Silverlight 在MVVM中同步UI的SelectedItems和DataContext

以RadGradView为例，先写DataContext:

    public class MyDataContext : INotifyPropertyChanged
    {
        ...
        ObservableCollection<MyObject> _SelectedItems;
        public ObservableCollection<MyObject> SelectedItems
        {
            get
            {
                if (_SelectedItems == null)
                {
                    _SelectedItems = new ObservableCollection<MyObject>();
                }
                return _SelectedItems;
            }
        }

        MyObject _SelectedItem;
        public MyObject SelectedItem
        {
            get
            {
                return _SelectedItem;
            }
            set
            {
                if (_SelectedItem != value)
                {
                    _SelectedItem = value;

                    OnPropertyChanged("SelectedItem");
                }
            }
        }
    ...    }

RadGridView的SelectedItems属于只读的，所以不能通过TwoWay Binding这个属性，那我们该怎么做呢？这里我们使用behaviors。

使用System.Windows.Interactivity.Behavior<T>，如下：

    public class MyMultiSelectBehavior : Behavior<RadGridView>
    {
        private RadGridView Grid
        {
            get
            {
                return Associatedobject as RadGridView;
            }
        }

        public INotifyCollectionChanged SelectedItems
        {
            get { return (INotifyCollectionChanged)GetValue(SelectedItemsProperty); }
            set { SetValue(SelectedItemsProperty,value); }
        }

        public static readonly DependencyProperty SelectedItemsProperty =
            DependencyProperty.Register("SelectedItems",typeof(INotifyCollectionChanged),typeof(MyMultiSelectBehavior),new PropertyMetadata(OnSelectedItemsPropertyChanged));


        private static void OnSelectedItemsPropertyChanged(DependencyObject target,DependencyPropertyChangedEventArgs args)
        {
            var collection = args.NewValue as INotifyCollectionChanged;
            if (collection != null)
            {
                collection.CollectionChanged += ((MyMultiSelectBehavior)target).ContextSelectedItems_CollectionChanged;
            }
        }

        protected override void OnAttached()
        {
            base.OnAttached();

            Grid.SelectedItems.CollectionChanged += GridSelectedItems_CollectionChanged;
        }
        ...     }

下面就是在页面上如何绑定：

<UserControl x:Class="SilverlightApplication1.MainPage"
    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:telerik="http://schemas.telerik.com/2008/xaml/presentation"
    xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
    xmlns:local="clr-namespace:SilverlightApplication1" mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400">
    <UserControl.Resources>
        <local:MyDataContext x:Key="context"/>
    </UserControl.Resources>
    <Grid x:Name="LayoutRoot" Background="White" DataContext="{StaticResource context}">
        <Grid.ColumnDeFinitions>
            <ColumnDeFinition />
            <ColumnDeFinition Width="200" />
        </Grid.ColumnDeFinitions>
        <telerik:RadGridView ItemsSource="{Binding Data}" SelectionMode="Extended" SelectedItem="{Binding SelectedItem,Mode=TwoWay}">
          <i:Interaction.Behaviors> <local:MyMultiSelectBehavior SelectedItems="{Binding SelectedItems,Source={StaticResource context}}" /> </i:Interaction.Behaviors>
        </telerik:RadGridView>
        <StackPanel Orientation="Vertical" Grid.Column="1">
            <telerik:RadButton Content="Clear selected items" Click="Button_Click" />
            <TextBlock Text="Selected items:"/>
            <ListBox ItemsSource="{Binding SelectedItems}" displayMemberPath="ID" />
        </StackPanel>
    </Grid>
</UserControl>

文章转载于:http://blogs.telerik.com/blogs/posts/10-05-31/how-to-synchronize-your-ui-selected-items-with-your-data-context-using-mvvm-and-blend-behaviors-for-silverlight-and-wpf.aspx

源代码下载：
 http://download.csdn.net/detail/tianyu0910/4093881