Fix for FlexLayout padding issue

src/Controls/tests/Core.UnitTests/Layouts/FlexLayoutTests.cs

@@ -33,6 +33,14 @@ protected override Size MeasureOverride(double widthConstraint, double heightCon
 			}
 		}
 
+		class TestBoxView : BoxView
+		{
+			protected override Size MeasureOverride(double widthConstraint, double heightConstraint)
+			{
+				return new Size(40, 20);
+			}
+		}
+
 		[Fact]
 		public void FlexLayoutMeasuresImagesUnconstrained()
 		{
@@ -133,6 +141,34 @@ public void UnconstrainedWidthChildrenHaveWidth()
 			Assert.Equal(100, flexFrame.Width);
 		}
 
+		[Fact]
+		public void FlexLayoutPaddingShouldBeAppliedCorrectly()
+		{
+			var padding = 16;
+			var root = new VerticalStackLayout();
+
+			var boxView = new TestBoxView
+			{
+				Color = Colors.Red
+			};
+
+			var layout = new FlexLayout
+			{
+				Direction = FlexDirection.Column, 
+				BackgroundColor = Colors.LightGreen,
+				Padding = new Thickness(padding),
+				HeightRequest = 500,
+				WidthRequest = 500,
+				Children = { boxView }
+			};
+			root.Add(layout);
+			var measure = layout.CrossPlatformMeasure(500, 500);
+			layout.CrossPlatformArrange(new Rect(Point.Zero, measure));
+
+			var frame = layout.Children[0].Frame;
+			Assert.Equal(padding, frame.X);
+		}
+
 		[Theory]
 		[InlineData(double.PositiveInfinity, 400, FlexDirection.RowReverse)]
 		[InlineData(double.PositiveInfinity, 400, FlexDirection.Row)]

src/Core/src/Layouts/FlexLayoutManager.cs

@@ -15,7 +15,14 @@ public FlexLayoutManager(IFlexLayout flexLayout)
 
 		public Size ArrangeChildren(Rect bounds)
 		{
-			FlexLayout.Layout(bounds.Width, bounds.Height);
+			var padding = FlexLayout.Padding;
+
+			double top = padding.Top + bounds.Top;
+			double left = padding.Left + bounds.Left;
+			double availableWidth = bounds.Width - padding.HorizontalThickness;
+			double availableHeight = bounds.Height - padding.VerticalThickness;
+
+			FlexLayout.Layout(availableWidth, availableHeight);
 
 			foreach (var child in FlexLayout)
 			{
@@ -25,7 +32,8 @@ public Size ArrangeChildren(Rect bounds)
 					|| double.IsNaN(frame.Width)
 					|| double.IsNaN(frame.Height))
 					throw new Exception("something is deeply wrong");
-				frame = frame.Offset(bounds.Left, bounds.Top);
+
+				frame = frame.Offset(left, top);
 				child.Arrange(frame);
 			}
 
@@ -34,10 +42,15 @@ public Size ArrangeChildren(Rect bounds)
 
 		public Size Measure(double widthConstraint, double heightConstraint)
 		{
+			var padding = FlexLayout.Padding;
+
+			var availableWidth = widthConstraint - padding.HorizontalThickness;
+			var availableHeight = heightConstraint - padding.VerticalThickness;
+
 			double measuredHeight = 0;
 			double measuredWidth = 0;
 
-			FlexLayout.Layout(widthConstraint, heightConstraint);
+			FlexLayout.Layout(availableWidth, availableHeight);
 
 			foreach (var child in FlexLayout)
 			{
@@ -51,8 +64,11 @@ public Size Measure(double widthConstraint, double heightConstraint)
 				measuredWidth = Math.Max(measuredWidth, frame.Right);
 			}
 
-			var finalHeight = LayoutManager.ResolveConstraints(heightConstraint, FlexLayout.Height, measuredHeight, FlexLayout.MinimumHeight, FlexLayout.MaximumHeight);
-			var finalWidth = LayoutManager.ResolveConstraints(widthConstraint, FlexLayout.Width, measuredWidth, FlexLayout.MinimumWidth, FlexLayout.MaximumWidth);
+			var finalHeight = LayoutManager.ResolveConstraints(heightConstraint, FlexLayout.Height, measuredHeight + padding.VerticalThickness,
+				FlexLayout.MinimumHeight, FlexLayout.MaximumHeight);
+
+			var finalWidth = LayoutManager.ResolveConstraints(widthConstraint, FlexLayout.Width, measuredWidth + padding.HorizontalThickness,
+				FlexLayout.MinimumWidth, FlexLayout.MaximumWidth);
 
 			return new Size(finalWidth, finalHeight);
 		}