Fix for FlexLayout padding issue (#24195)

* Fix-15991- Fixed the padding issue on FlexLayout by add the padding calculation in the Measure and ArrangeChildren method().

* added UITest - 15991

* Fix-15991- Output images added for android and iOS.

* Fix-15991-Updated test method name.

* Fix-15991-Updated the test image based on the Test method name.

* Fix-15991-Updated test method with scrollView automationID.

* Fix-15991-Output image added for windows.

* Fix-15991-Added Unit test case and removed UI testcase.

* Fix-15991-Modified Unit TestCase FlexLayout.

* Fix-15991-Modified Unit TestCase for FlexLayout.

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

@@ -133,6 +133,74 @@ public void UnconstrainedWidthChildrenHaveWidth()
 			Assert.Equal(100, flexFrame.Width);
 		}
 
+		[Fact]
+		public void FlexLayoutPaddingShouldBeAppliedCorrectly_RowDirection()
+		{
+			// Arrange
+			var padding = 16;
+			var root = new Grid();
+			var flexLayout = new FlexLayout { Padding = padding };
+			var view1 = new TestLabel();
+			var view2 = new TestLabel();
+
+			root.Add(flexLayout);
+			flexLayout.Add(view1 as IView);
+			flexLayout.Add(view2 as IView);
+
+			// Act
+			var measure = flexLayout.CrossPlatformMeasure(1000, 1000);
+			flexLayout.CrossPlatformArrange(new Rect(Point.Zero, measure));
+
+			var view1Frame = flexLayout.Children[0].Frame;
+			var view2Frame = flexLayout.Children[1].Frame;
+
+			var leftPadding = view1Frame.X;
+			var topPadding = view1Frame.Y;
+			var rightPadding = measure.Width - view2Frame.Right;
+			var expectedView1Width = measure.Width - (leftPadding + rightPadding + view2.Width);
+			var expectedView2Width = measure.Width - (leftPadding + rightPadding + view1.Width);
+
+			// Assert
+			Assert.Equal(padding, leftPadding);
+			Assert.Equal(padding, rightPadding);
+			Assert.Equal(padding, topPadding);
+			Assert.Equal(expectedView1Width, view1Frame.Width);
+			Assert.Equal(expectedView2Width, view2Frame.Width);
+		}
+
+		[Fact]
+		public void FlexLayoutPaddingShouldBeAppliedCorrectly_ColumnDirection()
+		{
+			// Arrange
+			var padding = 16;
+			var root = new Grid();
+			var flexLayout = new FlexLayout { Padding = padding, Direction = FlexDirection.Column };
+			var view1 = new TestLabel();
+			var view2 = new TestLabel();
+
+			root.Add(flexLayout);
+			flexLayout.Add(view1 as IView);
+			flexLayout.Add(view2 as IView);
+
+			// Act
+			var measure = flexLayout.CrossPlatformMeasure(1000, 1000);
+			flexLayout.CrossPlatformArrange(new Rect(Point.Zero, measure));
+
+			var view1Frame = flexLayout.Children[0].Frame;
+			var view2Frame = flexLayout.Children[1].Frame;
+
+			var bottomPadding = measure.Height - view2Frame.Bottom;
+			var topPadding = view1Frame.Y;
+			var expectedView1Height = measure.Height - (topPadding + bottomPadding + view2.Height);
+			var expectedView2Height = measure.Height - (topPadding + bottomPadding + view1.Height);
+
+			// Assert
+			Assert.Equal(padding, bottomPadding);
+			Assert.Equal(view2.Height, view2Frame.Height);
+			Assert.Equal(expectedView1Height, view1Frame.Height);
+			Assert.Equal(expectedView2Height, view2Frame.Height);
+		}
+
 		[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);
 		}