WPF ListView：MVVM模式下选中项变更时自动聚焦问题求助

我来帮你搞定这个问题，完全符合MVVM模式，不用让ViewModel引用任何视图类，下面给你两种实用的方案：

方法一：用附加属性（轻量高效，最推荐） #

附加属性可以把视图层的滚动、聚焦逻辑封装起来，ViewModel只需要管好数据就行。

首先写一个静态的附加属性类：

using System.Windows;
using System.Windows.Controls;

public static class ListViewAutoScrollHelper
{
    // 定义附加属性：开启自动滚动到选中项
    public static readonly DependencyProperty AutoScrollToSelectedProperty =
        DependencyProperty.RegisterAttached(
            "AutoScrollToSelected",
            typeof(bool),
            typeof(ListViewAutoScrollHelper),
            new PropertyMetadata(false, OnAutoScrollChanged));

    public static bool GetAutoScrollToSelected(DependencyObject obj)
    {
        return (bool)obj.GetValue(AutoScrollToSelectedProperty);
    }

    public static void SetAutoScrollToSelected(DependencyObject obj, bool value)
    {
        obj.SetValue(AutoScrollToSelectedProperty, value);
    }

    private static void OnAutoScrollChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if (d is ListView listView)
        {
            if ((bool)e.NewValue)
            {
                // 监听选中项变化事件
                listView.SelectionChanged += ListView_SelectionChanged;
            }
            else
            {
                listView.SelectionChanged -= ListView_SelectionChanged;
            }
        }
    }

    private static void ListView_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        var listView = sender as ListView;
        if (listView?.SelectedItem == null) return;

        // 滚动到选中项，确保它在视图里
        listView.ScrollIntoView(listView.SelectedItem);

        // 如果需要让该项获得键盘焦点，加上下面这行
        var selectedItemContainer = listView.ItemContainerGenerator.ContainerFromItem(listView.SelectedItem) as ListViewItem;
        selectedItemContainer?.Focus();
    }
}

然后在XAML里给ListView加上这个属性：

<ListView ItemsSource="{Binding YourItemCollection}"
          SelectedItem="{Binding CurrentSelectedItem}"
          local:ListViewAutoScrollHelper.AutoScrollToSelected="True">
    <!-- 这里放你的ItemTemplate -->
</ListView>

接下来ViewModel里只需要维护CurrentSelectedItem（或者模型的IsSelected属性）就行：

public class YourViewModel : INotifyPropertyChanged
{
    private ObservableCollection<YourModel> _yourItemCollection;
    private YourModel _currentSelectedItem;

    public ObservableCollection<YourModel> YourItemCollection
    {
        get => _yourItemCollection;
        set { _yourItemCollection = value; OnPropertyChanged(); }
    }

    public YourModel CurrentSelectedItem
    {
        get => _currentSelectedItem;
        set { _currentSelectedItem = value; OnPropertyChanged(); }
    }

    // 当PC/SC读卡器触发时，调用这个方法切换选中项
    public void SwitchToNextItem()
    {
        var currentIndex = YourItemCollection.IndexOf(CurrentSelectedItem);
        var nextIndex = (currentIndex + 1) % YourItemCollection.Count;
        CurrentSelectedItem = YourItemCollection[nextIndex];
    }

    public event PropertyChangedEventHandler PropertyChanged;
    protected void OnPropertyChanged([CallerMemberName] string propName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propName));
    }
}

如果你的模型用的是IsSelected属性，记得给ListView的ItemContainerStyle绑定这个属性：

<ListView ItemsSource="{Binding YourItemCollection}">
    <ListView.ItemContainerStyle>
        <Style TargetType="ListViewItem">
            <Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay}" />
        </Style>
    </ListView.ItemContainerStyle>
    <local:ListViewAutoScrollHelper.AutoScrollToSelected>True</local:ListViewAutoScrollHelper.AutoScrollToSelected>
</ListView>

这样当你修改模型的IsSelected为true时，ListView会自动选中该项，然后附加属性会帮你完成滚动和聚焦。

方法二：用Blend行为（更灵活，适合复杂场景） #

如果你的项目已经在用Microsoft的XAML行为库，用行为来实现也很方便。

首先安装NuGet包：Microsoft.Xaml.Behaviors.Wpf

然后写一个行为类：

using Microsoft.Xaml.Behaviors;
using System.Windows.Controls;

public class AutoScrollToSelectedBehavior : Behavior<ListView>
{
    protected override void OnAttached()
    {
        base.OnAttached();
        AssociatedObject.SelectionChanged += OnSelectionChanged;
    }

    protected override void OnDetaching()
    {
        AssociatedObject.SelectionChanged -= OnSelectionChanged;
        base.OnDetaching();
    }

    private void OnSelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        if (AssociatedObject.SelectedItem == null) return;

        AssociatedObject.ScrollIntoView(AssociatedObject.SelectedItem);
        var itemContainer = AssociatedObject.ItemContainerGenerator.ContainerFromItem(AssociatedObject.SelectedItem) as ListViewItem;
        itemContainer?.Focus();
    }
}

在XAML里使用这个行为，记得先加命名空间：

xmlns:i="http://schemas.microsoft.com/xaml/behaviors"

<ListView ItemsSource="{Binding YourItemCollection}"
          SelectedItem="{Binding CurrentSelectedItem}">
    <i:Interaction.Behaviors>
        <local:AutoScrollToSelectedBehavior />
    </i:Interaction.Behaviors>
    <!-- ItemTemplate -->
</ListView>

核心思路 #

这两种方案都严格遵循MVVM：ViewModel只处理数据逻辑，视图层的滚动、聚焦逻辑都封装在附加属性或行为里，ViewModel完全不需要引用任何View相关的类型，完美解决你的需求~

内容的提问来源于stack exchange，提问作者Guillaume Raymond