[WPF]ListView.SelectedItemsとListViewItem.IsSelectedの挙動を確認するテストプログラム

item.cs

using System;
using System.ComponentModel;
using System.Runtime.CompilerServices;

namespace WpfTraning
{
    public class Item : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        public string Name { get; private set; }

        bool _isSelected = false;
        public bool IsSelected
        {
            get { return _isSelected; }
            set
            {
                if (value == _isSelected)
                    return;
                _isSelected = value;
                if (this.PropertyChanged != null)
                    this.PropertyChanged(this, new PropertyChangedEventArgs("IsSelected"));
            }
        }

        public Item(string name)
        {
            this.Name = name;
        }
    }
    
    public class ViewModel
    {
        public ObservableCollection<Item> Items { get; private set; }

        public ViewModel()
        {
            this.Items = new ObservableCollection<Item>(
                from i in Enumerable.Range(0, 50) select new Item(i.ToString("d2"))
            );
        }
    }
}

MainWindow.xaml

<Window x:Class="WpfTraning.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:my="clr-namespace:WpfTraning"
        Height="300" Width="400">
    <Window.DataContext>
        <my:ViewModel/>
    </Window.DataContext>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition />
            <RowDefinition />
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition/>
            <ColumnDefinition/>
        </Grid.ColumnDefinitions>
        <ListView x:Name="lvw" ItemsSource="{Binding Items}">
            <ListView.View>
                <GridView>
                    <GridViewColumn Header="Name" DisplayMemberBinding="{Binding Name}" />
                </GridView>
            </ListView.View>
            <ListView.ItemContainerStyle>
                <Style TargetType="ListViewItem">
                    <Setter Property="IsSelected" Value="{Binding IsSelected}" />
                </Style>
            </ListView.ItemContainerStyle>
        </ListView>
        <ItemsControl Grid.Column="1" Grid.RowSpan="2" ItemsSource="{Binding Items}">
            <ItemsControl.ItemsPanel>
                <ItemsPanelTemplate>
                    <WrapPanel Margin="2" Orientation="Vertical" />
                </ItemsPanelTemplate>
            </ItemsControl.ItemsPanel>
            <ItemsControl.ItemTemplate>
                <DataTemplate>
                    <Border Margin="4">
                        <TextBlock Text="{Binding Name}" />
                        <Border.Style>
                            <Style TargetType="Border">
                                <Style.Triggers>
                                    <DataTrigger Binding="{Binding IsSelected}" Value="true">
                                        <Setter Property="Background"  Value="Orange" />
                                    </DataTrigger>
                                </Style.Triggers>
                            </Style>
                        </Border.Style>
                    </Border>
                </DataTemplate>
            </ItemsControl.ItemTemplate>
        </ItemsControl>
        <StackPanel Grid.Row="1">
            <StackPanel Orientation="Horizontal" Margin="5">
                <TextBlock Text="SelectedItems.Count:" />
                <TextBlock Text="{Binding ElementName=lvw, Path=SelectedItems.Count}" />
            </StackPanel>
            <StackPanel Orientation="Horizontal" Margin="5">
                <TextBox Name="textBoxName" Width="40" />
                <Button Name="ToggleSelection" Click="ToggleSelection_Click">Toggle selection</Button>
            </StackPanel>
        </StackPanel>
    </Grid>
</Window>

MainWindow.xaml.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Windows;

namespace WpfTraning
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void ToggleSelection_Click(object sender, RoutedEventArgs e)
        {
            foreach (var item in ((ViewModel)this.DataContext).Items.Where(x => x.Name == textBoxName.Text))
                item.IsSelected = !item.IsSelected;
        }
    }
}