UIScrollView的折叠效果

#import "ViewController.h"
#import <Masonry/Masonry.h>

@interface ViewController ()

@property (nonatomic, strong) UIScrollView *scrollView;
@property (nonatomic, strong) NSMutableArray *dataArrayM;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    [self.view addSubview:self.scrollView];
    [self createLabels];
}

- (void)createLabels {
    UILabel *lastLabel = nil;
    for (NSInteger i = 0; i < 10; i++) {
        UILabel *label = [[UILabel alloc] init];
        label.numberOfLines = 0;
        label.layer.borderColor = [UIColor greenColor].CGColor;
        label.layer.borderWidth = 2.0;
        label.text = [self randomText];
        label.userInteractionEnabled = YES;
        UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(onTap:)];
        [label addGestureRecognizer:tap];
        label.textAlignment = NSTextAlignmentLeft;
        label.textColor = [self randomColor];
        [self.scrollView addSubview:label];
        [label mas_makeConstraints:^(MASConstraintMaker *make) {
            make.left.mas_equalTo(15);
            make.right.mas_equalTo(self.view.mas_right).mas_offset(-15);
            make.height.mas_equalTo(40);
            if (lastLabel) {
                make.top.mas_equalTo(lastLabel.mas_bottom).mas_offset(20);
            } else {
                make.top.mas_equalTo(self.scrollView.mas_top).mas_offset(20);
            }
        }];
        lastLabel = label;
        [self.dataArrayM addObject:[@[label, @(NO)] mutableCopy]];
    }
    [self.scrollView mas_makeConstraints:^(MASConstraintMaker *make) {
        make.edges.mas_equalTo(self.view);
        make.bottom.mas_equalTo(lastLabel.mas_bottom).mas_offset(20);// 让scrollview的contentSize随着内容的增多而变化
    }];
}

- (UIScrollView *)scrollView {
    if (!_scrollView) {
        _scrollView = [[UIScrollView alloc] init];
        _scrollView.pagingEnabled = NO;
        _scrollView.backgroundColor = [UIColor lightGrayColor];
    }
    return _scrollView;
}

- (void)onTap:(UITapGestureRecognizer *)sender {
    UIView *tapView = sender.view;//获取到点击的Label
    NSUInteger index = 0;
    for (NSMutableArray *array in self.dataArrayM) {
        UILabel *view = [array firstObject];
        if (view == tapView) {
            NSNumber *state = [array lastObject];
            if ([state boolValue] == YES) {// 当前是展开状态的话，就收缩
                [view mas_updateConstraints:^(MASConstraintMaker *make) {
                    make.height.mas_equalTo(40);
                }];
            } else {
                UIView *preView = nil;
                UIView *nextView = nil;
                if (index - 1 < self.dataArrayM.count && index >= 1) {
                    preView = [[self.dataArrayM objectAtIndex:index - 1] firstObject];
                }
                if (index + 1 < self.dataArrayM.count) {
                    nextView = [[self.dataArrayM objectAtIndex:index + 1] firstObject];
                }
                [view mas_remakeConstraints:^(MASConstraintMaker *make) {
                    make.left.mas_equalTo(15);
                    make.right.mas_equalTo(self.view.mas_right).mas_offset(-15);
                    if (preView) {
                        make.top.mas_equalTo(preView.mas_bottom).mas_offset(20);
                    } else {
                        make.top.mas_equalTo(20);
                    }
                }];
                if (nextView) {
                    [nextView mas_updateConstraints:^(MASConstraintMaker *make) {
                        make.top.mas_equalTo(view.mas_bottom).mas_offset(20);
                    }];
                }
            }
            [array replaceObjectAtIndex:1 withObject:@(!state.boolValue)];
            [UIView animateWithDuration:0.35 animations:^{
                [self.view layoutIfNeeded];
            } completion:^(BOOL finished) {
            }];
            break;
        }
        index++;
    }
}

- (NSMutableArray *)dataArrayM {
    if (!_dataArrayM) {
        _dataArrayM = [NSMutableArray array];
    }
    return _dataArrayM;
}

- (UIColor *)randomColor {
    CGFloat hue = (arc4random() % 256 / 256.0);
    CGFloat saturation = (arc4random() % 128 / 256.0) + 0.5;
    CGFloat brightness = (arc4random() % 128 / 256.0) + 0.5;
    return [UIColor colorWithHue:hue saturation:saturation brightness:brightness alpha:1];
}

- (NSString *)randomText {
    CGFloat count = arc4random() % 50 + 5;
    NSMutableString *str = [[NSMutableString alloc] init];
    for (NSInteger i = 0; i < count; i++) {
        [str appendString:@"测试数据很长，"];
    }
    return str;
}

@end