在运行时添加到 ListBox 的项目永远不会获得焦点

Question

如上图所示，我在列表框中有三列。

第一列是名字，第二列是姓氏，第三列是年龄。

当我在年龄列上按 Enter 时，一个新的人被添加到列表中。这最终反映了 ListBox 的变化。

问题：

当我在年龄列上按 Enter 时，我按预期添加了一个新人。但焦点不会转到下一个 ListItem。无论我按 Enter 多少次，我都不会关注以编程方式添加的项目。

示例：

我创建了一个重现该问题的示例项目：

Download Sample Project

我有一个 ListBox 如下：

<ListBox ItemsSource="{Binding People}" SelectedItem="{Binding SelectedPerson}">

    <ListBox.Resources>
        <Style TargetType="ListBoxItem" BasedOn="{StaticResource {x:Type ListBoxItem}}">
            <Style.Triggers>
                <Trigger Property="IsKeyboardFocusWithin" Value="True">
                    <Setter Property="IsSelected" Value="True"></Setter>
                </Trigger>
            </Style.Triggers>
            <Setter Property="Focusable" Value="False" />
        </Style>
    </ListBox.Resources>

    <ListBox.ItemTemplate>

        <DataTemplate>

            <Grid x:Name="CurrentItemGrid">

                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="200" />
                    <ColumnDefinition Width="200" />
                    <ColumnDefinition Width="100" />
                </Grid.ColumnDefinitions>

                <TextBox Text="{Binding FirstName, UpdateSourceTrigger=PropertyChanged}" Tag="IgnoreEnterKeyTraversal">

                    <TextBox.InputBindings>
                        <KeyBinding Command="{Binding DataContext.DeleteUnwantedOrderItemTransactionCommand, 
                                                              RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Window}}}"
                                            Gesture="Return" />
                        <KeyBinding Command="{Binding DataContext.DeleteUnwantedOrderItemTransactionCommand, 
                                                              RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Window}}}"
                                            Gesture="Tab" />
                    </TextBox.InputBindings>

                </TextBox>

                <TextBox Grid.Column="1" Text="{Binding LastName, UpdateSourceTrigger=PropertyChanged}" Margin="5,0"/>

                <TextBox Grid.Column="2" Text="{Binding Age, UpdateSourceTrigger=PropertyChanged}" Margin="5,0" Tag="IgnoreEnterKeyTraversal">

                    <TextBox.InputBindings>
                        <KeyBinding Command="{Binding DataContext.AddNewOrderItemTransactionCommand, 
                                                              RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Window}}}"
                                            Gesture="Return" />
                        <KeyBinding Command="{Binding DataContext.AddNewOrderItemTransactionCommand, 
                                                              RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Window}}}"
                                            Gesture="Tab" />
                    </TextBox.InputBindings>
                </TextBox>

            </Grid>

        </DataTemplate>

    </ListBox.ItemTemplate>

</ListBox>

在 ViewModel 中：

public class MainWindowViewModel : INotifyPropertyChanged
{
    IEventAggregator eventAggregator;

    public MainWindowViewModel(IEventAggregator _eventAggregator)
    {
        People = new ObservableCollection<Person>();
        People.Add(new Person());
        eventAggregator = _eventAggregator;

        DeleteUnwantedOrderItemTransactionCommand = new RelayCommand(DeleteUnwantedOrderItemTransaction);
        AddNewOrderItemTransactionCommand = new RelayCommand(AddNewOrderItemTransaction);
    }

    public RelayCommand DeleteUnwantedOrderItemTransactionCommand { get; set; }
    public RelayCommand AddNewOrderItemTransactionCommand { get; set; }

    private ObservableCollection<Person> _People;

    public ObservableCollection<Person> People
    {
        get
        {
            return _People;
        }
        set
        {
            if (_People != value)
            {
                _People = value;
                OnPropertyChanged("People");
            }
        }
    }

    private Person _SelectedPerson;

    public Person SelectedPerson
    {
        get
        {
            return _SelectedPerson;
        }
        set
        {
            if (_SelectedPerson != value)
            {
                _SelectedPerson = value;
                OnPropertyChanged("SelectedPerson");
            }
        }
    }

    protected void DeleteUnwantedOrderItemTransaction(object obj)
    {
        if (SelectedPerson.FirstName == "")
        {
            People.Remove(SelectedPerson);
        }

        if (People.Count == 0)
        {
            People.Add(new Person());
        }

        eventAggregator.GetEvent<ChangeFocusToNextUIElementEvent>().Publish(true);
    }

    protected void AddNewOrderItemTransaction(object obj)
    {
        if (SelectedPerson == People.Last())
            People.Add(new Person());

        eventAggregator.GetEvent<ChangeFocusToNextUIElementEvent>().Publish(true);
    }

    public event PropertyChangedEventHandler PropertyChanged;

    private void OnPropertyChanged(String info)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(info));
        }
    }
}

在代码隐藏中：

public partial class MainWindow : Window
{
    IEventAggregator _eventAggregator = new EventAggregator();

    public MainWindow()
    {
        InitializeComponent();
        this.DataContext = new MainWindowViewModel(_eventAggregator);
        _eventAggregator.GetEvent<ChangeFocusToNextUIElementEvent>().Subscribe(MoveToNextUIElement);
    }

    void MoveToNextUIElement(bool obj)
    {
        // Gets the element with keyboard focus.
        UIElement elementWithFocus = Keyboard.FocusedElement as UIElement;

        if (elementWithFocus != null)
        {
            elementWithFocus.MoveFocus(new TraversalRequest(FocusNavigationDirection.Next));
        }
    }
}

Answer 1

在您触发事件的那一刻，您已将元素添加到 VM，但它可能尚未由视图 (ListBox) 绑定和创建。以低优先级调度焦点请求可能会有所帮助。还要检查是否可以通过按 TAB 访问元素，以便知道遍历是否有效。

elementWithFocus.Dispatcher.Invoke(() => 
    elementWithFocus.MoveFocus(new TraversalRequest(FocusNavigationDirection.Next)),
    DispatcherPriority.Input); // !

ListBox 元素的虚拟化也可能是一个问题。您必须将添加的项目显示在视图中。

干杯。