WPF MVVM - 重复设置焦点和丢失焦点事件

Question

我是MVVM模式的新手，在我的应用程序中，当文本框的验证在该文本框失去焦点时出错时，焦点必须保持在同一文本本身，当我尝试实现时，设置焦点的方法和失去焦点的是反复呼唤。

设置焦点方法

Public Sub MainMenu_Focus(sender As Object, e As MainWindowEventArgs)
                      If TxtEditNDCClinicalScreen.IsEnabled Then
                ' TxtEditNDCClinicalScreen.Focus()
                Keyboard.Focus(TxtEditNDCClinicalScreen)
                If TxtEditNDCClinicalScreen.GetType() Is GetType(TextEdit) Then
                    CType(TxtEditNDCClinicalScreen, TextEdit).SelectAll()
                End If
            End If
        End Sub

失去焦点的方法

Private Sub TxtEditNDCClinicalScreen_LostFocus(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles TxtEditNDCClinicalScreen.LostFocus
            VM.CommandFind(TxtEditNDCClinicalScreen.Text.Length)
        End Sub

我也尝试过互动触发器，但没有用..面临同样的问题。

  <i:Interaction.Triggers> 
                        <i:EventTrigger EventName="LostFocus"> 
                            <i:InvokeCommandAction Command="{Binding CommandLostFocus}" CommandParameter="{Binding Path=Text.Length,ElementName=TxtEditNDCClinicalScreen}"  />
                        </i:EventTrigger> IsHitTestVisible="True"
                    </i:Interaction.Triggers>

请建议如何解决问题 感谢名单。