How to clear font cache filled with emoji characters?

Question

I am developing keyboard extension for iPhone. There is an emoji screen smilar to Apples own emoji keyboard that shows some 800 emoji characters in UICollectionView

Answer 1

In my case, the plain CATextLayer helped to reduce the memory usage of my app. When I used the UILabel to render Emojis the keyboard extension memory was increasing from ~16MB to ~76MB. After the replacement of the UILabel with the CATextLayer, the keyboard extension memory increasing from ~16MB to only ~26MB.

Previous UICollectionViewCell subclass setup:

- (instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];

    // somewhere in the header file 
    // @property (nonatomic, strong, readonly) UILabel *textLabel;
    _textLabel = [UILabel new];
    self.textLabel.font = [UIFont fontWithName:@"HelveticaNeue" size:28];
    self.textLabel.textAlignment = NSTextAlignmentCenter;
    [self addSubview:self.textLabel];
    // some auto layout logic using Masonry
    [self.textLabel mas_makeConstraints:^(MASConstraintMaker *make) {
        make.size.equalTo(self);
        make.center.equalTo(self);
    }];

    return self;
}

My UICollectionViewCell subclass setup with the CATextLayer:

- (instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];

    // somewhere in the header file 
    // @property (nonatomic, strong, readonly) CATextLayer *textLayer;
    _textLayer = [CATextLayer new];
    self.textLayer.frame = CGRectMake(0, 0, 33, 33);
    self.textLayer.font = CFBridgingRetain([UIFont fontWithName:@"HelveticaNeue" size:28].fontName);
    self.textLayer.fontSize = 28;
    self.textLayer.alignmentMode = kCAAlignmentCenter;
    [self.layer addSublayer:self.textLayer];

    return self;
}

Update

Sorry guys forgot to add the self.textLayer.contentsScale = [[UIScreen mainScreen] scale]; to get clear text. That unfortunately increased usage of memory from ~16MB to ~44MB, but still better than the UILabel solution.

Final UICollectionViewCell subclass setup with the CATextLayer:

- (instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];

    [self.layer setRasterizationScale:[[UIScreen mainScreen] scale]];

    // somewhere in the header file 
    // @property (nonatomic, strong, readonly) CATextLayer *textLayer;
    _textLayer = [CATextLayer new];
    self.textLayer.frame = CGRectMake(0, 0, 33, 33);
    self.textLayer.font = CFBridgingRetain([UIFont fontWithName:@"HelveticaNeue" size:28].fontName);
    self.textLayer.fontSize = 28;
    self.textLayer.alignmentMode = kCAAlignmentCenter;
    NSDictionary *newActions = @{
        @"onOrderIn": [NSNull null],
        @"onOrderOut": [NSNull null],
        @"sublayers": [NSNull null],
        @"contents": [NSNull null],
        @"bounds": [NSNull null]
    };
    self.textLayer.actions = newActions;
    [self.layer addSublayer:self.textLayer];

    [self.layer setShouldRasterize:YES];

    return self;
}