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How to show multi grouped grid's inner child items count in main parent group header on rad data grid

Environment

Product Version 2020.3.1207.1
Product DataGrid for Xamarin.Forms

Description

The following how-to article will show you how to visualize the children's items count of the inner group inside the outer group. For this purpose, we will use the DataGrid GroupHeaderTemplate.

Solution

We will need to implement a converter to get the inner group children's items count. Create a class for example MyConverter:

public class MyConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {

        var groupHeaderContext = value as GroupHeaderContext;
        if (groupHeaderContext != null)
        {
            var group = groupHeaderContext.Group;
            if (group != null)
            {
                var totalItemsCount = this.GetTotalChildrenCount(group);
                return "Total child items count: " + totalItemsCount;
            }
        }

        return string.Empty;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
    private int GetTotalChildrenCount(IDataGroup group)
    {
        int count = 0;
        foreach (var item in group.ChildItems)
        {
            var childGroup = item as IDataGroup;
            if (childGroup != null)
            {
                count += this.GetTotalChildrenCount(childGroup);
            }
            else
            {
                count++;
            }
        }

        return count;
    }
}

you will need the following namespace for the GroupHHeaderContext:

using Telerik.XamarinForms.Common.Data;
using Telerik.XamarinForms.DataGrid;

Here is the used business model and ViewModel:

public class Country
{
    public string Name { get; set; }
    public string Region { get; set; }
    public string SalesName { get; set; }
}
public class ViewModel
{
    public ViewModel()
    {
        this.Items = new ObservableCollection<Country>
        {
            new Country{Name ="Australia", Region="East", SalesName="Camra" },
            new Country{Name ="Australia", Region="East", SalesName="Camba" },
            new Country{Name ="Australia", Region="West", SalesName="bera" },
            new Country{Name ="Australia", Region="South", SalesName="C" },
            new Country{Name ="Australia", Region="Center", SalesName="C" },
            new Country{Name ="UK", Region="East", SalesName = "Cate" },
            new Country{Name ="UK", Region="West", SalesName = "Jack" },
            new Country{Name ="UK", Region="Center", SalesName="James" },
            new Country{Name ="USA", Region="East", SalesName="John" },
            new Country{Name ="USA", Region="East", SalesName="Doe" },
            new Country{Name ="USA", Region="East", SalesName="Katelin" },
            new Country{Name ="USA", Region="West", SalesName="Joan" },
            new Country{Name ="USA", Region="South", SalesName="Amanda" },
            new Country{Name ="USA", Region="North", SalesName="Daniel" },
            new Country{Name ="USA", Region="South", SalesName="Amanda" },
        };
    }

    public ObservableCollection<Country> Items { get; set; }
}

And finaly this is the DataGrid definition and how the GroupHeaderTemplate is defined:

<telerikDataGrid:RadDataGrid x:Name="dataGrid"
                                ItemsSource="{Binding Items}"
                                AutoGenerateColumns="false"
                                DataOperationIndicationMode="Universal"
                                GridLinesColor="#DDE0E3"
                                GridLinesVisibility="Both">
    <telerikDataGrid:RadDataGrid.GroupHeaderTemplate>
        <DataTemplate>
            <StackLayout Orientation="Horizontal" 
                        Margin="5,0,0,0" 
                        VerticalOptions="Center" >
                <Label Text="{Binding Group.Key}" 
                    FontAttributes="Bold" 
                    TextColor="DarkCyan" 
                    FontSize="Small" />
                <Label Text="{Binding Group.Items.Count}" 
                    FontAttributes="Bold" 
                    TextColor="DarkCyan" 
                    FontSize="Small" />
                <Label Text="{Binding ., Converter={StaticResource myConverter}}" 
                    FontAttributes="Bold" 
                    TextColor="Red" 
                    FontSize="16" />
            </StackLayout>
        </DataTemplate>
    </telerikDataGrid:RadDataGrid.GroupHeaderTemplate>
    <telerikDataGrid:RadDataGrid.GroupDescriptors>
        <common:PropertyGroupDescriptor PropertyName="Name"/>
        <common:PropertyGroupDescriptor PropertyName="Region"/>
    </telerikDataGrid:RadDataGrid.GroupDescriptors>

    <telerikDataGrid:RadDataGrid.Columns>
        <telerikDataGrid:DataGridTextColumn PropertyName="SalesName" HeaderText="Sales">
        </telerikDataGrid:DataGridTextColumn>
    </telerikDataGrid:RadDataGrid.Columns>
</telerikDataGrid:RadDataGrid>

Register the converter inside the Page's Resources:

<ContentPage.Resources>
    <ResourceDictionary>
        <local:MyConverter x:Key="myConverter"/>
    </ResourceDictionary>
</ContentPage.Resources>

also you will need the following namespaces:

xmlns:telerikDataGrid="clr-namespace:Telerik.XamarinForms.DataGrid;assembly=Telerik.XamarinForms.DataGrid" 
xmlns:common="clr-namespace:Telerik.XamarinForms.Common.Data;assembly=Telerik.XamarinForms.Common"
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