ContentPageRenderer.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection;
using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;
using UIKit;
using MyAppName.iOS.Renderers;

[assembly: ExportRenderer(typeof(ContentPage), typeof(ContentPageRenderer))]
namespace MyAppName.iOS.Renderers
{
  /// <summary>
  /// Custom renderer for ContentPage that allows for action buttons to be on the left or the right hand side (ex: a modal with cancel and done buttons)
  /// ToolbarItems need to have Priority set to 0 to show on the left, 1 to show on the right (ref: https://gist.github.com/alexlau811/f1fff9e726333e6b4a2f)
  /// </summary>
  public class ContentPageRenderer : PageRenderer
  {
    public override void ViewWillAppear(bool animated)
    {
      base.ViewWillAppear(animated);

      var contentPage = this.Element as ContentPage;
      if (contentPage == null || NavigationController == null)
        return;

      var itemsInfo = contentPage.ToolbarItems;

      var navigationItem = this.NavigationController.TopViewController.NavigationItem;
      var leftNativeButtons = (navigationItem.LeftBarButtonItems ?? new UIBarButtonItem[] { }).ToList();
      var rightNativeButtons = (navigationItem.RightBarButtonItems ?? new UIBarButtonItem[] { }).ToList();

      var newLeftButtons = new UIBarButtonItem[] { }.ToList();
      var newRightButtons = new UIBarButtonItem[] { }.ToList();

      rightNativeButtons.ForEach(nativeItem =>
      {
        // [Hack] Get Xamarin private field "item"
        var field = nativeItem.GetType().GetField("_item", BindingFlags.NonPublic | BindingFlags.Instance);
        if (field == null)
          return;

        var info = field.GetValue(nativeItem) as ToolbarItem;
        if (info == null)
          return;

        if (info.Priority == 0)
          newLeftButtons.Add(nativeItem);
        else
          newRightButtons.Add(nativeItem);
      });
      
      leftNativeButtons.ForEach(nativeItem =>
      {
        newLeftButtons.Add(nativeItem);
      });      

      navigationItem.RightBarButtonItems = newRightButtons.ToArray();
      navigationItem.LeftBarButtonItems = newLeftButtons.ToArray();
    }
  }
}

@buchatsky
I am trying to do the same thing with Tabbed page. Aren't you supposed to use
var page = this.Element as TabbedPage;
instead of ContentPage.
Moreover I have only two items in toolbar and I want to move the first one to left and want to keep the second one to right.
Can you please post your complete code?

Cheers

Thank you so much, it worked! but any idea how to do this for android?

Super helpful. Thank you!

I would suggest to make the priority check respond to Priority="-1" instead of 0 because otherwise it will move the first toolbar element always to the left even on pages where you don't intend to.

any solution for duplicated items when using tabbedpage

This seems broken on the latest version of Xamarin.Forms (3.2.0.839982), Xamarin.iOS (12.0.0.15). This was working for me before upgrading. It appears that it can't find the private field "item" anymore.