ListViewにおいて複数選択したアイテムを、コードビハインドを使わずに取得したい。

質問

ListViewにおいて複数選択した場合に、コードビハインドを使わずにアイテム群を取得したいです。
ビヘイビアを使用して取得しようと試みているのですが、複数選択した場合でも、
以下のコード内の「SelectedStudents」にアイテム群が入らずにnullのままです。
原因を教えていただけますようよろしくお願いいたします。

BM_StudentList.xaml(一部抜粋)

C#
1<UserControl x:Class="Presentation.BillingManagement.BM_StudentList"
2             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
3             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
4             xmlns:i="http://schemas.microsoft.com/xaml/behaviors"
5             xmlns:prism="http://prismlibrary.com/" 
6             xmlns:local="clr-namespace:Presentation.BillingManagement"
7             prism:ViewModelLocator.AutoWireViewModel="True">
8    <StackPanel  Margin="10" >
9        <ListView ItemsSource="{Binding Students}"
10            Width="Auto" HorizontalContentAlignment="Stretch">
11            <i:Interaction.Behaviors>
12                <local:SelectedItemsBehavior SelectedItems="{Binding SelectedStudents}" />
13            </i:Interaction.Behaviors>
14            <ListView.View >
15                <GridView  >
16                    <GridViewColumn Header="番号" DisplayMemberBinding="{Binding Id}" Width="50"/>
17                    <GridViewColumn Header="氏名" DisplayMemberBinding="{Binding Name}" Width="Auto" />
18                    <GridViewColumn Header="ﾌﾘｶﾞﾅ" DisplayMemberBinding="{Binding Kana}" Width="Auto" />
19                </GridView>
20            </ListView.View>
21        </ListView>
22        <Button Content="読込" Command="{Binding OkButton}" 
23                HorizontalAlignment="Right" Width="60"  Margin="10"/>
24    </StackPanel>
25</UserControl>

BM_StudentListViewModel.cs(一部抜粋)

C#
1using Prism.Commands;
2using Prism.Mvvm;
3using Prism.Services.Dialogs;
4using System;
5using System.Collections.ObjectModel;
6
7namespace Presentation.BillingManagement
8{
9    public class BM_StudentListViewModel : BindableBase, IDialogAware
10    {
11        private StudentUsecase _usecase;
12        public BM_StudentListViewModel(StudentUsecase usecase)
13        {
14            _usecase = usecase;
15            Students = _usecase.GetStudents();
16            OkButton = new DelegateCommand(OkButtonExecute);
17        }
18
19        private ObservableCollection<Student> _students
20                = new ObservableCollection<Student>();
21        public ObservableCollection<Student> Students
22        {
23            get { return _students; }
24            set { SetProperty(ref _students, value); }
25        }
26
27        private ObservableCollection<Student> _selectedStudents;
28        public ObservableCollection<Student> SelectedStudents
29        {
30            get { return _selectedStudents; }
31            set { SetProperty(ref _selectedStudents, value); }
32        }
33
34        public DelegateCommand OkButton { get; }
35        private void OkButtonExecute()
36        {
37            var r = ButtonResult.OK;
38            if (SelectedStudents == null)
39            {
40                r = ButtonResult.None;
41            }
42            var p = new DialogParameters();
43            p.Add(nameof(SelectedStudents), SelectedStudents);
44            RequestClose.Invoke(new DialogResult(r, p));
45        }
46    }
47}
48

BM_Behavior.cs

C#
1using Microsoft.Xaml.Behaviors;
2using System.Collections;
3using System.Linq;
4using System.Windows;
5using System.Windows.Controls;
6using System.Windows.Controls.Primitives;
7
8namespace Presentation.BillingManagement
9{
10    [TypeConstraint(typeof(Selector))]
11    public class SelectedItemsBehavior : Behavior<Selector>
12    {
13        public static readonly DependencyProperty SelectedItemsProperty =
14            DependencyProperty.Register("SelectedItems",
15                                        typeof(IEnumerable),
16                                        typeof(SelectedItemsBehavior),
17                new FrameworkPropertyMetadata(null,
18                    FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));
19        public IEnumerable SelectedItems
20        {
21            get => (IEnumerable)GetValue(SelectedItemsProperty);
22            set => SetValue(SelectedItemsProperty, value);
23        }
24        protected override void OnAttached()
25        {
26            base.OnAttached();
27            AssociatedObject.SelectionChanged += SelectionChanged;
28        }
29        protected override void OnDetaching()
30        {
31            AssociatedObject.SelectionChanged -= SelectionChanged;
32            base.OnDetaching();
33        }
34        private void SelectionChanged(object sender, SelectionChangedEventArgs args)
35        {
36            dynamic selector = AssociatedObject;
37            SelectedItems = Enumerable.ToArray(selector.SelectedItems);
38        }
39    }
40}

補足情報

C#
WPF
Prism.Unity
Prism.Wpf
Microsoft.Xaml.Behaviors.Wpf
を使用しています。

行動規範の内容に同意します

回答1件

ベストアンサー

参考コードがある場合は、質問に明示してください。
(WPF) SelectedItems をViewModelで取得する - まめ - たんたんめん

以下のコード内の「SelectedStudents」にアイテム群が入らずにnullのままです。

SelectedItemsBehaviorでは、SelectedItemsがIEnumerableと定義されています（実体はobject[]です）
ObservableCollection<Student>にはキャストできませんのでnullになります。

ViewModel側もそれに合わせてIEnumerableとする必要があります。

そもそもこのビヘイビアは選択が変わるたびに、SelectedItemsが丸ごと入れ替わります。
そのためObservableCollectionの意味はありません。

そしてこのコードではViewでの変更しか感知できません（TwoWay指定になっていますが^^;

xml
1<Window
2  x:Class="Questions351149.MainWindow"
3  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
4  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
5  xmlns:i="http://schemas.microsoft.com/xaml/behaviors"
6  xmlns:local="clr-namespace:Questions351149"
7  Width="800"
8  Height="450">
9  <Window.DataContext>
10    <local:BM_StudentListViewModel />
11  </Window.DataContext>
12  <DockPanel Margin="10">
13    <Button
14      MinWidth="60"
15      Margin="10"
16      HorizontalAlignment="Right"
17      Command="{Binding OkButton}"
18      Content="読込"
19      DockPanel.Dock="Bottom" />
20
21    <ListView ItemsSource="{Binding Students}" SelectionMode="Multiple">
22      <i:Interaction.Behaviors>
23        <local:SelectedItemsBehavior SelectedItems="{Binding SelectedStudents}" />
24      </i:Interaction.Behaviors>
25      <ListView.View>
26        <GridView>
27          <GridViewColumn DisplayMemberBinding="{Binding Id}" Header="番号" />
28          <GridViewColumn DisplayMemberBinding="{Binding Name}" Header="氏名" />
29          <GridViewColumn DisplayMemberBinding="{Binding Kana}" Header="ﾌﾘｶﾞﾅ" />
30        </GridView>
31      </ListView.View>
32    </ListView>
33  </DockPanel>
34</Window>

cs
1using Microsoft.Xaml.Behaviors;
2using Prism.Commands;
3using Prism.Mvvm;
4using System.Collections;
5using System.Collections.ObjectModel;
6using System.Diagnostics;
7using System.Linq;
8using System.Windows;
9using System.Windows.Controls;
10using System.Windows.Controls.Primitives;
11
12namespace Questions351149
13{
14    [TypeConstraint(typeof(Selector))]
15    public class SelectedItemsBehavior : Behavior<Selector>
16    {
17        public static readonly DependencyProperty SelectedItemsProperty =
18            DependencyProperty.Register(nameof(SelectedItems),
19                                        typeof(IEnumerable),
20                                        typeof(SelectedItemsBehavior),
21                new FrameworkPropertyMetadata(null,
22                    FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));
23        public IEnumerable SelectedItems
24        {
25            get => (IEnumerable)GetValue(SelectedItemsProperty);
26            set => SetValue(SelectedItemsProperty, value);
27        }
28        protected override void OnAttached()
29        {
30            base.OnAttached();
31            AssociatedObject.SelectionChanged += SelectionChanged;
32        }
33        protected override void OnDetaching()
34        {
35            AssociatedObject.SelectionChanged -= SelectionChanged;
36            base.OnDetaching();
37        }
38        private void SelectionChanged(object sender, SelectionChangedEventArgs args)
39        {
40            dynamic selector = AssociatedObject;
41            SelectedItems = Enumerable.ToArray(selector.SelectedItems);
42        }
43    }
44
45    public class BM_StudentListViewModel : BindableBase
46    {
47        public ObservableCollection<Student> Students { get; }
48
49        private IEnumerable _selectedStudents;
50        public IEnumerable SelectedStudents
51        {
52            get => _selectedStudents;
53            set => SetProperty(ref _selectedStudents, value);
54        }
55
56        public DelegateCommand OkButton { get; }
57
58
59        public BM_StudentListViewModel()
60        {
61            Students = new ObservableCollection<Student>(Enumerable.Range(0, 50).Select(_ => new Student()));
62            OkButton = new DelegateCommand(OkButtonExecute);
63        }
64
65        private void OkButtonExecute()
66        {
67            if (SelectedStudents == null) return;
68            foreach (Student s in SelectedStudents)
69            {
70                Debug.WriteLine(s);
71            }
72            Debug.WriteLine("");
73        }
74    }
75
76    public class Student
77    {
78        public string Id { get; }
79        public string Name { get; }
80        public string Kana { get; }
81
82        private static int no;
83        public Student()
84        {
85            Id = $"Id{++no}";
86            Name = $"Name{no}";
87            Kana = $"Kana{no}";
88        }
89
90        public override string ToString() => $"Id:{Id}, Name:{Name}, Kana:{Kana}";
91    }
92
93    public partial class MainWindow : Window
94    {
95        public MainWindow() => InitializeComponent();
96    }
97}