Xamarin.Forms の MasterDetailPage の左上ボタンをカスタマイズする Effect(iOSのみ)

CustomBackButtonMasterDetailEffect.cs

using System;
using System.Collections.Generic;
using System.Linq;
using UIKit;
using NavigationSample.iOS;
using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;

[assembly: ResolutionGroupName("mycompany")]
[assembly: ExportEffect(typeof(CustomBackButtonMasterDetailEffect), "CustomBackButtonMasterDetailEffect")]
namespace NavigationSample.iOS
{
	public class CustomBackButtonMasterDetailEffect : PlatformEffect
	{
		protected override void OnAttached()
		{
			var page = Element as MasterDetailPage;
			NavigationPage.SetHasBackButton(page, false);
			page.Appearing += Page_Appearing;
		}

		protected override void OnDetached()
		{
			var page = Element as MasterDetailPage;
			page.Appearing -= Page_Appearing;
		}

		void Page_Appearing(object sender, EventArgs e)
		{
			var vc = GetParentViewController();
			var page = Element as MasterDetailPage;

			var navigationItem = vc.NavigationController.TopViewController.NavigationItem;
			navigationItem.LeftBarButtonItems = new UIBarButtonItem[] 
			{ 
				new UIBarButtonItem("AAA", UIBarButtonItemStyle.Plain, (s, _) => { page.IsPresented = !page.IsPresented; }) 
			};
		}

		UIViewController GetParentViewController()
		{
			UIResponder responder = this.Container;
			while ((responder = responder.NextResponder) != null)
			{
				if (responder is UIViewController)
				{
					return (UIViewController)responder;
				}
			}
			return null;
		}

	}
}

こうなる↓

thanks for

• Navigation Bar left Toolbar button — Xamarin Forums