what the name for the item in the green circle - wpf

Question

what's the element name in the green circle? Whta's the event corresponding to click this element?

Answer 1

Interestingly, this part of the DataGrid is no-man's-land - it doesn't even have an official name, let alone a behaviour or a template. In order to handle events related to this area, see here or here.

Answer 2

I call it the 'select all' button. However, it doesn't have an official name. It also does not have any style properties exposed. For a simple method to style it via attached properties, see the following:
http://www.scottlogic.co.uk/blog/colin/2009/02/styling-hard-to-reach-elements-in-control-templates-with-attached-behaviours/
Colin E.

Answer 3

As others have stated, it's the "Select All" Button. Clicking it will select everything in the DataGrid if SelectionMode is set to Extended.
The "Select All" Button is part of the DataGrid Template. Or actually, it's part of the ScrollViewer Template that is part of the DataGrid Template so it's nested pretty deep. The ControlTemplate looks like this. From here you can do anything you want with the SelectAll Button, disable it, change the Background etc.
<Style TargetType="{x:Type DataGrid}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type DataGrid}">
<Border BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Padding="{TemplateBinding Padding}" SnapsToDevicePixels="True">
<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>
<!-- Here it is -->
<Button Command="{x:Static DataGrid.SelectAllCommand}" Focusable="false" Style="{DynamicResource {ComponentResourceKey ResourceId=DataGridSelectAllButtonStyle, TypeInTargetAssembly={x:Type DataGrid}}}" Visibility="{Binding HeadersVisibility, ConverterParameter={x:Static DataGridHeadersVisibility.All}, Converter={x:Static DataGrid.HeadersVisibilityConverter}, RelativeSource={RelativeSource AncestorType={x:Type DataGrid}}}" Width="{Binding CellsPanelHorizontalOffset, RelativeSource={RelativeSource AncestorType={x:Type DataGrid}}}"/>
<DataGridColumnHeadersPresenter x:Name="PART_ColumnHeadersPresenter" Grid.Column="1" Visibility="{Binding HeadersVisibility, ConverterParameter={x:Static DataGridHeadersVisibility.Column}, Converter={x:Static DataGrid.HeadersVisibilityConverter}, RelativeSource={RelativeSource AncestorType={x:Type DataGrid}}}"/>
<ScrollContentPresenter x:Name="PART_ScrollContentPresenter" CanContentScroll="{TemplateBinding CanContentScroll}" Grid.ColumnSpan="2" Grid.Row="1"/>
<ScrollBar x:Name="PART_VerticalScrollBar" Grid.Column="2" Maximum="{TemplateBinding ScrollableHeight}" Orientation="Vertical" Grid.Row="1" Visibility="{TemplateBinding ComputedVerticalScrollBarVisibility}" Value="{Binding VerticalOffset, Mode=OneWay, RelativeSource={RelativeSource TemplatedParent}}" ViewportSize="{TemplateBinding ViewportHeight}"/>
<Grid Grid.Column="1" Grid.Row="2">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="{Binding NonFrozenColumnsViewportHorizontalOffset, RelativeSource={RelativeSource AncestorType={x:Type DataGrid}}}"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<ScrollBar x:Name="PART_HorizontalScrollBar" Grid.Column="1" Maximum="{TemplateBinding ScrollableWidth}" Orientation="Horizontal" Visibility="{TemplateBinding ComputedHorizontalScrollBarVisibility}" Value="{Binding HorizontalOffset, Mode=OneWay, RelativeSource={RelativeSource TemplatedParent}}" ViewportSize="{TemplateBinding ViewportWidth}"/>
</Grid>
</Grid>
</ControlTemplate>
</ScrollViewer.Template>
<ItemsPresenter SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
</ScrollViewer>
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>

Answer 4

If you want to disable the selectall button you can also do like this:
//Disable select all button
datagrid.CommandBindings.Add(new CommandBinding(DataGrid.SelectAllCommand, delegate { }, (s, a) => { if (a.OriginalSource is Button) ((Button)a.OriginalSource).IsEnabled = false; }));
as a workaround.
This can also be used to wire other things up.
The "problem" with re-templating is that you have to take all the themes into account... tedious :)

Answer 5

In at least one example I found, clicking the gray triangle in the corner causes all rows to be selected.
But this is not a built-in feature of this control as far as I know. It is part of a custom template.
See this example:
http://www.dotnetspark.com/kb/2941-styling-wpf-datagrid.aspx
If you download the sample, and search the Resources/DataGridCustomization.xaml file for "SelectAll", you'll find the part of the template that contains this feature.