Correct Grid Height When Aspect Fit Image Gets Shrinked (#4990)

- fixes #4933

* Grid size incorrect when using with Image #4990 

* Unit Test for Grid size incorrect when using with Image #4933

* Grid size incorrect when using with Image #4933

* Unit Test for Grid size incorrect when using with Image #4933

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue4493.cs

@@ -0,0 +1,32 @@
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+namespace Xamarin.Forms.Controls.Issues
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 4933, "Grid size incorrect when using with Image", PlatformAffected.All)]
+	public class Issue4493 : TestContentPage // or TestMasterDetailPage, etc ...
+	{
+		protected override void Init()
+		{
+			// Initialize ui here instead of ctor
+			BackgroundColor = Color.Gray;
+			var contentGrid = new Grid
+			{
+				AutomationId = "IssuePageGrid",
+				HorizontalOptions = LayoutOptions.FillAndExpand,
+				VerticalOptions = LayoutOptions.Center,
+				BackgroundColor = Color.Maroon,
+				RowSpacing = 0,
+				RowDefinitions = new RowDefinitionCollection()
+				{
+					new RowDefinition(){Height = GridLength.Auto},
+					new RowDefinition(){Height = 20}
+				}
+			};
+			contentGrid.AddChild(new Image() { Source = "photo.jpg", AutomationId = "IssuePageImage" }, 0, 0);
+			contentGrid.AddChild(new Label() { Text = "test message", BackgroundColor = Color.Blue }, 0, 1);
+			Content = contentGrid;
+		}
+	}
+}

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

@@ -890,6 +890,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Issue4138.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue4314.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue3318.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue4493.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue5172.cs" />
   </ItemGroup>
   <ItemGroup>

Xamarin.Forms.Core.UnitTests/GridTests.cs

@@ -1519,6 +1519,28 @@ namespace Xamarin.Forms.Core.UnitTests
 			Assert.False (invalidated);
 		}
 
+
+		[Test]
+		//https://github.com/xamarin/Xamarin.Forms/issues/4933
+		public void GridHeightCorrectWhenAspectFitImageGetsShrinked()
+		{
+			var contentGrid = new Grid
+			{
+				HorizontalOptions = LayoutOptions.FillAndExpand,
+				VerticalOptions = LayoutOptions.Center,
+				RowDefinitions = new RowDefinitionCollection()
+				{
+					new RowDefinition(){Height = GridLength.Auto}
+				}
+			};
+			//image will have "EVERYTHING IS 100 x 20" size so grid should shrink it and itself to 50x10
+			contentGrid.Children.Add(new Image() { IsPlatformEnabled = true }, 0, 0);
+			var measurement = contentGrid.Measure(50, 100);
+			Assert.AreEqual(50, measurement.Request.Width);
+			Assert.AreEqual(10, measurement.Request.Height);
+		}
+
+
 		// because the constraint is internal, we need this
 		public enum HackLayoutConstraint
 		{

Xamarin.Forms.Core/GridCalc.cs

@@ -374,7 +374,7 @@ namespace Xamarin.Forms
 		void MeasureAndContractStarredColumns(double width, double height, double totalStarsWidth)
 		{
 			double starColWidth;
-			starColWidth = MeasuredStarredColumns();
+			starColWidth = MeasuredStarredColumns(width, height);
 
 			if (!double.IsPositiveInfinity(width) && double.IsPositiveInfinity(height))
 			{
@@ -426,7 +426,7 @@ namespace Xamarin.Forms
 			ContractRowsIfNeeded(height, r => r.Height.IsStar);
 		}
 
-		double MeasuredStarredColumns()
+		double MeasuredStarredColumns(double widthConstraint, double heightConstraint)
 		{
 			double starColWidth;
 			for (var iteration = 0; iteration < 2; iteration++)
@@ -450,7 +450,7 @@ namespace Xamarin.Forms
 								continue;
 							double assignedWidth = GetAssignedColumnWidth(child);
 
-							SizeRequest sizeRequest = child.Measure(double.PositiveInfinity, double.PositiveInfinity, MeasureFlags.IncludeMargins);
+							SizeRequest sizeRequest = child.Measure(widthConstraint, heightConstraint, MeasureFlags.IncludeMargins);
 							actualWidth = Math.Max(actualWidth, sizeRequest.Request.Width - assignedWidth - (GetColumnSpan(child) - 1) * ColumnSpacing);
 							minimumWidth = Math.Max(minimumWidth, sizeRequest.Minimum.Width - assignedWidth - (GetColumnSpan(child) - 1) * ColumnSpacing);
 						}