autolayout under navigation bar

UIView *topLayoutGuide = self.topLayoutGuide;

NSDictionary *viewsDictionary = NSDictionaryOfVariableBindings(selectBuuton, itemTableView, itemCollection, topLayoutGuide);

constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|[topLayoutGuide]-[selectBuuton]-[itemTableView]"

                                                          options:0

                                                          metrics:nil

                                                            views:viewsDictionary];

    [self.view addConstraints:constraints];

這樣就能夠用VFL去實現view們顯示在navigationbar的下側了。

這裏能夠將topLayoutGuide當作一個UIView，在ios7中，就是讓他與其餘view平等了