Select DataGrid items in particular group using checkbox/button in group header

Environment

Product Version	2020.3.1106.1
Product	DataGrid for Xamarin.Forms

Description

This help article will show you how to select att items inside a particular group using checkbox/button inside the group header template. This is a custom scenario which uses the DataGird groupheader template.

Solution

We can use the normal DataGrid selection mechanism.

The specific here is that you need to find which items are in the group and select them. This can be accomplished by using the DataGrid's DataView.

var dataView = MyDataGrid.GetDataView();

You can traverse the groups and get the ChildItems in any particular group. With references to the items, you can programmatically select them.

Example select all items from group using button

Here's a DataGrid bound to a list of People and grouped by Gender property,

<dataGrid:RadDataGrid x:Name="DataGrid" ItemsSource="{Binding People}" SelectionUnit="Row" SelectionMode="Multiple">
    <dataGrid:RadDataGrid.GroupDescriptors>
        <data:PropertyGroupDescriptor PropertyName="Gender"/>
    </dataGrid:RadDataGrid.GroupDescriptors>
</dataGrid:RadDataGrid>

You can use the DataView to get a list of the groups, then find the group for Male and select the items in the Male group:

private void Button_Clicked(object sender, EventArgs e)
{
    // Get the DataView.
    var dataView = DataGrid.GetDataView();

    // Get all the groups in the DataView.
    var groups = dataView.GetGroups();

    // Get the group you want to make the selections in.
    var maleGroup = groups.FirstOrDefault(g => g.Key.ToString() == "Male");

    // Select all the rows in that group.
    foreach (var item in maleGroup.ChildItems)
    {
        DataGrid.SelectItem(item);
    }
}

Example select all items from a group using a CheckBox

Customizing GroupHeaderTemplate

For this, you'll need to override the default header template and implement a completely custom one. When creating a GroupHeaderTemplate, you'll want to keep in mind that the BindingContext is a GroupHeaderContext object. This contains useful information, such as Group, Descriptor, etc.

For a "Select All" checkbox, the header template will need an extra UI element, here's an example with RadCheckBox

<dataGrid:RadDataGrid.GroupHeaderTemplate>
    <DataTemplate>
        <StackLayout Orientation="Horizontal">
            <Label Text="{Binding Group.Key}" FontAttributes="Bold" VerticalOptions="Center" Margin="0,0,10,0"/>
            <primitives:RadCheckBox IsCheckedChanged="GroupHeaderCheckbox_OnIsCheckedChanged" VerticalOptions="Center" />
            <Label Text="Select All" VerticalOptions="Center" />
        </StackLayout>
    </DataTemplate>
</dataGrid:RadDataGrid.GroupHeaderTemplate>

The checkbox's IsCheckedChanged event handler is going to need to either select all or deselect all based on the value of the RadCheckBox:

private void GroupHeaderCheckbox_OnIsCheckedChanged(object sender, Telerik.XamarinForms.Primitives.CheckBox.IsCheckedChangedEventArgs e)
{
    if(sender is RadCheckBox cb && cb.BindingContext is GroupHeaderContext context)
    {
        foreach (var item in context.Group.ChildItems)
        {
            if (e.NewValue == true)
            {
                context.Grid.SelectItem(item);
            }
            else
            {
                context.Grid.DeselectItem(item);
            }
        }
    }
}