// 初始化控制器,SecondViewController类继承自UIViewController

 　SecondViewController *vc = [[SecondViewController alloc] init];

    // 把vc包装成UIPopoverController

    UIPopoverController *popover = [[UIPopoverController alloc] initWithContentViewController:vc];

　 // 设置popover的指向,

　 // 指向当前控制上button按钮,所以FromRect后跟bounds

　 // 如果是指向当前控制的View,则FromRect后跟frame

    [popover presentPopoverFromRect:self.button.bounds inView:self.button permittedArrowDirections:UIPopoverArrowDirectionAny animated:YES];

// 初始化控制器

    SecondViewController *vc = [[SecondViewController alloc] init];

    // modal出来是个popover

    vc.modalPresentationStyle = UIModalPresentationPopover;

    // 取出vc所在的UIPopoverPresentationController

    vc.popoverPresentationController.sourceView = self.button;

    vc.popoverPresentationController.sourceRect = self.button.bounds;

    [self presentViewController:vc animated:YES completion:nil];