Xamarin iOS reference in Android project in Xamarin Forms - xamarin.forms

Question

I created a cross platform application using Xamarin. I need to call native functions of iOS and Android platform in my project. Here is the code:
private static Func<IDownloadFile, string> _downloadPath = new Func<IDownloadFile, string>(file =>
{
if (Device.RuntimePlatform == Device.iOS)
{
string fileName = (new NSUrl(file.Url, false)).LastPathComponent;
return Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments), fileName);
}
else if (Device.RuntimePlatform == Device.Android)
{
string fileName = Android.Net.Uri.Parse(file.Url).Path.Split('/').Last();
return Path.Combine(Android.App.Application.Context.GetExternalFilesDir(Android.OS.Environment.DirectoryDownloads).AbsolutePath, fileName);
}
return Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments), "");
});
This is the code from notification plugin https://github.com/thudugala/Plugin.LocalNotification.
The problem is when I use that code the Mono.Android and Xamarin.iOS references are being added to my shared project in Dependencies/Assemblies and then when I try to run application in the release mode there is a reference error - I noticed that in my Android project in bin/Release there is Xamarin.iOS reference but there is no reference in Android project. When I remove that reference from Dependencies/Assemblies and comment native calls in my code everything compiles correctly. I am confused because of this. Is my above code correctly or I need to call native functions in another way?

Answer 1

When using .net Standard the approach taken is using an interface that defines the functionality you want to expose then implement in each platform.
In Shared:
public interface IMyInterface
{
string GetUrlPath(string fileUrl);
}
iOS Implementation:
public class MyClass : IMyInterface
{
public string GetUrlPath(string fileUrl)
{
string fileName = (new NSUrl(file.Url, false)).LastPathComponent;
return Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments), fileName);
}
}
Android Implementation:
public class MyClass : IMyInterface
{
public string GetUrlPath(string fileUrl)
{
string fileName = (new NSUrl(file.Url, false)).LastPathComponent;
return Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments), fileName);
}
}
Then using either Xamarin.Forms DependencyService or any other IoC container you can match the Interface with the correct implementation.
In your shared code you will use the Interface and the implementation picked will be transparent.
This post shows a very complete example of how to do it.