Attempt to present <UINavigat

统一弹登录页面，有的是在push出来的页面弹登录页面,有的是在present页面弹登录页面

说明 ：

例如：A present B

A就是presenting view controller（弹出VC）；

B就是presented view controller（被弹出VC）；

解决方案：

//登录- (void)presentLoginVC{  

PhoneLoginViewController *loginVC = Storyboard(@"Main",@"PhoneLoginViewController");UINavigationController*loginNav = [[UINavigationControlleralloc] initWithRootViewController:loginVC];UIViewController*viewController = [UIApplicationsharedApplication].keyWindow.rootViewController;/* viewController.presentedViewController只有present才有值，push的时候为nil

*///防止重复弹

if([viewController.presentedViewControllerisKindOfClass:[UINavigationControllerclass]]) {

UINavigationController*navigation = (id)viewController.presentedViewController;if([navigation.topViewControllerisKindOfClass:[PhoneLoginViewController class]]) {return;        }    }

if(viewController.presentedViewController) {//要先dismiss结束后才能重新present否则会出现Warning: Attempt to present on whose view is not in the window hierarchy!就会present不出来登录页面[viewController.presentedViewControllerdismissViewControllerAnimated:falsecompletion:^{            [viewController presentViewController:loginNav animated:truecompletion:nil];        }];    }else{        [viewController presentViewController:loginNav animated:truecompletion:nil];    }}

2.Warning once only: Detected a case where constraints ambiguously suggest a height of zero for a tableview cell's content view. We're considering the collapse unintentional and using standard height instead.

这个是自定义cell调用了基类的设置高度的方法，在tableview没有实现- (CGFloat)tableView:(UITableView)tableView heightForRowAtIndexPath:(NSIndexPath)indexPath这个代理方法，然后就会出现这个警告。