selectionChangedCombo.TemplatedParent as DataGridColumnHeader;
vm.ColumnSelections[dataGridColumnHeader.DisplayIndex] = selectionChangedCombo.SelectedItem as ColumnOptionViewModel;
CheckForDuplicates();
}
private void CheckForDuplicates()
{
var vm = (MainWindowViewModel)DataContext;
var duplicates = vm.ColumnSelections.GroupBy(x => x.Name)
.Where(g => g.Skip(1).Any())
.SelectMany(g => g);
foreach (var option in duplicates)
{
option.IsDuplicate = true;
}
}
}
MainWindowViewModel :
public class MainWindowViewModel : ViewModelBase
{
public ObservableCollection<ColumnOptionViewModel> _columnOptions = new ObservableCollection<ColumnOptionViewModel>();
public ObservableCollection<RecordViewModel> _records = new ObservableCollection<RecordViewModel>();
ColumnOptionViewModel[] _columnSelections = new ColumnOptionViewModel[3];
public MainWindowViewModel(IEnumerable<Record> records)
{
foreach (var rec in records)
{
Records.Add(new RecordViewModel(rec));
}
ColumnOptions.Add(new ColumnOptionViewModel(TestDataGrid.ColumnOptions.ColumnOption1));
ColumnOptions.Add(new ColumnOptionViewModel(TestDataGrid.ColumnOptions.ColumnOption2));
ColumnOptions.Add(new ColumnOptionViewModel(TestDataGrid.ColumnOptions.ColumnOption3));
ColumnSelections[0] = ColumnOptions[0];
ColumnSelections[1] = ColumnOptions[1];
ColumnSelections[2] = ColumnOptions[2];
}
public ObservableCollection<ColumnOptionViewModel> ColumnOptions
{
get { return _columnOptions; }
set { _columnOptions = value; }
}
public ColumnOptionViewModel[] ColumnSelections
{
get { return _columnSelections; }
set { _columnSelections = value; }
}
public ObservableCollection<RecordViewModel> Records
{
get { return _records; }
set { _records = value; }
}
}
ColumnOptionViewModel :
public class ColumnOptionViewModel : ViewModelBase
{
ColumnOptions _colOption;
public ColumnOptionViewModel(ColumnOptions colOption )
{
_colOption = colOption;
}
public string Name
{
get { return _colOption.ToString(); }
}
public override string ToString()
{
return Name;
}
private bool _isDuplicate = false;
public bool IsDuplicate
{
get { return _isDuplicate; }
set
{ _isDuplicate = value;
OnPropertyChanged();
}
}
}
EDIT:
ViewModelBase :
public abstract class ViewModelBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
If you are trying to bind to the IsDuplicate
property of the SelectedItem
in the ComboBox
you could use a RelativeSource
.
You should also set the Value
property of the DataTrigger
to true/false depending on when you want the Background
property of the TextBlock
to be set to Red
:
<ComboBox x:Name="cbo" ItemsSource="{Binding RelativeSource={RelativeSource AncestorType={x:Type DataGrid}},Path=DataContext.ColumnOptions}"
SelectionChanged="cbo_SelectionChanged">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock x:Name="txt" Text="{Binding Name}"/>
<DataTemplate.Triggers>
<DataTrigger Binding="{Binding Path=SelectedItem.IsDuplicate, RelativeSource={RelativeSource AncestorType=ComboBox}}" Value="True">
<Setter TargetName="txt" Property="Background" Value="Red"/>
</DataTrigger>
</DataTemplate.Triggers>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>