[UWP] Fixes of calculation of heights in the MasterDetailPage (#2924) Fixes #1648

* [UWP] Fixes of calculation of heights in the MasterDetailPage

* addressing comments

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/GitHub1648.cs

@@ -0,0 +1,63 @@
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+#if UITEST
+using Xamarin.UITest;
+using NUnit.Framework;
+#endif
+
+namespace Xamarin.Forms.Controls.Issues
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 1648, "MasterDetailPage throws ArgumentOutOfRangeException", PlatformAffected.UWP)]
+	public class GitHub1648 : TestNavigationPage
+	{
+		protected override void Init()
+		{
+			Navigation.PushAsync(new MasterDetailPage
+			{
+				Master = new NavigationPage(new ContentPage())
+				{
+					Title = "Master"
+				},
+				Detail = new ContentPage(),
+			});
+		}
+
+		protected override void OnAppearing()
+		{
+			base.OnAppearing();
+			Navigation.PushModalAsync(new SimplePage());
+		}
+
+		class SimplePage : ContentPage
+		{
+			public SimplePage ()
+			{
+				Content = new StackLayout()
+				{
+					Children = {
+						new Label {
+							Text = "Success"
+						},
+						new Button
+						{
+							Text = "Reload",
+							Command = new Command(() => Navigation.PopModalAsync())
+						}
+					}
+				};
+			}
+		}
+
+#if UITEST
+		[Test]
+		public void GitHub1648Test()
+		{
+			RunningApp.WaitForElement("Reload");
+			RunningApp.Tap("Reload");
+			RunningApp.WaitForElement("Success");
+		}
+#endif
+	}
+}

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems

@@ -243,6 +243,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Effects\AttachedStateEffect.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Effects\AttachedStateEffectLabel.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Effects\AttachedStateEffectList.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)GitHub1648.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)GitHub1702.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)GitHub2598.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue1483.cs" />

Xamarin.Forms.Platform.UAP/MasterDetailControl.cs

@@ -109,7 +109,7 @@ namespace Xamarin.Forms.Platform.UWP
 						width -= _masterPresenter.ActualWidth;
 				}
 
-				return new Windows.Foundation.Size(width >= 0 ? width : 0, height);
+				return new Windows.Foundation.Size(Math.Max(width, 0), Math.Max(height, 0));
 			}
 		}
 
@@ -181,7 +181,7 @@ namespace Xamarin.Forms.Platform.UWP
 				else if (_masterPresenter != null)
 					width = _masterPresenter.ActualWidth;
 
-				return new Windows.Foundation.Size(width, height);
+				return new Windows.Foundation.Size(Math.Max(width, 0), Math.Max(height, 0));
 			}
 		}