TreeView在View模型中同步到SelectedItem

Question

我在WPF TreeView控件之上有一个ViewModel.我希望ViewModel能够从TreeView中设置和读取SelectedItem.但是,TreeView的SelectedItem属性不可绑定.

我能够在后面的代码中设置和获取所选项(使用ItemContainerGenerator和TreeViewItem.IsSelected = true)但这会导致后面的代码和ViewModel之间的一些丑陋的通信.

有人有一个干净的解决方案吗？

Answer 1

您可以使用某种代理类将 SelectedItem 属性绑定到 In 属性，并将 Out 属性绑定到您的 ViewModel：

    public class Proxy : FrameworkElement
    {
    public static readonly DependencyProperty InProperty;
    public static readonly DependencyProperty OutProperty;

    public Proxy()
    {
        Visibility = Visibility.Collapsed;
    }

    static Proxy()
    {
        var inMetadata = new FrameworkPropertyMetadata(
            delegate(DependencyObject p, DependencyPropertyChangedEventArgs args)
                {
                    if (null != BindingOperations.GetBinding(p, OutProperty))
                    {
                        var proxy = p as Proxy;
                        if (proxy != null)
                            proxy.Out = args.NewValue;
                    }
                });

        inMetadata.BindsTwoWayByDefault = false;
        inMetadata.DefaultUpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;

        InProperty = DependencyProperty.Register("In",
                                                 typeof (object),
                                                 typeof (Proxy),
                                                 inMetadata);

        var outMetadata = new FrameworkPropertyMetadata(
            delegate(DependencyObject p, DependencyPropertyChangedEventArgs args)
                {
                    ValueSource source = DependencyPropertyHelper.GetValueSource(p, args.Property);

                    if (source.BaseValueSource != BaseValueSource.Local)
                    {
                        var proxy = p as Proxy;
                        if (proxy != null)
                        {
                            var expected = proxy.In;
                            if (!ReferenceEquals(args.NewValue, expected))
                            {
                                Dispatcher.CurrentDispatcher.BeginInvoke(
                                    DispatcherPriority.DataBind, new Action(delegate
                                                                                {
                                                                                    proxy.Out = proxy.In;
                                                                                }));
                            }
                        }
                    }
                });

        outMetadata.BindsTwoWayByDefault = true;
        outMetadata.DefaultUpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;

        OutProperty = DependencyProperty.Register("Out",
                                                  typeof (object),
                                                  typeof (Proxy),
                                                  outMetadata);
    }

    public object In
    {
        get { return GetValue(InProperty); }
        set { SetValue(InProperty, value); }
    }

    public object Out
    {
        get { return GetValue(OutProperty); }
        set { SetValue(OutProperty, value); }
    }
}
<Proxy In="{Binding ElementName=Tree, Path=SelectedItem}" Out="{Binding SelectedItem, UpdateSourceTrigger=PropertyChanged}"/>
<TreeView x:Name="Tree" ItemsSource="{Binding Path=Items}"/>