DataGrid custom CanUserAddRows implementation - wpf

Question

I want to implement a custom add row button to a DataGrid (it's a long story). I added the button in template, and define an attached property, and I can get the button's click. But I can not add a new row in a generic way -not for a specified type-. I know that I can do similar thing in ViewModel, but I'm looking to do this in templates and attached properties. Here is my try; Any idea to complete this?
XAML:
<Style x:Key="{x:Type DataGrid}" TargetType="{x:Type DataGrid}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type DataGrid}">
<Border x:Name="border">
<ScrollViewer x:Name="DG_ScrollViewer" Focusable="false">
<ScrollViewer.Template>
<ControlTemplate TargetType="{x:Type ScrollViewer}">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="Auto" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="*" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<Button Focusable="false"
Command="{x:Static DataGrid.SelectAllCommand}" />
<DataGridColumnHeadersPresenter
x:Name="PART_ColumnHeadersPresenter"
Grid.Column="1" />
<Grid Grid.ColumnSpan="2" Grid.Row="1">
<Grid.RowDefinitions>
<RowDefinition Height="*"/>
<RowDefinition Height="22" />
</Grid.RowDefinitions>
<ScrollContentPresenter
x:Name="PART_ScrollContentPresenter" />
<!-- THIS IS MY CUSTOM BUTTON TO ADD NEW ROW -->
<Button x:Name="PART_AddRowButton"
Content="Add"/>
</Grid>
<ScrollBar x:Name="PART_VerticalScrollBar"/>
<Grid Grid.Column="1" Grid.Row="2">
<ScrollBar x:Name="PART_HorizontalScrollBar"/>
</Grid>
</Grid>
</ControlTemplate>
</ScrollViewer.Template>
<ItemsPresenter SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" />
</ScrollViewer>
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
C#:
public class DataGridHelper {
public static readonly DependencyProperty CanUserAddRowsProperty
= DependencyProperty.RegisterAttached(
"CanUserAddRows", typeof(bool), typeof(DataGridHelper),
new FrameworkPropertyMetadata(default(bool), CanUserAddRowsChanged));
[AttachedPropertyBrowsableForType(typeof(DataGrid))]
public static bool GetCanUserAddRows(DependencyObject obj) {
return (bool)obj.GetValue(CanUserAddRowsProperty);
}
[AttachedPropertyBrowsableForType(typeof(DataGrid))]
public static void SetCanUserAddRows(DependencyObject obj, bool value) {
obj.SetValue(CanUserAddRowsProperty, value);
}
private static void CanUserAddRowsChanged(
DependencyObject d,
DependencyPropertyChangedEventArgs e) {
var dataGrid = d as DataGrid;
if (dataGrid == null)
return;
bool oldValue = (bool)e.OldValue,
newValue = (bool)e.NewValue;
if (newValue == oldValue)
return;
if (newValue) {
dataGrid.Loaded += CanUserAddRowsDataGridLoaded;
} else {
dataGrid.Loaded -= CanUserAddRowsDataGridLoaded;
}
}
private static void CanUserAddRowsDataGridLoaded(object sender, RoutedEventArgs e) {
var dataGrid = sender as DataGrid;
if (dataGrid == null)
return;
if (dataGrid.Style == null)
return;
var rootTemplate = dataGrid.Template;
if (rootTemplate == null)
return;
var scroll = rootTemplate.FindName("DG_ScrollViewer", dataGrid) as ScrollViewer;
if (scroll == null)
return;
var scrollTemplate = scroll.Template;
if (scrollTemplate == null)
return;
var button = scrollTemplate.FindName("PART_AddRowButton", scroll) as ButtonBase;
if (button == null)
return;
if (GetCanUserAddRows(dataGrid)) {
button.Click += AddRowClicked;
} else {
button.Click -= AddRowClicked;
}
}
private static void AddRowClicked(object sender, RoutedEventArgs e) {
var button = ((ButtonBase)sender);
var parent = VisualTreeHelper.GetParent(button);
while (!(parent is DataGrid))
parent = VisualTreeHelper.GetParent(parent);
var source = ((DataGrid)parent).Items.Add(...) // now what???
}
}
Well, as you can see, I got access to DataGrid after button got clicked; But what is next? How can I force the DataGrid to show NewItemPlaceHolder?

Answer 1

Typically in WPF, we bind collections (preferably collections that support change notification like ObservableCollection) of data objects to UI controls. Rather than adding new items to the UI controls, we add the items to the collections in the code behind/view model. As long as the collection support change notification, the UI controls will be automatically updated.
So to add a new row to your DataGrid, you need to add a new item to your collection:
dataCollection.Add(new DataType());
You should be able to access your data bound collection in your AttachedProperty using:
var dataCollection = (DataCollectionType)dataGrid.ItemsSource;
I believe that you can also use:
dataGrid.Items.Add(new DataType());
although this method is not recommended.