When adding/removing/reloading cells in a UICollectionView using the FlowLayout the cells fade in/out. When doing things like updating a progress bar you get a lot of annoying flashing because of this, this category will prevent that. As an added benefit rotation animations will now show the cells moving into position.

UICollectionViewFlowLayout+NoFade.m

//
//  UICollectionViewFlowLayout+NoFade.m
//
//  Created by Rob Booth on 3/4/14.

#import "UICollectionViewFlowLayout+NoFade.h"
#import <objc/runtime.h>

@implementation UICollectionViewFlowLayout (NoFade)

+ (void) load
{
	Method original, swizzled;

	original = class_getInstanceMethod(self, @selector(initialLayoutAttributesForAppearingItemAtIndexPath:));
	swizzled = class_getInstanceMethod(self, @selector(noFadeInitialLayoutAttributesForAppearingItemAtIndexPath:));

	method_exchangeImplementations(original, swizzled);

	original = class_getInstanceMethod(self, @selector(finalLayoutAttributesForDisappearingItemAtIndexPath:));
	swizzled = class_getInstanceMethod(self, @selector(noFadeFinalLayoutAttributesForDisappearingItemAtIndexPath:));

	method_exchangeImplementations(original, swizzled);
}

- (UICollectionViewLayoutAttributes *)noFadeInitialLayoutAttributesForAppearingItemAtIndexPath:(NSIndexPath *)itemIndexPath
{
	// Not recursive, due to method exhange in load above
	// This is because we can't call super in a catagory
	UICollectionViewLayoutAttributes * attributes = [self noFadeInitialLayoutAttributesForAppearingItemAtIndexPath:itemIndexPath];

	attributes.alpha = 1.0;

	return attributes;
}

- (UICollectionViewLayoutAttributes *)noFadeFinalLayoutAttributesForDisappearingItemAtIndexPath:(NSIndexPath *)itemIndexPath
{
	// Not recursive, due to method exhange in load above
	// This is because we can't call super in a catagory
	UICollectionViewLayoutAttributes * attributes = [self noFadeFinalLayoutAttributesForDisappearingItemAtIndexPath:itemIndexPath];

	attributes.alpha = 1.0;

	return attributes;
}

@end

Thanks so much for this.
I had this fading problem when animating the constraints on the CollectionView. The animation is way nicer now too. Good work!

Hi,
The header of collectionView is still blinking by using this category. Anyway to fix that ?

now app crashed if I try to show UIActivityViewContoller like this:

UIActivityViewController *activityViewController =
[[UIActivityViewController alloc] initWithActivityItems:@["text",[UIImage imageNamed:@"some image"]]
applicationActivities:nil];

platform:
xCode 7.2 (7C68) iOS 9.2 iphone 5 simulator
Do you have any suggestions how to fix this?

Any idea how to do this in Swift? Overriding load isn't an option anymore, and swapping the methods in initialize will not prevent the recursive call.

The modern way to do this would be subclassing the flow layout, like so:

import UIKit

class NoFadeFlowLayout: UICollectionViewFlowLayout {
    
    override func initialLayoutAttributesForAppearingItem(at itemIndexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        let attrs = super.initialLayoutAttributesForAppearingItem(at: itemIndexPath)
        attrs?.alpha = 1.0
        return attrs
    }
    
    override func finalLayoutAttributesForDisappearingItem(at itemIndexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        let attrs = super.finalLayoutAttributesForDisappearingItem(at: itemIndexPath)
        attrs?.alpha = 1.0
        return attrs
    }
    
}

Thank you, @tooolbox!