简单的UIScrollView 下拉刷新

#import "ViewController.h"
@interface ViewController ()<UIScrollViewDelegate>{
    UIView * _loadView;
}

- (void)viewDidLoad {
    _loadView = [[UIView alloc] initWithFrame:CGRectMake(0,  -44, 320, 44)];
    //...
}

#pragam mark UIScrollView Delegate
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    _loadView.frame = CGRectMake(0, -44 - scrollView.contentOffset.y, 320, 44);
    if (scrollView.contentOffset.y<= -44) {
        //处理松开刷新提示
    }  else {
        //关闭松开刷新提示
    }
}

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
    if (scrollView.contentOffset.y<= -44) {
        //此处动画纯粹为了过度平滑
        [UIView animateWithDuration:0.2 animations:^(void) {
             scrollView.contentInset = UIEdgeInsetsMake(44, 0, 0, 0);
         }completion:^(BOOL complete) {
             //处理需要加载的东西
        }];
    }
}

//...