Pull-to-refresh
How to use
pod 'ELRefresh', '~> 0.0.1'
In your viewController's viewWillAppear function:
(onceToken should be a property of you viewController);

    dispatch_once(&_onceToken, ^{
        self.refreshView = [[ELRefreshView alloc] initWithScrollView:self.tableView refreshDirection:ELRefreshUpper];

        __weak ELViewController *weakSelf = self;
        self.refreshView.refreshBlock = ^{
            [weakSelf doString];
        };
    });

TO DO
Now just support RefreshView in the top.