//1. 创建popVC

UIViewController*contentVC = [[UIViewControlleralloc]init];

contentVC.view.backgroundColor= [UIColorredColor];

//2. 设置popVC的尺寸

contentVC.preferredContentSize=CGSizeMake(300,300);

//3. 设置popVC为popOver

contentVC.modalPresentationStyle=UIModalPresentationPopover;

//4. 设置箭头方向

contentVC.popoverPresentationController.permittedArrowDirections=UIPopoverArrowDirectionUp;

//5. 设置参考系

contentVC.popoverPresentationController.sourceView=self.view;

//6. 设置箭头指向的对象

contentVC.popoverPresentationController.sourceRect=self.btn.frame;

//7. 展现popVC

[selfpresentViewController:contentVCanimated:YEScompletion:NULL];