From 058c5e18a424fcdbc5b29741ac198c1cfc17cfb3 Mon Sep 17 00:00:00 2001
From: Huo Yaoyuan <huoyaoyuan@hotmail.com>
Date: Sat, 20 May 2017 05:48:40 +0800
Subject: [PATCH] Scrolling support for SectionsContainer.

---
 .../Graphics/Containers/SectionsContainer.cs  | 41 +++++++++++++++----
 1 file changed, 34 insertions(+), 7 deletions(-)

diff --git a/osu.Game/Graphics/Containers/SectionsContainer.cs b/osu.Game/Graphics/Containers/SectionsContainer.cs
index 9c2485c49c..3557a09622 100644
--- a/osu.Game/Graphics/Containers/SectionsContainer.cs
+++ b/osu.Game/Graphics/Containers/SectionsContainer.cs
@@ -4,8 +4,6 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 
@@ -26,10 +24,11 @@ namespace osu.Game.Graphics.Containers
             {
                 if (value == expandableHeader) return;
 
-                scrollContainer.Remove(expandableHeader);
+                Remove(expandableHeader);
                 expandableHeader = value;
                 expandableHeader.Depth = float.MinValue;
-                scrollContainer.Add(expandableHeader);
+                Add(expandableHeader);
+                updateSectionMargin();
             }
         }
 
@@ -40,10 +39,11 @@ namespace osu.Game.Graphics.Containers
             {
                 if (value == fixedHeader) return;
 
-                scrollContainer.Remove(fixedHeader);
+                Remove(fixedHeader);
                 fixedHeader = value;
                 fixedHeader.Depth = float.MinValue / 2;
-                scrollContainer.Add(fixedHeader);
+                Add(fixedHeader);
+                updateSectionMargin();
             }
         }
 
@@ -59,10 +59,25 @@ namespace osu.Game.Graphics.Containers
                     scrollContainer.Remove(section);
 
                 sections = value.ToList();
-                scrollContainer.Add(value);
+                if (sections.Count == 0) return;
+
+                originalSectionMargin = sections[0].Margin;
+                updateSectionMargin();
+                scrollContainer.Add(sections);
             }
         }
 
+        private MarginPadding originalSectionMargin;
+        private void updateSectionMargin()
+        {
+            if (sections.Count == 0) return;
+
+            var newMargin = originalSectionMargin;
+            newMargin.Top += ExpandableHeader?.Height ?? 0 + FixedHeader?.Height ?? 0;
+
+            sections[0].Margin = newMargin;
+        }
+
         public SectionsContainer()
         {
             Add(scrollContainer = new ScrollContainer
@@ -70,5 +85,17 @@ namespace osu.Game.Graphics.Containers
                 RelativeSizeAxes = Axes.Both
             });
         }
+
+        protected override void UpdateAfterChildren()
+        {
+            base.UpdateAfterChildren();
+            if (expandableHeader == null) return;
+
+            float position = scrollContainer.Current;
+            float offset = Math.Max(expandableHeader.Height, position);
+
+            expandableHeader.Y = -offset;
+            fixedHeader.Y = -offset + expandableHeader.Height;
+        }
     }
 }