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c# - 来自视图模型的 WPF 列表框焦点

问题描述

我偶然发现了 Listbox 和 focus 的众所周知的问题。我ItemsSource从 viewmodel 设置，在某些时候我需要重新加载它们并将选择和焦点设置到特定项目，比如：

private readonly ObservableCollection<ItemViewModel> items;
private ItemViewModel selectedItem;

private void Process()
{
    items.Clear();

    for (int i = 0; i < 100; i++)
    {
        items.Add(new ItemViewModel(i));
    }

    var item = items.FirstOrDefault(i => i.Value == 25);
    SelectedItem = item;
}

public ObservableCollection<ItemViewModel> Items { /* usual stuff */ }
public ItemViewModel SelectedItem { /* usual stuff */ }

绑定可能如下所示：

<ListBox ItemsSource="{Binding Items}" SelectedItem="{Binding SelectedItem}" />

调用方法后，项目被选中，但没有获得焦点。

我在 Internet 和 StackOverflow 上阅读了很多内容，但我找到的所有答案都涉及手动填充列表框，而不是通过来自 viewmodel 的绑定。所以问题是：如何在呈现的场景中正确关注新选择的项目？

为了添加一些上下文，我正在实现一个侧边栏文件浏览器：

探险家

我需要在树视图下方的列表框中进行键盘导航。

标签： c#wpflistboxfocus

解决方案

这是一个可能对您有用的解决方案：

控制：

class FocusableListBox : ListBox
{
    #region Dependency Proeprty

    public static readonly DependencyProperty IsFocusedControlProperty = DependencyProperty.Register("IsFocusedControl", typeof(Boolean), typeof(FocusableListBox), new UIPropertyMetadata(false, OnIsFocusedChanged));

    public Boolean IsFocusedControl
    {
        get { return (Boolean)GetValue(IsFocusedControlProperty); }
        set { SetValue(IsFocusedControlProperty, value); }
    }

    public static void OnIsFocusedChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
    {
        ListBox listBox = dependencyObject as ListBox;
        listBox.Focus();
    }

    #endregion Dependency Proeprty
}

视图模型：

 class ViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    private Boolean _IsFocused;
    private String selectedItem;

    public ObservableCollection<String> Items { get; private set; }
    public String SelectedItem
    {
        get
        {
            return selectedItem;
        }
        set
        {
            selectedItem = value;
            RaisePropertyChanged("SelectedItem");
        }
    }      

    public Boolean IsFocused
    {
        get { return _IsFocused; }
        set
        {
            _IsFocused = value;
            RaisePropertyChanged("IsFocused");
        }
    }

    public ViewModel()
    {
        Items = new ObservableCollection<string>();
        Process();
    }

    private void Process()
    {
        Items.Clear();

        for (int i = 0; i < 100; i++)
        {
            Items.Add(i.ToString());
        }

        ChangeFocusedElement("2");
    }

    public void ChangeFocusedElement(string newElement)
    {
        var item = Items.FirstOrDefault(i => i == newElement);
        IsFocused = false;
        SelectedItem = item;
        IsFocused = true;
    }

    private void RaisePropertyChanged(String propName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propName));
    }
}

XAML：

<local:FocusableListBox ItemsSource="{Binding Items}" SelectedItem="{Binding SelectedItem}" 
                            HorizontalAlignment="Left" VerticalAlignment="Stretch"
                            ScrollViewer.VerticalScrollBarVisibility="Auto"
                            Width="200" 
                            IsFocusedControl="{Binding IsFocused, Mode=TwoWay}"/>

更新调用：

 _viewModel.ChangeFocusedElement("10");

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