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，其中有一个 TextBox 和一个 ListBox。受 this SO thread 的启发，我实现了一个行为，通过按下向下键，我可以将焦点从 TextBox 移动到 ListBox。但是，问题是它只发生一次，即 OnIsFocusedChanged 只触发一次。谁能告诉我我遗漏了什么或做错了什么？

查看：

<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>

ViewModel:

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

当依赖项 属性 的值设置为 new 值时，您正在调用 OnIsFocusedChanged 并且它似乎只设置为新的在您的 OnKeyDownOnTextBox 方法中值一次。

您需要更改 ListBoxHasFocus 和 TextBoxHasFocus 源属性的值，以便在 TextBox 或 ListBox 实际接收到焦点时重置它们。