統(tǒng)一彈登錄頁面，有的是在push出來的頁面彈登錄頁面,有的是在present頁面彈登錄頁面
說明 ：
例如：A present B A就是presenting view controller（彈出VC）； B就是presented view controller（被彈出VC）；

解決方案：

//登錄
- (void)presentLoginVC
{
    PhoneLoginViewController *loginVC = Storyboard(@"Main", @"PhoneLoginViewController");
    UINavigationController *loginNav = [[UINavigationController alloc] initWithRootViewController:loginVC];
    UIViewController *viewController = [UIApplication sharedApplication].keyWindow.rootViewController;
    /* viewController.presentedViewController只有present才有值，push的時候?yàn)閚il
     */

//防止重復(fù)彈
    if ([viewController.presentedViewController isKindOfClass:[UINavigationController class]]) {
        UINavigationController *navigation = (id)viewController.presentedViewController;
        if ([navigation.topViewController isKindOfClass:[PhoneLoginViewController class]]) {
            return;
        }
    }
    if (viewController.presentedViewController) {
        //要先dismiss結(jié)束后才能重新present否則會出現(xiàn)Warning: Attempt to present <UINavigationController: 0x7fdd22262800> on <UITabBarController: 0x7fdd21c33a60> whose view is not in the window hierarchy!就會present不出來登錄頁面
        [viewController.presentedViewController dismissViewControllerAnimated:false completion:^{
            [viewController presentViewController:loginNav animated:true completion:nil];
        }];
    }else {
        [viewController presentViewController:loginNav animated:true completion: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.
這個是自定義cell調(diào)用了基類的設(shè)置高度的方法，在tableview沒有實(shí)現(xiàn)- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath這個代理方法，然后就會出現(xiàn)這個警告。