iOS 11 下 UICollectionView 的Heade

这个问题在之前的 iOS 10 上是没有的，iOS 11 新出之后才出现。在使用了- collectionView: viewForSupplementaryElementOfKind: atIndexPath:的 UICollectionView 页面中，滑动页面的时候滚动条会被 HeaderView 遮挡.

修改前的样子:

//
//  CustomCollectionReusableView.m
//  EMall
//
//  Created by YJHou on 2017/9/16.
//  Copyright © 2017年 stackhou . All rights reserved.
//

#import "CustomCollectionReusableView.h"

@interface CustomCollectionReusableView ()

@property (nonatomic, strong) UILabel *showLabel; /**< 显示控件 */

@end

@implementation CustomCollectionReusableView

- (void)layoutSubviews {
    [super layoutSubviews];
    [self _setUpSubViews];
}

- (void)_setUpSubViews {
    [self addSubview:self.showLabel];
}

#pragma mark - Lazy
- (UILabel *)showLabel{    
    if (!_showLabel) {
        _showLabel = [[UILabel alloc] initWithFrame:CGRectMake(20, 20, 120, self.frame.size.height)];
        _showLabel.font = [UIFont systemFontOfSize:13];
        _showLabel.textAlignment = NSTextAlignmentLeft;
        _showLabel.backgroundColor = [UIColor clearColor];
        _showLabel.textColor = [UIColor redColor];
    }
    return _showLabel;
}

@end

修复完成后

//
//  CustomCollectionReusableView.m
//  EMall
//
//  Created by YJHou on 2017/9/16.
//  Copyright © 2017年 stackhou . All rights reserved.
//

#import "CustomCollectionReusableView.h"

#ifdef __IPHONE_11_0
@interface CustomLayer : CALayer

@end
#endif

@interface CustomCollectionReusableView ()

@property (nonatomic, strong) UILabel *showLabel; /**< 显示控件 */

@end

#ifdef __IPHONE_11_0
@implementation CustomLayer

- (CGFloat) zPosition {
    return 0;
}

@end
#endif

@implementation CustomCollectionReusableView

- (void)layoutSubviews {
    [super layoutSubviews];
    [self _setUpSubViews];
}

- (void)_setUpSubViews {
    [self addSubview:self.showLabel];
}

#pragma mark - Lazy
- (UILabel *)showLabel{    
    if (!_showLabel) {
        _showLabel = [[UILabel alloc] initWithFrame:CGRectMake(20, 20, 120, self.frame.size.height)];
        _showLabel.font = [UIFont systemFontOfSize:13];
        _showLabel.textAlignment = NSTextAlignmentLeft;
        _showLabel.backgroundColor = [UIColor clearColor];
        _showLabel.textColor = [UIColor redColor];
    }
    return _showLabel;
}

#ifdef __IPHONE_11_0
+ (Class)layerClass {
    return [CustomLayer class];
}
#endif

@end