Controls not showing in masterdetail Page

I have an issue, my controls(button, entry) not showing when I am using navigation page but toolbar and menu showing. Without the navigation page, the controls appear but the menu disappears.
In App.cs

public App() => MainPage = new RootPage();

In RootPage.cs

class RootPage : MasterDetailPage
{
.....
Detail =new NavigationPage(new MathInputPage());
....
void OnItemSelectedAsync(object sender, SelectedItemChangedEventArgs e)
{
    .....
     Detail.Navigation.PushAsync((Page)Activator.CreateInstance(item.TargetType));
    ......
}
}

Above code, the menu, as well as the back button, is shown. But controls not showing.

Then I altered this code into
In RootPage.cs

class RootPage : MasterDetailPage
{
.....
Detail =new MathInputPage();
....
void OnItemSelectedAsync(object sender, SelectedItemChangedEventArgs e)
{
    .....
     Detail=(Page)Activator.CreateInstance(item.TargetType);
    ......
}
}