如何使用交互行为在不同控件之间移动焦点？

Question

我有一个WPF应用程序，其中我有一个TextBox和一个ListBox。受this SO thread的启发，我已经实现了一种行为，我可以通过按下向下键将焦点从TextBox移动到ListBox。然而，问题是它只发生一次，即OnIsFocusedChanged只触发一次。谁能告诉我我错过了什么或做错了什么？

视图：

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                xmlns:local="clr-namespace:InteractivityTest"
                xmlns:beh="clr-namespace:InteractivityTest.Behaviors"
                xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity">
    <DataTemplate DataType="{x:Type local:AutoCopmleteTextBoxViewModel}">
        <Grid Name="grMain">
            <TextBox Name="myTextBox"
                     Text="{Binding MyText}"
                     Width="150">
                <i:Interaction.Behaviors>
                    <beh:FocusBehavior IsFocused="{Binding TextBoxHasFocus}" />
                </i:Interaction.Behaviors>

                <TextBox.InputBindings>
                    <KeyBinding Key="Down"
                                Command="{Binding SetFocusToListBoxCommand}" />
                </TextBox.InputBindings>
            </TextBox>

            <Popup Name="puSuggestions"
                   Placement="Bottom"
                   Width="{Binding ElementName=myTextBox, Path=ActualWidth}"
                   MinWidth="0"
                   PlacementTarget="{Binding ElementName=myTextBox}"
                   IsOpen="True">
                <Border Background="White"
                        BorderBrush="Gray"
                        BorderThickness="1"
                        CornerRadius="1">
                    <ListBox Name="lbSuggestions"
                             ItemsSource="{Binding SuggestionCol}"
                             BorderThickness="0"
                             Background="White">
                        <i:Interaction.Behaviors>
                            <beh:FocusBehavior IsFocused="{Binding ListBoxHasFocus}" />
                        </i:Interaction.Behaviors>
                    </ListBox>
                </Border>
            </Popup>
        </Grid>
    </DataTemplate>
</ResourceDictionary>

视图模型：

Imports System.ComponentModel

Public Class AutoCopmleteTextBoxViewModel
    Implements INotifyPropertyChanged

    Private _SuggestionCol As List(Of String)
    Private _ListBoxHasFocus As Boolean
    Private _TextBoxHasFocus As Boolean

    Public Property SuggestionCol As List(Of String)
        Get
            Return New List(Of String) From {"A", "AB", "ABC", "ABCD"}
        End Get
        Set
            _SuggestionCol = Value
            NotifyPropertyChanged(NameOf(SuggestionCol))
        End Set
    End Property

    Public Property ListBoxHasFocus As Boolean
        Get
            Return _ListBoxHasFocus
        End Get
        Set
            _ListBoxHasFocus = Value
            NotifyPropertyChanged(NameOf(ListBoxHasFocus))
        End Set
    End Property

    Public Property TextBoxHasFocus As Boolean
        Get
            Return _TextBoxHasFocus
        End Get
        Set
            _TextBoxHasFocus = Value
            NotifyPropertyChanged(NameOf(TextBoxHasFocus))
        End Set
    End Property

    Public Property SetFocusToListBoxCommand As ICommand

    Sub New()
        SetFocusToListBoxCommand = New Command(AddressOf Me.OnKeyDownOnTextBox, Nothing)
    End Sub

    Private Sub OnKeyDownOnTextBox(parameter As Object)
        ListBoxHasFocus = True
        TextBoxHasFocus = False
    End Sub

#Region "Property Changed"
    Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged

    Protected Sub NotifyPropertyChanged(info As [String])
        RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(info))
    End Sub
#End Region
End Class

行为：

Imports System.Windows.Interactivity

Namespace Behaviors
    Public Class FocusBehavior
        Inherits Behavior(Of Control)

        Public Property IsFocused As Boolean
            Get
                Return CBool(GetValue(IsFocusedProperty))
            End Get
            Set(ByVal value As Boolean)
                SetValue(IsFocusedProperty, value)
            End Set
        End Property
        Public Shared ReadOnly IsFocusedProperty As DependencyProperty =
            DependencyProperty.Register(NameOf(IsFocused), GetType(Boolean),
                                        GetType(FocusBehavior),
                                        New PropertyMetadata(New PropertyChangedCallback(Sub(d, e)
                                                                                             OnIsFocusedChanged(d, e)
                                                                                         End Sub)))

        Private Shared Sub OnIsFocusedChanged(ByVal d As DependencyObject, ByVal e As DependencyPropertyChangedEventArgs)
            If CBool(e.NewValue) Then
                CType(d, FocusBehavior).GotFocus()
            End If
        End Sub

        Private Sub GotFocus()
            Me.AssociatedObject.Focus()
            Keyboard.Focus(Me.AssociatedObject)
            If TypeOf Me.AssociatedObject Is TextBox Then
                Dim tmpTextBox = TryCast(Me.AssociatedObject, TextBox)
                tmpTextBox.CaretIndex = tmpTextBox.Text.Length
            ElseIf TypeOf Me.AssociatedObject Is ListBox Then
                Dim tmpListBox = TryCast(Me.AssociatedObject, ListBox)
                If Not tmpListBox.Items.Count = 0 Then
                    tmpListBox.SelectedItem = tmpListBox.Items(0)
                    Dim tmpListBoxItem = TryCast(tmpListBox.ItemContainerGenerator.ContainerFromItem(tmpListBox.SelectedItem), ListBoxItem)
                    tmpListBoxItem.Focus()
                End If
            End If
        End Sub
    End Class
End Namespace

Answer 1

当依赖属性的值设置为新值并且在OnIsFocusedChanged方法中似乎只设置为新值时，您正在调用OnKeyDownOnTextBox。

您需要更改ListBoxHasFocus和TextBoxHasFocus源属性的值，以便在TextBox或ListBox实际获得焦点时重置它们。