从用户控件访问父窗口中的WPF元素

Question

I have a custom menu control in the main window of my WPF application. In main window, I have a frame. I want to change the page in this frame based on the selection in the custom menu control. Below is the code I tried.

    Private Sub NominationMenuItem_Click(sender As Object, e As RoutedEventArgs)
    Dim parentWindow As Window
    parentWindow = Application.Current.MainWindow
    parentWindow.MainFrame.Navigate(New NominationSearch)
End Sub

I know that I can't directly access "MainFrame" control using the "parentWindow" object. How do I rewrite the last line to get a reference to the existing frame object.

Answer 1

It's not appropriate for UserControl to manipulate it's parent. You should let your MainWindow to listen for NominationMenuItem changes via events and then MainWindow itself do the navigation.

So first you need to define an event in your UserControl :

Public Event NominationMenuItemChanged As RoutedEventHandler

Private Sub NominationMenuItem_Click(sender As Object, e As RoutedEventArgs)
    RaiseEvent NominationMenuItemChanged(Me, New RoutedEventArgs())
End Sub

And then listen to this event in your MainWindow :

Public Sub MainWindow()
    AddHandler MyUserControl.NominationMenuItemChanged, AddressOf UC_NominationMenuItemChanged
End Sub

Private Sub UC_NominationMenuItemChanged(sender As Object, e As RoutedEventArgs)
    MainFrame.Navigate(MyUserControl.NominationSearch)
End Sub