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[iOS] Fabric: Fixes crash of dynamic color when light/dark mode changed #48496

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[iOS] Fabric: Fixes crash of dynamic color when light/dark mode changed #48496

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795e684
fix crash
zhongwuzw Nov 8, 2024
adeafa9
Merge commit 'b867c01fa624a3140ac1b8415b34b6db33fae1b4' into features…
zhongwuzw Jan 5, 2025
a720b3d
format
zhongwuzw Jan 5, 2025
8949170
pre-calculate the hash and store it as an associated object on the U…
zhongwuzw Jan 15, 2025
3e72b4d
update
zhongwuzw Jan 15, 2025
dad55b5
Apply review back
zhongwuzw Jan 21, 2025
fabf86f
Move category to HostPlatformColor
zhongwuzw Feb 3, 2025
6329f2e
Put hash value to constructor
zhongwuzw Feb 4, 2025
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5 changes: 4 additions & 1 deletion ...ctCommon/react/renderer/graphics/platform/ios/react/renderer/graphics/HostPlatformColor.h
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,8 @@ struct Color {
Color(const ColorComponents& components);
Color(std::shared_ptr<void> uiColor);
int32_t getColor() const;
int32_t getUIColorHash() const;

std::shared_ptr<void> getUIColor() const {
return uiColor_;
}
Expand All @@ -49,6 +51,7 @@ struct Color {

private:
std::shared_ptr<void> uiColor_;
mutable std::size_t uiColorHashValue_;
};

namespace HostPlatformColor {
Expand Down Expand Up @@ -104,7 +107,7 @@ template <>
struct std::hash<facebook::react::Color> {
size_t operator()(const facebook::react::Color& color) const {
auto seed = size_t{0};
facebook::react::hash_combine(seed, color.getColor());
facebook::react::hash_combine(seed, color.getUIColorHash());
return seed;
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@javache No value in calling hash_combine again with seed 0.

Suggested change
auto seed = size_t{0};
facebook::react::hash_combine(seed, color.getColor());
facebook::react::hash_combine(seed, color.getUIColorHash());
return seed;
return color.getUIColorHash();

}
};
46 changes: 43 additions & 3 deletions ...tCommon/react/renderer/graphics/platform/ios/react/renderer/graphics/HostPlatformColor.mm
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Expand Up @@ -73,18 +73,24 @@ int32_t ColorFromUIColor(UIColor *color)
((int)round((float)rgba[1] * ratio) & 0xff) << 8 | ((int)round((float)rgba[2] * ratio) & 0xff);
}

int32_t ColorFromUIColor(const std::shared_ptr<void> &uiColor)
int32_t ColorFromUIColorForSpecificTraitCollection(
const std::shared_ptr<void> &uiColor,
UITraitCollection *traitCollection)
{
UIColor *color = (UIColor *)unwrapManagedObject(uiColor);
if (color) {
UITraitCollection *currentTraitCollection = [UITraitCollection currentTraitCollection];
color = [color resolvedColorWithTraitCollection:currentTraitCollection];
color = [color resolvedColorWithTraitCollection:traitCollection];
return ColorFromUIColor(color);
}

return 0;
}

int32_t ColorFromUIColor(const std::shared_ptr<void> &uiColor)
{
return ColorFromUIColorForSpecificTraitCollection(uiColor, [UITraitCollection currentTraitCollection]);
}

UIColor *_Nullable UIColorFromComponentsColor(const facebook::react::ColorComponents &components)
{
if (components.colorSpace == ColorSpace::DisplayP3) {
Expand Down Expand Up @@ -142,6 +148,40 @@ int32_t ColorFromUIColor(const std::shared_ptr<void> &uiColor)
return static_cast<float>(rgba[channelId]);
}

int32_t Color::getUIColorHash() const
{
if (!uiColorHashValue_) {
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@javache javache Jan 14, 2025 •
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Would this work?

UIColor *color = (UIColor *)unwrapManagedObject(uiColor_);
return [color hashValue];

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@cipolleschi cipolleschi Jan 14, 2025 •
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The point here is: the UIColor does not change when the UITraitCollection changes.
It changes only when we resolve the uicolor against the trait collection.

The uiColor is the actual invariant here, we don't need to compute the hash resolving the uicolor against all the trait collections.

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@zhongwuzw zhongwuzw Jan 14, 2025 •
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@javache @cipolleschi I don't know details about how UIColor wether implements hash correctly. But seems the hash value is different even two dynamic colors have the same color in all trait collections.

For example: Two methods like below, [self dynamicColor].hash is not equal to [self dynamicColor1].hash. Actually they are the same color. So it may have potential issues if we use the hash value to check equality?

+ (UIColor *)dynamicColor {
  return [UIColor colorWithDynamicProvider:^UIColor * _Nonnull(UITraitCollection * _Nonnull traitCollection) {
    if (traitCollection.userInterfaceStyle == UIUserInterfaceStyleDark) {
      return [UIColor whiteColor];
    } else {
      return [UIColor blackColor];
    }
  }];
}

+ (UIColor *)dynamicColor1 {
  return [UIColor colorWithDynamicProvider:^UIColor * _Nonnull(UITraitCollection * _Nonnull traitCollection) {
    if (traitCollection.userInterfaceStyle == UIUserInterfaceStyleDark) {
      return [UIColor whiteColor]; 
    } else {
      return [UIColor blackColor]; 
    }
  }];
}

PS. The crash disappeared if we return color.hash.

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So UIColor hashValue is probably just falling back to NSObject, which means the value won't change over the objects lifetime, but also can't be reliably used to compare objects that are equal :(

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My concern is that hashing is supposed to be cheap, and we use it implicitly in a number of different places. This makes the common case of a non-platform color significantly more expensive.

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The hash is computed only once, when needed the first time, and then cached in the uiColorHashValue_. Isn't that enough? The tradeoff is that we recompute the same hash if we have two instances of the same color, but that should be ok, no?

return uiColorHashValue_;
}

static UITraitCollection *darkModeTraitCollection =
[UITraitCollection traitCollectionWithUserInterfaceStyle:UIUserInterfaceStyleDark];
auto darkColor = ColorFromUIColorForSpecificTraitCollection(uiColor_, darkModeTraitCollection);

static UITraitCollection *lightModeTraitCollection =
[UITraitCollection traitCollectionWithUserInterfaceStyle:UIUserInterfaceStyleLight];
auto lightColor = ColorFromUIColorForSpecificTraitCollection(uiColor_, lightModeTraitCollection);

static UITraitCollection *darkModeAccessibilityContrastTraitCollection =
[UITraitCollection traitCollectionWithTraitsFromCollections:@[
darkModeTraitCollection,
[UITraitCollection traitCollectionWithAccessibilityContrast:UIAccessibilityContrastHigh]
]];
auto darkAccessibilityContrastColor =
ColorFromUIColorForSpecificTraitCollection(uiColor_, darkModeAccessibilityContrastTraitCollection);

static UITraitCollection *lightModeAccessibilityContrastTraitCollection =
[UITraitCollection traitCollectionWithTraitsFromCollections:@[
lightModeTraitCollection,
[UITraitCollection traitCollectionWithAccessibilityContrast:UIAccessibilityContrastHigh]
]];
auto lightAccessibilityContrastColor =
ColorFromUIColorForSpecificTraitCollection(uiColor_, lightModeAccessibilityContrastTraitCollection);
uiColorHashValue_ = facebook::react::hash_combine(
darkColor, lightColor, darkAccessibilityContrastColor, lightAccessibilityContrastColor);
return uiColorHashValue_;
}

} // namespace facebook::react

NS_ASSUME_NONNULL_END
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