自定义刷新控件的实现原理

- (void)viewDidLoad {
[super viewDidLoad];

UIButton *button  = [UIButton buttonWithType:UIButtonTypeCustom];
button.frame = CGRectMake(0, -30, self.view.bounds.size.width, 30);
[button setTitle:@"下拉刷新" forState:UIControlStateNormal];
[self.view addSubview:button];
button.backgroundColor = [UIColor redColor];
self.refreshButton = button;
[self.tableView addSubview:button];

}

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

NSLog(@"%f",scrollView.contentOffset.y);

if (scrollView.contentInset.top == 30)
return;

if (scrollView.contentOffset.y <= -30) {

[self.refreshButton setTitle:@"松开刷新" forState:UIControlStateNormal];

}
else{
[self.refreshButton setTitle:@"下拉刷新" forState:UIControlStateNormal];
}
}

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate{
if (scrollView.contentOffset.y <= -30) {

[UIView animateWithDuration:0.5 animations:^{
[self.refreshButton setTitle:@"正在刷新" forState:UIControlStateNormal];
scrollView.contentInset = UIEdgeInsetsMake(30, 0, 0, 0);
}];
}

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
[UIView animateWithDuration:0.5 animations:^{

scrollView.contentInset = UIEdgeInsetsMake(0, 0, 0, 0);
}];

});

}