让ListBox的SelectedItems属性支持数据绑定

　

selecteditems

前天学习了李永伦老师的贴子,关于使用附加属性让ListBox的SeletedItems属性支持数据绑定.今天再把代码复习一下.

原文本在点击打开链接

在Visual Studio里，我们可以通过propa这个代码段快速创建附加属性。值得提醒的是，你必须同时提供GetSelectedItems和SetSelectedItems两个方法，否则无法在XAML里读或写这个附加属性的值。

这里通过自定义的依赖属性SelectedItems来实现数据绑定,注意SelectedItems只能更新IList这个对象,当我们手动向数据源添加Item时,是不会更新到ListBox的 ,因为

IList这个接口并不像ObseverbleCollection那样实现了INotifyCollectionChanged和INotifyPropertyChanged接口.

自定义这个附加属性的过程中,我觉得最让人难理解的就是下面这个判断

if (e.OldValue != null)
                {
                    listBox.SelectionChanged -= OnlistBoxSelectionChanged;
                }

这个判断是用来处理,重复绑定SelectionChanged事件.

要求当数据源发生第二次改变时,取消对SelectionChanged事件的订阅

 public class CustomeSelectionItems
    {
        public static IList GetSelectedItems(DependencyObject obj)
        {
            return (IList)obj.GetValue(SelectedItemsProperty);
        }

        public static void SetSelectedItems(DependencyObject obj, IList value)
        {
            obj.SetValue(SelectedItemsProperty, value);
        }

        //Using a DependencyProperty as the backing store for SelectedItems.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty SelectedItemsProperty =
            DependencyProperty.RegisterAttached("SelectedItems", typeof(IList), typeof(CustomeSelectionItems), new PropertyMetadata(OnSelectedItemsChanged));
        static public void OnSelectedItemsChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var listBox = d as ListBox;
            if ((listBox != null) && (listBox.SelectionMode == SelectionMode.Multiple))
            {
                if (e.OldValue != null)
                {
                    listBox.SelectionChanged -= OnlistBoxSelectionChanged;
                }
                IList collection = e.NewValue as IList;
                listBox.SelectedItems.Clear();
                if (collection != null)
                {
                    foreach (var item in collection)
                    {
                        listBox.SelectedItems.Add(item);
                    }
                    listBox.SelectionChanged += OnlistBoxSelectionChanged;
                }
            }
        }

        static void OnlistBoxSelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            IList dataSource = GetSelectedItems(sender as DependencyObject);
            //添加用户选中的当前项.
            foreach (var item in e.AddedItems)
            {
                dataSource.Add(item);
            }
            //删除用户取消选中的当前项
            foreach (var item in e.RemovedItems)
            {
                dataSource.Remove(item);
            }
        }

xaml

<ListBox Name="lb" SelectionMode="Multiple"
                     ItemsSource="{Binding list}"
                     local:CustomeSelectionItems.SelectedItems="{Binding SelectedItems}"
                     >
                <ListBox.ItemTemplate>
                    <DataTemplate>
                        <StackPanel Orientation="Vertical">
                            <TextBlock Text="{Binding Name}"/>
                            <TextBlock Text="{Binding Sex}"/>
                        </StackPanel>
                    </DataTemplate>
                </ListBox.ItemTemplate>
 </ListBox>

MainPageViewModel

 class MainPageViewModel
    {
        public ObservableCollection<Item> list { get; set; }
        public MainPageViewModel()
        {
            list = new ObservableCollection<Item>();
            list.Add(new Item
            {
                Name = "DDDD",
                Sex = "111",
            });
            list.Add(new Item
            {
                Name = "DDDD",
                Sex = "111",
            });
            list.Add(new Item
            {
                Name = "DDDD",
                Sex = "111",
            });
            list.Add(new Item
            {
                Name = "DDDD",
                Sex = "111",

            });
            list.Add(new Item
            {
                Name = "DDDD",
                Sex = "111",
            });
            SelectedItems = new ObservableCollection<Item>();
            SelectedItems.Add(list[0]);
        }
        public IList<Item> SelectedItems { get; set; }
        
    }

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