WPF DataGridの行をフィルタリングする

<Window x:Class="WpfDataGridFiltering.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:WpfDataGridFiltering"
        mc:Ignorable="d"
        Title="FilteringRecords" Height="300" Width="400">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <GroupBox Header="性別選択">
            <StackPanel Orientation="Horizontal">
                <RadioButton x:Name="radioAll" Content="全て" GroupName="genderFilter" Margin="0,4,8,0" IsChecked="True" Checked="OnRadioAllChecked"/>
                <RadioButton x:Name="radioMen" Content="男性" GroupName="genderFilter" Margin="0,4,8,0" Checked="OnRadioMenChecked"/>
                <RadioButton x:Name="radioWomen" Content="女性" GroupName="genderFilter" Margin="0,4,8,0" Checked="OnRadioWomenChecked"/>
            </StackPanel>
        </GroupBox>
        <DataGrid x:Name="Dg"
                  Grid.Row="1"
                  SelectionMode="Single"
                  HeadersVisibility="Column"
                  SelectionUnit="Cell"
                  AutoGenerateColumns="False"
                  CanUserAddRows="False"
                  Margin="0,10,0,0">
            <DataGrid.Columns>
                <DataGridTextColumn Header="番号" Binding="{Binding number}" IsReadOnly="True" Width="50" CanUserSort="False"/>
                <DataGridTextColumn Header="名前" Binding="{Binding name}" IsReadOnly="True" Width="*" CanUserSort="False"/>
                <DataGridTextColumn Header="年齢" Binding="{Binding age}" IsReadOnly="True" Width="60" CanUserSort="False"/>
                <DataGridTextColumn Header="性別" Binding="{Binding gender}" IsReadOnly="True" Width="60" CanUserSort="False"/>
            </DataGrid.Columns>
        </DataGrid>
    </Grid>
</Window>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.ComponentModel;
using System.Collections.ObjectModel;

namespace WpfDataGridFiltering
{
    /// <summary>
    /// MainWindow.xaml の相互作用ロジック
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            GridRecords.Add(new GridRecord { number = 1, name = "山田 太郎", age = 28, gender = "男" });
            GridRecords.Add(new GridRecord { number = 2, name = "立花 薫", age = 48, gender = "男" });
            GridRecords.Add(new GridRecord { number = 3, name = "鈴木 花子", age = 32, gender = "女" });
            GridRecords.Add(new GridRecord { number = 4, name = "原田 尚美", age = 26, gender = "女" });
            GridRecords.Add(new GridRecord { number = 5, name = "吉川 雅之", age = 21, gender = "男" });
            GridRecords.Add(new GridRecord { number = 6, name = "寺尾 友紀", age = 50, gender = "女" });
            GridRecords.Add(new GridRecord { number = 7, name = "高橋 寛之", age = 33, gender = "男" });

            collectionView = CollectionViewSource.GetDefaultView(GridRecords);

            collectionView.Filter = new Predicate<object>(target =>
            {
                GridRecord gridRecord = target as GridRecord;

                if(gridRecord != null)
                {
                    if(selectGender == SelectedGender.ALL)
                    {
                        return true;
                    } 
                    else if(selectGender == SelectedGender.Men && gridRecord.gender == MEN)
                    {
                        return true;
                    }
                    else if(selectGender == SelectedGender.Women && gridRecord.gender == WOMEN)
                    {
                        return true;
                    }
                    else
                    {
                        return false;
                    }
                }
                return true;
            });

            Dg.ItemsSource = collectionView;
        }

        public class GridRecord
        {
            public int number { get; set; }
            public string name { get; set; }
            public int age { get; set; }
            public string gender { get; set; }
        }

        private ObservableCollection<GridRecord> GridRecords = new ObservableCollection<GridRecord>();

        private ICollectionView collectionView;

        private enum SelectedGender
        {
            ALL = 0,
            Men,
            Women
        }

        private const string MEN = "男";
        private const string WOMEN = "女";

        private SelectedGender selectGender = SelectedGender.ALL;

        private void OnRadioAllChecked(object sender, RoutedEventArgs e)
        {
            selectGender = SelectedGender.ALL;
            collectionView?.Refresh();
        }

        private void OnRadioMenChecked(object sender, RoutedEventArgs e)
        {
            selectGender = SelectedGender.Men;
            collectionView?.Refresh();
        }

        private void OnRadioWomenChecked(object sender, RoutedEventArgs e)
        {
            selectGender = SelectedGender.Women;
            collectionView?.Refresh();
        }
    }
}