Background image with Carousel effect - xamarin

Question

I would like to create a layout with a fullscreen background image and some UI elements on top of it. The twist is this:
I would like the background image to swipeable like a carousel, but I would like the UI elements to stay in place. That is if I swipe the screen, the background image should slide to the side and a new image should replace it. I know about CarouselPage, but it seems to me that it won't do the trick, since a Page can have only one child which it replaces on swipe, meaning that the UI elements would be descendants of the CarouselPage and therefore would also be animated.
I am guessing I need some sort of custom renderer here, but how should I go about designing it? Should it be one fullscreen Image control replaced be another fullscreen Image control with the UI elements on top of it? And how can I do this? Or is there an all together better approach?
I am developing for iOS and Android using Xamarin.Forms.
Thanks in advance.

Answer 1

I don't like repeating myself much, and I think that multiple layers of actionable items can lead to confusion, but the problems appeals to me and I can see a niche for this kind of UI, so here's my take on your question.
Let's assume this is the (Xamarin.Forms.)Page you want to render with a custom carousel background:
public class FunkyPage : ContentPage
{
public IList<string> ImagePaths { get; set; }
public FunkyPage ()
{
Content = new StackLayout {
VerticalOptions = LayoutOptions.Center,
HorizontalOptions = LayoutOptions.Center,
Spacing = 12,
Children = {
new Label { Text = "Foo" },
new Label { Text = "Bar" },
new Label { Text = "Baz" },
new Label { Text = "Qux" },
}
};
ImagePaths = new List<string> { "red.png", "green.png", "blue.png", "orange.png" };
}
}
The renderer for iOS could look like this:
[assembly: ExportRenderer (typeof (FunkyPage), typeof (FunkyPageRenderer))]
public class FunkyPageRenderer : PageRenderer
{
UIScrollView bgCarousel = new UIScrollView (RectangleF.Empty) {
PagingEnabled = true,
ScrollEnabled=true
};
List<UIImageView> uiimages = new List<UIImageView> ();
protected override void OnElementChanged (VisualElementChangedEventArgs e)
{
foreach (var sub in uiimages)
sub.RemoveFromSuperview ();
uiimages.Clear ();
if (e.NewElement != null) {
var page = e.NewElement as FunkyPage;
foreach (var image in page.ImagePaths) {
var uiimage = new UIImageView (new UIImage (image));
bgCarousel.Add (uiimage);
uiimages.Add (uiimage);
}
}
base.OnElementChanged (e);
}
public override void ViewDidLoad ()
{
Add (bgCarousel);
base.ViewDidLoad ();
}
public override void ViewWillLayoutSubviews ()
{
base.ViewWillLayoutSubviews ();
bgCarousel.Frame = View.Frame;
var origin = 0f;
foreach (var image in uiimages) {
image.Frame = new RectangleF (origin, 0, View.Frame.Width, View.Frame.Height);
origin += View.Frame.Width;
}
bgCarousel.ContentSize = new SizeF (origin, View.Frame.Height);
}
}
This was tested and works. Adding a UIPageControl (the dots) is easy on top of this. Autoscrolling of the background is trivial too.
The process is similar on Android, the overrides are a bit different.