[Shell] fixes navigate to a relative URI (#4977)

Xamarin.Forms.Core.UnitTests/ShellTests.cs

@@ -127,7 +127,60 @@ namespace Xamarin.Forms.Core.UnitTests
 			Assert.That(shell.CurrentState.Location.ToString(), Is.EqualTo("app:///s/two/tabfour/content/"));
 		}
 
+		[Test]
+		public async Task RelativeGoTo()
+		{
+			var shell = new Shell
+			{
+				Route = "s"
+			};
 
+			var one = new ShellItem { Route = "one" };
+			var two = new ShellItem { Route = "two" };
+
+			var tab11 = MakeSimpleShellSection("tab11", "content");
+			var tab12 = MakeSimpleShellSection("tab12", "content");
+			var tab21 = MakeSimpleShellSection("tab21", "content");
+			var tab22 = MakeSimpleShellSection("tab22", "content");
+			var tab23 = MakeSimpleShellSection("tab23", "content");
+
+			one.Items.Add(tab11);
+			one.Items.Add(tab12);
+
+			two.Items.Add(tab21);
+			two.Items.Add(tab22);
+			two.Items.Add(tab23);
+
+			shell.Items.Add(one);
+			shell.Items.Add(two);
+
+			await shell.GoToAsync("app:///s/two/tab21/");
+
+			await shell.GoToAsync("/tab22");
+			Assert.That(shell.CurrentState.Location.ToString(), Is.EqualTo("app:///s/two/tab22/content/"));
+
+			await shell.GoToAsync("tab21");
+			Assert.That(shell.CurrentState.Location.ToString(), Is.EqualTo("app:///s/two/tab21/content/"));
+
+			await shell.GoToAsync("/tab23");
+			Assert.That(shell.CurrentState.Location.ToString(), Is.EqualTo("app:///s/two/tab23/content/"));
+
+			await shell.GoToAsync("../one/tab11");
+			Assert.That(shell.CurrentState.Location.ToString(), Is.EqualTo("app:///s/one/tab11/content/"));
+
+			await shell.GoToAsync("/eee/hm../../../../two/../one/../two/tab21");
+			Assert.That(shell.CurrentState.Location.ToString(), Is.EqualTo("app:///s/two/tab21/content/"));
+
+			await shell.GoToAsync(new ShellNavigationState("../one/tab11"));
+			Assert.That(shell.CurrentState.Location.ToString(), Is.EqualTo("app:///s/one/tab11/content/"));
+
+			await shell.GoToAsync(new ShellNavigationState($"../two/tab23/content?{nameof(ShellTestPage.SomeQueryParameter)}=1234"));
+			Assert.That(shell.CurrentState.Location.ToString(), Is.EqualTo("app:///s/two/tab23/content/"));
+			Assert.AreEqual("1234", (two.CurrentItem.CurrentItem.Content as ShellTestPage).SomeQueryParameter);
+
+			await shell.GoToAsync(new ShellNavigationState($"../one/tab11#fragment"));
+			Assert.That(shell.CurrentState.Location.ToString(), Is.EqualTo("app:///s/one/tab11/content/"));
+		}
 
 		[Test]
 		public async Task NavigationWithQueryStringWhenPageMatchesBindingContext()

Xamarin.Forms.Core/Shell/Shell.cs

@@ -6,6 +6,7 @@ using System.Linq;
 using System.Reflection;
 using System.Runtime.CompilerServices;
 using System.Text;
+using System.Text.RegularExpressions;
 using System.Threading.Tasks;
 using Xamarin.Forms.Internals;
 
@@ -324,6 +325,35 @@ namespace Xamarin.Forms
 
 		public static Shell CurrentShell => Application.Current?.MainPage as Shell;
 
+		Uri GetAbsoluteUri(Uri relativeUri)
+		{
+			if (CurrentItem == null)
+				throw new InvalidOperationException("Relative path is used after selecting Current item.");
+
+			var parseUri = Regex.Match(relativeUri.OriginalString, @"(?<u>.+?)(\?(?<q>.+?))?(#(?<f>.+))?$").Groups;
+			var url = parseUri["u"].Value;
+			var query = parseUri["q"].Value;
+			var fragment = parseUri["f"].Value;
+
+			Element item = CurrentItem;
+			var list = new List<string> { url.Trim('/') };
+			while (item != null)
+			{
+				var route = Routing.GetRoute(item)?.Trim('/');
+				if (string.IsNullOrEmpty(route))
+					break;
+				list.Insert(0, route);
+				item = item.Parent;
+			}
+			var parentUriBuilder = new UriBuilder(RouteScheme)
+			{
+				Path = string.Join("/", list),
+				Query = query,
+				Fragment = fragment
+			};
+			return parentUriBuilder.Uri;
+		}
+
 		public async Task GoToAsync(ShellNavigationState state, bool animate = true)
 		{
 			// FIXME: This should not be none, we need to compute the delta and set flags correctly
@@ -333,7 +363,7 @@ namespace Xamarin.Forms
 
 			_accumulateNavigatedEvents = true;
 
-			var uri = state.Location;
+			var uri = state.Location.IsAbsoluteUri ? state.Location : GetAbsoluteUri(state.Location);
 			var queryString = uri.Query;
 			var queryData = ParseQueryString(queryString);
 			var path = uri.AbsolutePath;

Xamarin.Forms.Core/Shell/ShellNavigationState.cs

@@ -7,7 +7,7 @@ namespace Xamarin.Forms
 		public Uri Location { get; set; }
 
 		public ShellNavigationState() { }
-		public ShellNavigationState(string location) => Location = new Uri(location);
+		public ShellNavigationState(string location) => Location = new Uri(location, UriKind.RelativeOrAbsolute);
 		public ShellNavigationState(Uri location) => Location = location;
 		public static implicit operator ShellNavigationState(Uri uri) => new ShellNavigationState(uri);
 		public static implicit operator ShellNavigationState(string value) => new ShellNavigationState(value);