[WinRT/UWP] Adjust margin for centered Slider (#604)

1 files changed, 20 insertions, 0 deletions

diff --git a/Xamarin.Forms.Platform.WinRT/SliderRenderer.cs b/Xamarin.Forms.Platform.WinRT/SliderRenderer.cs
index ee7a8adc..cf188f15 100644
--- a/Xamarin.Forms.Platform.WinRT/SliderRenderer.cs
+++ b/Xamarin.Forms.Platform.WinRT/SliderRenderer.cs
@@ -1,5 +1,6 @@
 using System;
 using System.ComponentModel;
+using Windows.UI.Xaml;
 using Windows.UI.Xaml.Controls.Primitives;
 
 #if WINDOWS_UWP
@@ -24,6 +25,25 @@ namespace Xamarin.Forms.Platform.WinRT
 					SetNativeControl(slider);
 
 					slider.ValueChanged += OnNativeValueCHanged;
+
+					// Even when using Center/CenterAndExpand, a Slider has an oddity where it looks
+					// off-center in its layout by a smidge. The default templates are slightly different
+					// between 8.1/UWP; the 8.1 rows are 17/Auto/32 and UWP are 18/Auto/18. The value of
+					// the hardcoded 8.1 rows adds up to 49 (when halved is 24.5) and UWP are 36 (18). Using
+					// a difference of about 6 pixels to correct this oddity seems to make them both center
+					// more correctly.
+					//
+					// The VerticalAlignment needs to be set as well since a control would not actually be
+					// centered if a larger HeightRequest is set.
+					if (Element.VerticalOptions.Alignment == LayoutAlignment.Center && Control.Orientation == Windows.UI.Xaml.Controls.Orientation.Horizontal)
+					{
+						Control.VerticalAlignment = VerticalAlignment.Center;
+#if WINDOWS_UWP
+						slider.Margin = new Windows.UI.Xaml.Thickness(0, 7, 0, 0);
+#else
+						slider.Margin = new Windows.UI.Xaml.Thickness(0, 13, 0, 0);
+#endif
+					}
 				}
 
 				double stepping = Math.Min((e.NewElement.Maximum - e.NewElement.Minimum) / 10, 1);