Xamarin bug happens when linker is set to "Link All". Can't use DependencyService - xamarin

Question

Right now, I have to have my linker set to "Link All" in order to submit to the App Store because of the deprecated UIWebView. While doing this, I had to add [Preserve(AllMembers = true)] to my DataStores to make them work this way, but then I ran into this issue.
The following line will return null:
var dp = DependencyService.Get<ITextMeter>();
After looking into the solution, it seemed the best answer would be to add the following line into the AppDelegate:
DependencyService.Register<ITextMeter, TextMeterImplementation>();
Once I did that, I started receiving this exception:
DependencyService: System.MissingMethodException: Default constructor not found for [Interface]
https://forums.xamarin.com/discussion/71072/dependencyservice-system-missingmethodexception-default-constructor-not-found-for-interface
I just want to find a working solution that will allow everything to work with the linker set to "Link All". Thanks in advance.
ITextMeter:
using System;
using Xamarin.Forms.Internals;
namespace RedSwipe.Services
{
public interface ITextMeter
{
double MeasureTextSize(string text, double width, double fontSize, string fontName = null);
}
}
TextMeterImplementation:
using System.Drawing;
using Foundation;
using RedSwipe.iOS.Services;
using RedSwipe.Services;
using UIKit;
[assembly: Xamarin.Forms.Dependency(typeof(TextMeterImplementation))]
namespace RedSwipe.iOS.Services
{
public class TextMeterImplementation : ITextMeter
{
public double MeasureTextSize(string text, double width, double fontSize, string fontName = null)
{
var nsText = new NSString(text);
var boundSize = new SizeF((float)width, float.MaxValue);
var options = NSStringDrawingOptions.UsesFontLeading | NSStringDrawingOptions.UsesLineFragmentOrigin;
if (fontName == null)
{
fontName = "HelveticaNeue";
}
var attributes = new UIStringAttributes
{
Font = UIFont.FromName(fontName, (float)fontSize)
};
var sizeF = nsText.GetBoundingRect(boundSize, options, attributes, null).Size;
//return new Xamarin.Forms.Size((double)sizeF.Width, (double)sizeF.Height);
return (double)sizeF.Height;
}
}
}

Answer 1

Add this [Preserve (AllMembers = true)] in your TextMeterImplementation before class implementation.
Your code would be like:
using System.Drawing;
using Foundation;
using RedSwipe.iOS.Services;
using RedSwipe.Services;
using UIKit;
using Xamarin.Forms.Internals; // Add This import
[assembly: Xamarin.Forms.Dependency(typeof(TextMeterImplementation))]
namespace RedSwipe.iOS.Services
{
[Preserve (AllMembers = true)]
public class TextMeterImplementation : ITextMeter
{
public double MeasureTextSize(string text, double width, double fontSize, string fontName = null)
{
var nsText = new NSString(text);
var boundSize = new SizeF((float)width, float.MaxValue);
var options = NSStringDrawingOptions.UsesFontLeading | NSStringDrawingOptions.UsesLineFragmentOrigin;
if (fontName == null)
{
fontName = "HelveticaNeue";
}
var attributes = new UIStringAttributes
{
Font = UIFont.FromName(fontName, (float)fontSize)
};
var sizeF = nsText.GetBoundingRect(boundSize, options, attributes, null).Size;
//return new Xamarin.Forms.Size((double)sizeF.Width, (double)sizeF.Height);
return (double)sizeF.Height;
}
}
}