Xamarin: detect page pushed on NavigationRenderer - xamarin

Question

I order to apply some navigationBar properties (like as the background image) for different page, I think to have a condition on my custom NavigationRenderer.
My idea is to have some condition like (in my working code)
public class CustomNavigationRenderer : NavigationRenderer
{
public override void ViewDidLoad()
{
base.ViewDidLoad();
if (pagePushed is 1)
{
NavigationBar.SetBackgroundImage(new UIImage(), UIBarMetrics.Default);
NavigationBar.ShadowImage = new UIImage();
}
else (ahother page){
var img = UIImage.FromBundle("MyImage");
NavigationBar.SetBackgroundImage(img, UIBarMetrics.Default);
}
}
}
that allows me to have at least a condition to apply a different navigation properties. Another way is to have 2 Navigationrenderer class but I think is not possible.
Any idea to how do that?

Answer 1

If you look at the source code for NavigationRenderer here, you will notice there are quite a few methods and callbacks you can take advantage of.
I would suggest you can do something like this:
1) Code for your custom NavigationRenderer (iOS project, you will have to do something similar on Android):
using System.Threading.Tasks;
using MyProject.iOS;
using UIKit;
using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;
[assembly: ExportRenderer(typeof(NavigationPage), typeof(NavRenderer))]
namespace MyProject.iOS
{
public class NavRenderer : NavigationRenderer
{
protected override async Task<bool> OnPushAsync(Page page, bool animated)
{
var result = await base.OnPushAsync(page, animated);
if(result)
{
if (page is IMyPageType1)
{
NavigationBar.SetBackgroundImage(new UIImage(), UIBarMetrics.Default);
NavigationBar.ShadowImage = new UIImage();
}
else if(page is IMyPageType2)
{
var img = UIImage.FromBundle("MyImage");
NavigationBar.SetBackgroundImage(img, UIBarMetrics.Default);
}
}
return result;
}
}
}
2) Based on the code above, you need to add two interfaces. These should be located in the same project / dll where your Pages are located (all your Xamarin.Forms UI):
public interface IMyPageType1
{
}
public interface IMyPageType2
{
}
3) Now everything that's remaining is implement the interfaces on the pages where you need it. For example:
public partial class MyPage1 : ContentPage, IMyPageType1
{
//...
}
From here, possibilities are endless! You can add for example a method to IMyPageType1 that would return a color, and then inside your renderer, once you know the page being pushed is implementing IMyPageType1, you can call the method and get the color to use.