导航头像放大缩小动画简单实现

效果图.gif

#import "ViewController.h"

@interface ViewController ()
{
    
}

@property (nonatomic , strong) UIImageView *headerImageView;     /**< <#description#> */

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    UIView *titleView = [[UIView alloc] init];
    self.navigationItem.titleView = titleView;
    
    NSLog(@"%@",NSStringFromCGRect(self.navigationItem.titleView.frame));
    
    self.headerImageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 40, 40)];
    self.headerImageView.layer.cornerRadius = 20.f;
    self.headerImageView.layer.masksToBounds = YES;
    self.headerImageView.image = [UIImage imageNamed:@"head"];
  
    // 保证用户头像水平居中
    self.headerImageView.center = CGPointMake(titleView.center.x, 0);
    [titleView addSubview:self.headerImageView];
    
    
    UITableView *tableView = [[UITableView alloc] initWithFrame:CGRectMake(0, 0, [UIScreen mainScreen].bounds.size.width, [UIScreen mainScreen].bounds.size.height)];
    tableView.backgroundColor = [UIColor whiteColor];
    [self.view addSubview:tableView];
    
    tableView.delegate = self;
}



- (void)scrollViewDidScroll:(UIScrollView *)scrollView {

    CGFloat offsetY = scrollView.contentOffset.y + scrollView.contentInset.top;
    CGFloat scale = 1.f;
    
    // 放大
    if (offsetY < 0) {
        scale = MIN(1.5, 1 - offsetY / 300);
    } else if (offsetY > 0) {
        // 缩小
        scale = MAX(0.45, 1 - offsetY / 300);
    }
    
    //进行缩放
    self.headerImageView.transform = CGAffineTransformMakeScale(scale, scale);
    // 保证缩放后y坐标不变
    CGRect frame = self.headerImageView.frame;
    frame.origin.y = -self.headerImageView.layer.cornerRadius / 2;
    self.headerImageView.frame = frame;
}


@end