Refactor ModSection and ModIcon to avoid null mods.

osu.Game/Overlays/Mods/ModButton.cs

@@ -19,7 +19,11 @@ using System.Linq;
 
 namespace osu.Game.Overlays.Mods
 {
-    public class ModButton : FillFlowContainer
+
+    /// <summary>
+    /// Represents a clickable button which can cycle through one of more mods.
+    /// </summary>
+    public class ModButton : ModButtonEmpty
     {
         private ModIcon foregroundIcon { get; set; }
         private readonly SpriteText text;
@@ -116,7 +120,7 @@ namespace osu.Game.Overlays.Mods
 
         // the mods from Mod, only multiple if Mod is a MultiMod
 
-        public Mod SelectedMod => Mods.ElementAtOrDefault(selectedIndex);
+        public override Mod SelectedMod => Mods.ElementAtOrDefault(selectedIndex);
 
         [BackgroundDependencyLoader]
         private void load(AudioManager audio)
@@ -198,13 +202,8 @@ namespace osu.Game.Overlays.Mods
             buttonColour = foregroundIcon.Colour;
         }
 
-        public ModButton(Mod m)
+        public ModButton(Mod mod)
         {
-            Direction = FillDirection.Vertical;
-            Spacing = new Vector2(0f, -5f);
-            Size = new Vector2(100f);
-            AlwaysPresent = true;
-
             Children = new Drawable[]
             {
                 new Container
@@ -224,13 +223,14 @@ namespace osu.Game.Overlays.Mods
                 },
                 text = new OsuSpriteText
                 {
+                    Y = 75,
                     Origin = Anchor.TopCentre,
                     Anchor = Anchor.TopCentre,
                     TextSize = 18,
                 },
             };
 
-            Mod = m;
+            Mod = mod;
         }
     }
 }

osu.Game/Overlays/Mods/ModButtonEmpty.cs

@@ -0,0 +1,23 @@
+// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using OpenTK;
+using osu.Framework.Graphics.Containers;
+using osu.Game.Rulesets.Mods;
+
+namespace osu.Game.Overlays.Mods
+{
+    /// <summary>
+    /// A mod button used exclusively for providing an empty space the size of a mod button.
+    /// </summary>
+    public class ModButtonEmpty : Container
+    {
+        public virtual Mod SelectedMod => null;
+
+        public ModButtonEmpty()
+        {
+            Size = new Vector2(100f);
+            AlwaysPresent = true;
+        }
+    }
+}

osu.Game/Overlays/Mods/ModSection.cs

@@ -11,6 +11,8 @@ using osu.Framework.Input;
 using osu.Game.Graphics.Sprites;
 using osu.Game.Rulesets.Mods;
 using System;
+using System.Linq;
+using System.Collections.Generic;
 
 namespace osu.Game.Overlays.Mods
 {
@@ -18,7 +20,7 @@ namespace osu.Game.Overlays.Mods
     {
         private readonly OsuSpriteText headerLabel;
 
-        public FillFlowContainer<ModButton> ButtonsContainer { get; }
+        public FillFlowContainer<ModButtonEmpty> ButtonsContainer { get; }
 
         public Action<Mod> Action;
         protected abstract Key[] ToggleKeys { get; }
@@ -36,27 +38,30 @@ namespace osu.Game.Overlays.Mods
             }
         }
 
-        private ModButton[] buttons = { };
+        public IEnumerable<Mod> SelectedMods => buttons.Select(b => b.SelectedMod).Where(m => m != null);
-        public ModButton[] Buttons
+
+        public IEnumerable<Mod> Mods
         {
-            get
-            {
-                return buttons;
-            }
             set
             {
-                if (value == buttons) return;
+                var modContainers = value.Select(m =>
-                buttons = value;
-
-                foreach (ModButton button in value)
                 {
-                    button.SelectedColour = selectedColour;
+                    if (m == null)
-                    button.Action = Action;
+                        return new ModButtonEmpty();
+                    else
+                        return new ModButton(m)
+                        {
+                            SelectedColour = selectedColour,
+                            Action = Action,
+                        };
+                }).ToArray();
+
+                ButtonsContainer.Children = modContainers;
+                buttons = modContainers.OfType<ModButton>().ToArray();
+            }
         }
 
-                ButtonsContainer.Children = value;
+        private ModButton[] buttons = { };
-            }
-        }
 
         private Color4 selectedColour = Color4.White;
         public Color4 SelectedColour
@@ -71,17 +76,15 @@ namespace osu.Game.Overlays.Mods
                 selectedColour = value;
 
                 foreach (ModButton button in buttons)
-                {
                     button.SelectedColour = value;
             }
         }
-        }
 
         protected override bool OnKeyDown(InputState state, KeyDownEventArgs args)
         {
             var index = Array.IndexOf(ToggleKeys, args.Key);
-            if (index > -1 && index < Buttons.Length)
+            if (index > -1 && index < buttons.Length)
-                Buttons[index].SelectNext();
+                buttons[index].SelectNext();
 
             return base.OnKeyDown(state, args);
         }
@@ -89,7 +92,17 @@ namespace osu.Game.Overlays.Mods
         public void DeselectAll()
         {
             foreach (ModButton button in buttons)
+                button.Deselect();
+        }
+
+        public void DeselectTypes(Type[] modTypes)
         {
+            foreach (var button in buttons)
+            {
+                Mod selected = button.SelectedMod;
+                if (selected == null) continue;
+                foreach (Type type in modTypes)
+                    if (type.IsInstanceOfType(selected))
                         button.Deselect();
             }
         }
@@ -107,7 +120,7 @@ namespace osu.Game.Overlays.Mods
                     Position = new Vector2(0f, 0f),
                     Font = @"Exo2.0-Bold"
                 },
-                ButtonsContainer = new FillFlowContainer<ModButton>
+                ButtonsContainer = new FillFlowContainer<ModButtonEmpty>
                 {
                     AutoSizeAxes = Axes.Both,
                     Origin = Anchor.BottomLeft,

osu.Game/Overlays/Mods/ModSelectOverlay.cs

@@ -44,7 +44,7 @@ namespace osu.Game.Overlays.Mods
             var instance = newRuleset.CreateInstance();
 
             foreach (ModSection section in modSectionsContainer.Children)
-                section.Buttons = instance.GetModsFor(section.ModType).Select(m => new ModButton(m)).ToArray();
+                section.Mods = instance.GetModsFor(section.ModType);
             refreshSelectedMods();
         }
 
@@ -103,14 +103,7 @@ namespace osu.Game.Overlays.Mods
         {
             if (modTypes.Length == 0) return;
             foreach (ModSection section in modSectionsContainer.Children)
-                foreach (ModButton button in section.Buttons)
+                section.DeselectTypes(modTypes);
-                {
-                    Mod selected = button.SelectedMod;
-                    if (selected == null) continue;
-                    foreach (Type type in modTypes)
-                        if (type.IsInstanceOfType(selected))
-                            button.Deselect();
-                }
         }
 
         private void modButtonPressed(Mod selectedMod)
@@ -122,7 +115,7 @@ namespace osu.Game.Overlays.Mods
 
         private void refreshSelectedMods()
         {
-            SelectedMods.Value = modSectionsContainer.Children.SelectMany(s => s.Buttons.Select(x => x.SelectedMod).Where(x => x != null)).ToArray();
+            SelectedMods.Value = modSectionsContainer.Children.SelectMany(s => s.SelectedMods).ToArray();
 
             double multiplier = 1.0;
             bool ranked = true;

osu.Game/Rulesets/UI/ModIcon.cs

@@ -1,6 +1,7 @@
 // Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
 // Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
 
+using System;
 using OpenTK.Graphics;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
@@ -42,6 +43,8 @@ namespace osu.Game.Rulesets.UI
 
         public ModIcon(Mod mod)
         {
+            if (mod == null) throw new ArgumentNullException(nameof(mod));
+
             Children = new Drawable[]
             {
                 background = new TextAwesome
@@ -59,7 +62,7 @@ namespace osu.Game.Rulesets.UI
                     Anchor = Anchor.Centre,
                     Colour = OsuColour.Gray(84),
                     TextSize = 20,
-                    Icon = (mod != null) ? mod.Icon : FontAwesome.fa_question,
+                    Icon = mod.Icon
                 },
             };
 
@@ -74,7 +77,7 @@ namespace osu.Game.Rulesets.UI
 
         private Color4 getBackgroundColourFromMod(Mod mod)
         {
-            switch (mod?.Type)
+            switch (mod.Type)
             {
                 case ModType.DifficultyIncrease:
                     return OsuColour.FromHex(@"ffcc22");

osu.Game/osu.Game.csproj

@@ -391,6 +391,7 @@
     <Compile Include="Screens\Play\Pause\PauseProgressGraph.cs" />
     <Compile Include="Overlays\Mods\ModSelectOverlay.cs" />
     <Compile Include="Rulesets\Mods\Mod.cs" />
+    <Compile Include="Overlays\Mods\ModButtonEmpty.cs" />
     <Compile Include="Overlays\Mods\ModButton.cs" />
     <Compile Include="Rulesets\UI\ModIcon.cs" />
     <Compile Include="Overlays\Mods\ModSection.cs" />