在 tableView 上设置 refreshControl

UIRefreshControl *refreshControl = [[UIRefreshControl alloc] init];
[refreshControl addTarget:self action:@selector(pullToRefresh:) forControlEvents:UIControlEventValueChanged];
self.scrollView.alwaysBounceVertical = YES;
[self.scrollView addSubview:refreshControl];

- (void)pullToRefresh:(UIRefreshControl*) sender{
//Do work off the main thread
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    // Simulate network traffic (sleep for 2 seconds)
    [NSThread sleepForTimeInterval:2];
    //Update data
    //Call complete on the main thread
    dispatch_sync(dispatch_get_main_queue(), ^{
        //Update network activity UI
        NSLog(@"COMPLETE");
        [sender endRefreshing];
    });
});

}