silverlight-3.0 – 使用ViewModel中的集合在Muliselect列表框中同步SelectedItem

public ObservableCollection<String> AllItems { get; private set; }
public ObservableCollection<String> SELEctedItems { get; private set; }

您将首先将AllItems集合绑定到ListBox：

<ListBox x:Name="MyListBox" Itemssource="{Binding AllItems}" SELEctionMode="Multiple" />

问题是ListBox上的SELEctedItems属性不是DependencyProperty。这是非常糟糕的，因为您无法将其绑定到viewmodel中的某个东西。

第一种方法是将这个逻辑放在代码隐藏中，调整viewmodel：

public MainPage()
{
    InitializeComponent();

    MyListBox.SELEctionChanged += ListBoxSELEctionChanged;
}

private static void ListBoxSELEctionChanged(object sender,SELEctionChangedEventArgs E)
{
    var listBox = sender as ListBox;
    if(listBox == null) return;

    var viewmodel = listBox.DataContext as MainVM;
    if(viewmodel == null) return;

    viewmodel.SELEctedItems.Clear();

    foreach (String item in listBox.SELEctedItems)
    {
        viewmodel.SELEctedItems.Add(item);
    }
}

这种做法会奏效，但真的很丑陋。我的首选方法是将此行为提取为“附加行为”。如果您这样做，您可以完全消除您的代码隐藏并将其设置在XAML中。奖金是这个“附加行为”现在可以在任何ListBox中重用：

<ListBox Itemssource="{Binding AllItems}" Demo:SELEctedItems.Items="{Binding SELEctedItems}" SELEctionMode="Multiple" />

这里是附加行为的代码：

public static class SELEctedItems
{
    private static readonly DependencyProperty SELEctedItemsBehaviorProperty =
        DependencyProperty.RegisterAttached(
            "SELEctedItemsBehavior",typeof(SELEctedItemsBehavior),typeof(ListBox),null);

    public static readonly DependencyProperty ItemsProperty = DependencyProperty.RegisterAttached(
            "Items",typeof(IList),typeof(SELEctedItems),new PropertyMetadata(null,ItemsPropertyChanged));

    public static void SetItems(ListBox listBox,IList list) { listBox.@R_801_6938@ue(ItemsProperty,list); }
    public static IList GetItems(ListBox listBox) { return listBox.GetValue(ItemsProperty) as IList; }

    private static void ItemsPropertyChanged(DependencyObject d,DependencyPropertyChangedEventArgs E)
    {
        var target = d as ListBox;
        if (target != null)
        {
            GetOrCreateBehavior(target,e.NewValue as IList);
        }
    }

    private static SELEctedItemsBehavior getOrCreateBehavior(ListBox target,IList list)
    {
        var behavior = target.GetValue(SELEctedItemsBehaviorProperty) as SELEctedItemsBehavior;
        if (behavior == null)
        {
            behavior = new SELEctedItemsBehavior(target,list);
            target.@R_801_6938@ue(SELEctedItemsBehaviorProperty,behavior);
        }

        return behavior;
    }
}

public class SELEctedItemsBehavior
{
    private readonly ListBox _listBox;
    private readonly IList _boundList;

    public SELEctedItemsBehavior(ListBox listBox,IList boundList)
    {
        _boundList = boundList;
        _listBox = listBox;
        _listBox.SELEctionChanged += OnSELEctionChanged;
    }

    private void OnSELEctionChanged(object sender,SELEctionChangedEventArgs E)
    {
        _boundList.Clear();

        foreach (var item in _listBox.SELEctedItems)
        {
            _boundList.Add(item);
        }
    }
}