Java.Lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.

[Kim99]

Java.Lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.

[Kim99]

    public MainPage()
    {
        InitializeComponent();
        NavigationPage.SetHasNavigationBar(this, false);
       
        this.Appearing += (s, e) =>
        {
            this.Navigation.PushAsync(new NavigationPage(new TabbedPage1()));
        };
    }

[Kim99]

why？why？why？