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[layout] avoid IView[] creation in LayoutExtensions #8250

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Jun 23, 2022
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[layout] avoid IView[] creation in LayoutExtensions #8250

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56 changes: 10 additions & 46 deletions src/Core/src/Handlers/Layout/LayoutExtensions.cs
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Original file line number Diff line number Diff line change
@@ -1,59 +1,23 @@
using System;
using System.Collections.Generic;
using System.Linq;

namespace Microsoft.Maui.Handlers
{
internal static class LayoutExtensions
{
record ViewAndIndex(IView View, int Index);
public static IOrderedEnumerable<IView> OrderByZIndex(this ILayout layout) => layout.OrderBy(v => v.ZIndex);

class ZIndexComparer : IComparer<ViewAndIndex>
{
public int Compare(ViewAndIndex? x, ViewAndIndex? y)
Comment on lines -10 to -12
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It appears that a regular OrderBy() is the same as this logic. Let me know if I'm missing something, thanks!

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Yeah, I only wrote it the hard way because otherwise I'd have to argue with people about the Linq :)

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I found other places where performance matters, that used OrderBy():

https://github.com/dotnet/msbuild/blob/c2ec5c98a76a5496a36025b3f5e790cca6ea3b2f/src/Build/Evaluation/LazyItemEvaluator.cs#L511-L515

This is used when MSBuild evaluates a project, for every type of item group in a build. It would be called when VS loads a project.

{
if (x == null || y == null)
{
return 0;
}

var zIndexCompare = x.View.ZIndex.CompareTo(y.View.ZIndex);

if (zIndexCompare == 0)
{
return x.Index.CompareTo(y.Index);
}

return zIndexCompare;
}
}

static ZIndexComparer s_comparer = new();

public static IView[] OrderByZIndex(this ILayout layout)
public static int GetLayoutHandlerIndex(this ILayout layout, IView view)
{
var count = layout.Count;
var indexedViews = new ViewAndIndex[count];

for (int n = 0; n < count; n++)
switch (layout.Count)
{
indexedViews[n] = new ViewAndIndex(layout[n], n);
case 0:
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I bet this is a huge chunk of the performance gain.

return -1;
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was it returning -1 before ?

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Yep.

case 1:
return view == layout[0] ? 0 : -1;
default:
return layout.OrderByZIndex().IndexOf(view);
}

Array.Sort(indexedViews, s_comparer);

var ordered = new IView[count];

for (int n = 0; n < count; n++)
{
ordered[n] = indexedViews[n].View;
}

return ordered;
}

public static int GetLayoutHandlerIndex(this ILayout layout, IView view)
{
return layout.OrderByZIndex().IndexOf(view);
}
}
}
9 changes: 5 additions & 4 deletions src/Core/tests/UnitTests/Layouts/ZIndexTests.cs
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Original file line number Diff line number Diff line change
@@ -1,5 +1,6 @@
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using Microsoft.Maui.Graphics;
using Microsoft.Maui.Handlers;
using Microsoft.Maui.Primitives;
Expand Down Expand Up @@ -209,7 +210,7 @@ public void ItemsOrderByZIndex()
layout.Add(view0);
layout.Add(view1);

var zordered = layout.OrderByZIndex();
var zordered = layout.OrderByZIndex().ToArray();
Assert.Equal(view1, zordered[0]);
Assert.Equal(view0, zordered[1]);
}
Expand All @@ -228,7 +229,7 @@ public void ZIndexUpdatePreservesAddOrderForEqualZIndexes()
layout.Add(view2);
layout.Add(view3);

var zordered = layout.OrderByZIndex();
var zordered = layout.OrderByZIndex().ToArray();
Assert.Equal(view0, zordered[0]);
Assert.Equal(view1, zordered[1]);
Assert.Equal(view2, zordered[2]);
Expand All @@ -237,7 +238,7 @@ public void ZIndexUpdatePreservesAddOrderForEqualZIndexes()
// Fake an update
view3.ZIndex.Returns(5);

zordered = layout.OrderByZIndex();
zordered = layout.OrderByZIndex().ToArray();
Assert.Equal(view0, zordered[0]);
Assert.Equal(view1, zordered[1]);
Assert.Equal(view2, zordered[2]);
Expand Down Expand Up @@ -267,7 +268,7 @@ public void ZIndexUpdatePreservesAddOrderLotsOfEqualZIndexes()

for (int i = 0; i < iterations; i++)
{
var zordered = layout.OrderByZIndex();
var zordered = layout.OrderByZIndex().ToArray();

for (int n = 0; n < zordered.Length; n++)
{
Expand Down