[Shell] Apply Query string parameters even if they aren't present and correctly apply them to nested pages (#6695)

* apply query string parameters if they aren't there
- apply query string parameters correctly to nested pages

* Update Xamarin.Forms.Core/Shell/Shell.cs

Co-Authored-By: Stephane Delcroix <stephane@delcroix.org>
fixes #6543

Xamarin.Forms.Core.UnitTests/ShellTestBase.cs

@@ -42,7 +42,11 @@ namespace Xamarin.Forms.Core.UnitTests
 		[QueryProperty("SomeQueryParameter", "SomeQueryParameter")]
 		public class ShellTestPage : ContentPage
 		{
-			public string SomeQueryParameter { get; set; }
+			public string SomeQueryParameter
+			{
+				get;
+				set;
+			}
 		}
 
 		protected ShellItem CreateShellItem(TemplatedPage page = null, bool asImplicit = false, string shellContentRoute = null, string shellSectionRoute = null, string shellItemRoute = null)

Xamarin.Forms.Core.UnitTests/ShellTests.cs

@@ -220,6 +220,64 @@ namespace Xamarin.Forms.Core.UnitTests
 		}
 
 
+		[Test]
+		public async Task NavigationWithQueryStringThenWithoutQueryString()
+		{
+			var shell = new Shell();
+
+			var one = new ShellItem { Route = "one" };
+			var two = new ShellItem { Route = "two" };
+
+			var tabone = MakeSimpleShellSection("tabone", "content");
+			var tabfour = MakeSimpleShellSection("tabfour", "content", null);
+
+			one.Items.Add(tabone);
+			two.Items.Add(tabfour);
+
+			shell.Items.Add(one);
+			shell.Items.Add(two);
+
+			ShellTestPage pagetoTest = new ShellTestPage();
+			await shell.GoToAsync(new ShellNavigationState($"//two/tabfour/content?{nameof(ShellTestPage.SomeQueryParameter)}=1234"));
+			two.CurrentItem.CurrentItem.ContentTemplate = new DataTemplate(() =>
+			{
+				pagetoTest = new ShellTestPage();
+				pagetoTest.BindingContext = pagetoTest;
+				return pagetoTest;
+			});
+
+
+			await shell.GoToAsync(new ShellNavigationState($"//one/tabone/content"));
+			await shell.GoToAsync(new ShellNavigationState($"//two/tabfour/content"));
+
+			var page = (two.CurrentItem.CurrentItem as IShellContentController).GetOrCreateContent();
+			Assert.AreEqual(null, (page as ShellTestPage).SomeQueryParameter);
+		}
+
+
+		[Test]
+		public async Task NavigationBetweenShellContentsPassesQueryString()
+		{
+			var shell = new Shell();
+
+			var item = CreateShellItem(shellSectionRoute: "section2");
+			var content = CreateShellContent(shellContentRoute: "content");
+			item.Items[0].Items.Add(content);
+
+			Routing.RegisterRoute("details", typeof(ShellTestPage));
+
+			shell.Items.Add(item);
+
+
+			await shell.GoToAsync(new ShellNavigationState($"//section2/details?{nameof(ShellTestPage.SomeQueryParameter)}=1234"));
+			await shell.GoToAsync(new ShellNavigationState($"//content?{nameof(ShellTestPage.SomeQueryParameter)}=1234"));
+			await shell.GoToAsync(new ShellNavigationState($"//section2/details?{nameof(ShellTestPage.SomeQueryParameter)}=4321"));
+
+			var testPage = (shell.CurrentItem.CurrentItem as IShellSectionController).PresentedPage as ShellTestPage;
+			Assert.AreEqual("4321", testPage.SomeQueryParameter);
+		}
+
+
 		[Test]
 		public async Task NavigationWithQueryStringAndNoDataTemplate()
 		{
@@ -239,7 +297,6 @@ namespace Xamarin.Forms.Core.UnitTests
 
 			await shell.GoToAsync(new ShellNavigationState($"//two/tabfour/content?{nameof(ShellTestPage.SomeQueryParameter)}=1234"));
 			Assert.AreEqual("1234", (two.CurrentItem.CurrentItem.Content as ShellTestPage).SomeQueryParameter);
-
 		}
 
 		[Test]

Xamarin.Forms.Core/Shell/Shell.cs

@@ -449,9 +449,6 @@ namespace Xamarin.Forms
 
 		internal static void ApplyQueryAttributes(Element element, IDictionary<string, string> query, bool isLastItem)
 		{
-			if (query.Count == 0)
-				return;
-
 			string prefix = "";
 			if (!isLastItem)
 			{
@@ -487,7 +484,7 @@ namespace Xamarin.Forms
 				filteredQuery.Add(key, q.Value);
 			}
 
-			if (baseShellItem != null)
+			if (baseShellItem is ShellContent)
 				baseShellItem.ApplyQueryAttributes(filteredQuery);
 			else if (isLastItem)
 				element.SetValue(ShellContent.QueryAttributesProperty, query);

Xamarin.Forms.Core/Shell/ShellItem.cs

@@ -46,7 +46,7 @@ namespace Xamarin.Forms
 			var shellSection = request.Request.Section;
 
 			if (shellSection == null)
-				return Task.FromResult(true);
+				shellSection = Items[0];
 
 			Shell.ApplyQueryAttributes(shellSection, queryData, request.Request.Content == null);
 

Xamarin.Forms.Core/Shell/ShellSection.cs

@@ -72,7 +72,7 @@ namespace Xamarin.Forms
 			ShellContent shellContent = request.Request.Content;
 
 			if (shellContent == null)
-				return Task.FromResult(true);
+				shellContent = Items[0];
 
 			if (request.Request.GlobalRoutes.Count > 0)
 			{