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Prevent iOS CollectionView size shifts from clearing the cell size cache
Fixes #17890
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42 changes: 42 additions & 0 deletions
42
src/Controls/src/Core/Handlers/Items/iOS/SizeExtensions.cs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,42 @@ | ||
| #nullable disable | ||
| using System; | ||
| using CoreGraphics; | ||
| using Microsoft.Maui.Graphics; | ||
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| namespace Microsoft.Maui.Controls.Handlers.Items | ||
| { | ||
| internal static class SizeExtensions | ||
| { | ||
| const double Tolerance = 0.001; | ||
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| public static bool IsCloseTo(this CGSize sizeA, CGSize sizeB) | ||
| { | ||
| if (Math.Abs(sizeA.Height - sizeB.Height) > Tolerance) | ||
| { | ||
| return false; | ||
| } | ||
|
|
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| if (Math.Abs(sizeA.Width - sizeB.Width) > Tolerance) | ||
| { | ||
| return false; | ||
| } | ||
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| return true; | ||
| } | ||
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| public static bool IsCloseTo(this CGSize sizeA, Size sizeB) | ||
| { | ||
| if (Math.Abs(sizeA.Height - sizeB.Height) > Tolerance) | ||
| { | ||
| return false; | ||
| } | ||
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| if (Math.Abs(sizeA.Width - sizeB.Width) > Tolerance) | ||
| { | ||
| return false; | ||
| } | ||
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| return true; | ||
| } | ||
| } | ||
| } |
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150 changes: 150 additions & 0 deletions
150
src/Controls/tests/DeviceTests/Elements/CollectionView/CollectionViewCacheTests.ios.cs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,150 @@ | ||
| using System.Collections.Generic; | ||
| using System.Threading.Tasks; | ||
| using CoreGraphics; | ||
| using Foundation; | ||
| using Microsoft.Maui.Controls; | ||
| using Microsoft.Maui.Controls.Handlers.Items; | ||
| using UIKit; | ||
| using Xunit; | ||
|
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| namespace Microsoft.Maui.DeviceTests | ||
| { | ||
| public partial class CollectionViewTests | ||
| { | ||
| public class CacheTestCollectionView : CollectionView { } | ||
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| class CacheTestCollectionViewHandler : ReorderableItemsViewHandler<CacheTestCollectionView> | ||
| { | ||
| protected override ItemsViewController<CacheTestCollectionView> CreateController(CacheTestCollectionView itemsView, ItemsViewLayout layout) | ||
| { | ||
| return new CacheTestItemsViewController(itemsView, layout); | ||
| } | ||
| } | ||
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| class CacheTestItemsViewController : ItemsViewController<CacheTestCollectionView> | ||
| { | ||
| protected override bool IsHorizontal { get; } | ||
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| public UICollectionViewDelegateFlowLayout DelegateFlowLayout { get; private set; } | ||
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| public CacheTestItemsViewController(CacheTestCollectionView reorderableItemsView, ItemsViewLayout layout) : base(reorderableItemsView, layout) | ||
| { | ||
| } | ||
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| protected override UICollectionViewDelegateFlowLayout CreateDelegator() | ||
| { | ||
| DelegateFlowLayout = new CacheMissCountingDelegate(ItemsViewLayout, this); | ||
| return DelegateFlowLayout; | ||
| } | ||
| } | ||
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| internal class CacheMissCountingDelegate : ItemsViewDelegator<CacheTestCollectionView, ItemsViewController<CacheTestCollectionView>> | ||
| { | ||
| public int CacheMissCount { get; set; } | ||
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| public CacheMissCountingDelegate(ItemsViewLayout itemsViewLayout, ItemsViewController<CacheTestCollectionView> itemsViewController) : base(itemsViewLayout, itemsViewController) | ||
| { | ||
| } | ||
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| public override CGSize GetSizeForItem(UICollectionView collectionView, UICollectionViewLayout layout, NSIndexPath indexPath) | ||
| { | ||
| var itemSize = base.GetSizeForItem(collectionView, layout, indexPath); | ||
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| if (ViewController.Layout is UICollectionViewFlowLayout flowLayout) | ||
| { | ||
| // This is totally a cheat from a unit-testing perspective; we know how the item size cache | ||
| // functions internally (that it will return the estimated size if the item size is not found in the cache), | ||
| // and we're relying on that for this test. Normally we wouldn't do this, but we need to ensure that further | ||
| // code changes don't break the cache again, and the only observable outside consequence is that the scrolling | ||
| // for the CollectionView becomes "janky". We don't want to rely entirely on human perception of "jankiness" to | ||
| // catch this problem. | ||
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| // If the size comes back as EstimatedItemSize, we'll know that the actual value was not found in the cache. | ||
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| if (itemSize == flowLayout.EstimatedItemSize) | ||
| { | ||
| CacheMissCount += 1; | ||
| } | ||
| } | ||
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| return itemSize; | ||
| } | ||
| } | ||
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| internal class ItemModel | ||
| { | ||
| public int Index { get; set; } | ||
| public double HeightRequest => 40 * (Index + 1); | ||
| } | ||
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| [Fact] | ||
| public async Task EnsureCellSizesAreCached() | ||
| { | ||
| SetupBuilder(); | ||
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| var collectionView = new CacheTestCollectionView() | ||
| { | ||
| // Deliberately choosing a height which will cause rounding issues which can caused pathological | ||
| // sizing/layout loops if handled wrong | ||
| HeightRequest = 654.66666 | ||
| }; | ||
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| var template = new DataTemplate(() => { | ||
| var content = new Label() { Text = "Howdy" }; | ||
| content.SetBinding(VisualElement.HeightRequestProperty, new Binding(nameof(VisualElement.HeightRequest))); | ||
| return content; | ||
| }); | ||
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| // Build up a view model that's got enough items to ensure scrolling and template reuse | ||
| int itemCount = 15; | ||
| var source = new List<ItemModel>(); | ||
| for (int n = 0; n < itemCount; n++) | ||
| { | ||
| source.Add(new ItemModel() { Index = n }); | ||
| } | ||
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| collectionView.ItemTemplate = template; | ||
| collectionView.ItemsSource = source; | ||
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| var frame = collectionView.Frame; | ||
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| await CreateHandlerAndAddToWindow<CacheTestCollectionViewHandler>(collectionView, async handler => | ||
| { | ||
| // Wait until the CollectionView is actually rendering | ||
| await WaitForUIUpdate(frame, collectionView); | ||
| // Tell it to scroll to the bottom (and give it time to do so) | ||
| collectionView.ScrollTo(itemCount - 1); | ||
| await Task.Delay(1000); | ||
| // Now back to the top | ||
| collectionView.ScrollTo(0); | ||
| await Task.Delay(1000); | ||
| if (handler.Controller is CacheTestItemsViewController controller | ||
| && controller.DelegateFlowLayout is CacheMissCountingDelegate cacheMissCounter) | ||
| { | ||
| // Different screen sizes and timings mean this isn't 100% predictable. But we can work out some conditions | ||
| // which will tell us that the cache is completely broken and test for those. | ||
| // With 15 items in the list, we can assume a minimum of 15 size cache misses until the cache is populated. | ||
| // Plus at least one for the initial proxy item measurement. | ||
| // The bugs we are trying to avoid clear the cache prematurely and cause _every_ GetSizeForItem call | ||
| // to miss the cache, so scrolling top to bottom and back with 15 items we would see at _least_ 30 | ||
| // cache misses, likely more (since item sizes will be retrieved more than once as items scroll). | ||
| // If we have fewer than 20 cache misses, we at least know that the cache isn't being wiped as we scroll. | ||
| int missCountThreshold = 20; | ||
| int actualMissCount = cacheMissCounter.CacheMissCount; | ||
| Assert.True(actualMissCount < missCountThreshold, $"Cache miss count {actualMissCount} was higher than the threshold value of {missCountThreshold}"); | ||
| } | ||
| else | ||
| { | ||
| // Something went wrong with this test | ||
| Assert.Fail("Wrong controller type in the test; is the handler registration broken?"); | ||
| } | ||
| }); | ||
| } | ||
| } | ||
| } |
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