标签：SelectedItems System IList new using WPF ListBox public
ListBox的SelectedItems属性是只读属性，没法直接绑定。
一般的处理方式是在命令中通过命令参数传递到ViewModel里面。
现在通过附加属性来解决这个问题
效果
后台代码
1 using Microsoft.Toolkit.Mvvm.ComponentModel;
2 using Microsoft.Toolkit.Mvvm.Input;
3 using System;
4 using System.Collections;
5 using System.Collections.Generic;
6 using System.Collections.ObjectModel;
7 using System.Linq;
8 using System.Text;
9 using System.Threading.Tasks;
10 using System.Windows;
11 using System.Windows.Controls;
12 using System.Windows.Controls.Primitives;
13 using System.Windows.Input;
14
15 namespace MvvmToolkit学习
16 {
17 public class DataItem
18 {
19 public ObservableCollection<string> Data { get; set; }
20
21 public string Name { get; set; }
22
23 public DataItem()
24 {
25 Data = new ObservableCollection<string>();
26 Data.Add("Sun");
27 Data.Add("Moon");
28 Data.Add("Star");
29 }
30 }
31
32 public class ListBoxHelper
33 {
34 // Using a DependencyProperty as the backing store for SelectedItems. This enables animation, styling, binding, etc...
35 public static readonly DependencyProperty SelectedItemsProperty =
36 DependencyProperty.RegisterAttached("SelectedItems",
37 typeof(IList),
38 typeof(ListBoxHelper),
39 new FrameworkPropertyMetadata(default(IList),
40 FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
41 OnSelectedItemsChanged));
42
43 public static IList GetSelectedItems(DependencyObject obj)
44 {
45 return (IList)obj.GetValue(SelectedItemsProperty);
46 }
47
48 public static void SetSelectedItems(DependencyObject obj, IList value)
49 {
50 obj.SetValue(SelectedItemsProperty, value);
51 }
52
53 private static void OnlistBoxSelectionChanged(object sender, SelectionChangedEventArgs e)
54 {
55 IList dataSource = GetSelectedItems(sender as DependencyObject);
56 //添加用户选中的当前项.
57 foreach (var item in e.AddedItems)
58 {
59 dataSource.Add(item);
60 }
61 //删除用户取消选中的当前项
62 foreach (var item in e.RemovedItems)
63 {
64 dataSource.Remove(item);
65 }
66 }
67
68 private static void OnSelectedItemsChanged(DependencyObject target, DependencyPropertyChangedEventArgs e)
69 {
70 var listBox = target as ListBox;
71 if ((listBox != null) && (listBox.SelectionMode == SelectionMode.Multiple))
72 {
73 if (e.OldValue != null)
74 {
75 listBox.SelectionChanged -= OnlistBoxSelectionChanged;
76 }
77 IList collection = e.NewValue as IList;
78 listBox.SelectedItems.Clear();
79 if (collection != null)
80 {
81 foreach (var item in collection)
82 {
83 listBox.SelectedItems.Add(item);
84 }
85 listBox.SelectionChanged += OnlistBoxSelectionChanged;
86 }
87 }
88 }
89 }
90
91 internal class Test1ViewModel : ObservableObject
92 {
93 private RelayCommand addCmd;
94
95 public ICommand AddCmd
96 {
97 get
98 {
99 if (addCmd == null)
100 {
101 addCmd = new RelayCommand(PerformAddCmd);
102 }
103
104 return addCmd;
105 }
106 }
107
108 public ObservableCollection<DataItem> DataItems { get; set; }
109 public List<DataItem> SelectedItems { get; set; }
110 public double Size { get; set; }
111
112 public Test1ViewModel()
113 {
114 SelectedItems = new List<DataItem>();//此处属性必须赋值，不可为null。。绕了很久的弯路
115 DataItems = new ObservableCollection<DataItem>();
116 DataItems.Add(new DataItem() { Name = "A" });
117 DataItems.Add(new DataItem() { Name = "B" });
118 }
119
120 private void PerformAddCmd()
121 {
122 MessageBox.Show(string.Join("", SelectedItems.Select(s => s.Name)));
123 }
124 }
125 }
xaml
1 <Window
2 x:Class="MvvmToolkit学习.Test1"
3 xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
4 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
5 xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
6 xmlns:local="clr-namespace:MvvmToolkit学习"
7 xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
8 xmlns:pu="clr-namespace:Panuon.UI.Silver;assembly=Panuon.UI.Silver"
9 Title="Test1"
10 Width="800"
11 Height="450"
12 d:DataContext="{d:DesignInstance Type={x:Type local:Test1ViewModel}}"
13 mc:Ignorable="d">
14 <Grid>
15 <StackPanel Orientation="Vertical">
16 <ListBox
17 Width="200"
18 Height="100"
19 local:ListBoxHelper.SelectedItems="{Binding SelectedItems}"
20 ItemsSource="{Binding DataItems}"
21 SelectionMode="Multiple">
22 <ListBox.ItemTemplate>
23 <DataTemplate DataType="{x:Type local:DataItem}">
24 <StackPanel Orientation="Horizontal">
25 <CheckBox IsChecked="{Binding Path=IsSelected, RelativeSource={RelativeSource AncestorType=ListBoxItem, Mode=FindAncestor}}"/>
26 <ContentControl Content="{Binding}"/>
27 </StackPanel>
28 </DataTemplate>
29 </ListBox.ItemTemplate>
30 </ListBox>
31
32 <Button
33 Width="200"
34 Height="35"
35 Command="{Binding AddCmd}"/>
36 <DataGrid pu:DataGridHelper.SelectedItems="{Binding DataItems}"/>
37 </StackPanel>
38 </Grid>
39 </Window>
标签：SelectedItems,System,IList,new,using,WPF,ListBox,public 来源： https://www.cnblogs.com/AtTheMoment/p/16175898.html
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