xamarin - 导航页面 + 轮播页面 : weird scroll error

Question

我现在正在使用 CarouselPage 示例，并且由于我想移动到其他页面，因此我以 NavigationPage 作为主要页面来启动应用程序一:

    public App()
    {
        InitializeComponent();

        // Need navigation to have modal/nonmodal pages
        //MainPage = new MainPage();
        MainPage = new NavigationPage(new MainPage());
    }

XAML 为 iPhone X 添加安全区域，并删除导航栏:

<?xml version="1.0" encoding="utf-8"?>
<CarouselPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" xmlns:local="clr-namespace:Stoa" x:Class="Test.MainPage"
              xmlns:ios="clr-namespace:Xamarin.Forms.PlatformConfiguration.iOSSpecific;assembly=Xamarin.Forms.Core" 
              ios:Page.UseSafeArea="true" 
              NavigationPage.HasNavigationBar="False">            
    <ContentPage>
        <ContentPage.Padding>
            <OnPlatform x:TypeArguments="Thickness">
                <On Platform="iOS, Android" Value="0,40,0,0" />
            </OnPlatform>
        </ContentPage.Padding>
        <StackLayout>
            <Label Text="Green" FontSize="Medium" HorizontalOptions="Center" />
            <Button BackgroundColor="Green" WidthRequest="200" HeightRequest="200" HorizontalOptions="Center" VerticalOptions="CenterAndExpand" />
        </StackLayout>
    </ContentPage>
    <ContentPage>
        <ContentPage.Padding>
            <OnPlatform x:TypeArguments="Thickness">
                <On Platform="iOS, Android" Value="0,40,0,0" />
            </OnPlatform>
        </ContentPage.Padding>
        <StackLayout>
            <Label Text="Blue" FontSize="Medium" HorizontalOptions="Center" />
            <Button BackgroundColor="Blue" WidthRequest="200" HeightRequest="200" HorizontalOptions="Center" VerticalOptions="CenterAndExpand" />
        </StackLayout>
    </ContentPage>
</CarouselPage>

问题是，现在用户可以垂直滚动，并且显然会失去边距:

有办法解决这个问题吗？

或者，如何离开轮播 View 或“伪造”轮播？

Answer 1

This "Safe Area scroll offset" can be fixed with a custom iOS CarouselPageRenderer that sets the UIScrollView ContentInsetAdjustmentBehavior to Never

Updated: previous code example checked UIView.Subviews[0] is UIScrollView in OnElementChanged, this could throw a System.IndexOutOfRangeException causing a SIGABRT crash. So instead we check it in ViewDidLoad as suggested here: https://forums.xamarin.com/discussion/104385/ios-11-carousel-page-issues

[assembly: ExportRenderer(typeof(CarouselPage), typeof(CustomCarouselPageRenderer))]
namespace MyApp.iOS.Renderers
{
    public class CustomCarouselPageRenderer : CarouselPageRenderer
    {
        public override void ViewDidLoad()
        {
            base.ViewDidLoad();

            //Prevent vertical carousel scroll on iOS 11, 
            //we only want horizontal scroll in the carousel
            if (UIDevice.CurrentDevice.CheckSystemVersion(11, 0))
            {
             View.Subviews.OfType<UIScrollView>().Single().ContentInsetAdjustmentBehavior =
             UIScrollViewContentInsetAdjustmentBehavior.Never;
            }
        } 
    }
}