参数标签＆＃39;（_：，viewControllerAfterViewController：）＆＃39;不匹配任何可用的重载

Question

此刻学习swift，任何帮助都会受到赞赏 - 将代码从swift 3更新为swift 4 - 在构建时出现以下错误：

  

参数标签＆＃39;（_：，viewControllerAfterViewController：）＆＃39;不匹配任何可用的重载

我认为与此错误相关的代码位于以下goToNextVC函数中：

<?php
    include 'db.php';
    $sql = $db->query("SELECT * FROM employee");
    $res = mysqli_fetch_assoc($sql);
    echo 'name:"'.$res['name'].'", salary: "'.$res['salary'].'"';
?>

完整代码：

     func goToNextVC() {
     let nextVC = pageViewController(self, viewControllerAfterViewController: viewControllers![0] )!
    setViewControllers([nextVC], direction: .Forward, animated: true, completion: nil)
}



    extension ViewController: UIPageViewControllerDataSource {

func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {

    // navigate right
    switch viewController {
    case cardsVC:
        return profileVC
    case profileVC:
        return nil
    case matchesVC:
        return cardsVC
    default:
        return nil
    }
}

}

Answer 1

此：

let nextVC = pageViewController(self, viewControllerAfterViewController: viewControllers![0] )!

需要：

let nextVC = pageViewController(self, viewControllerAfter: viewControllers![0] )!

当你在它时，你需要摆脱强制解包（!）。 pageViewController(_:viewControllerAfter:)可以返回nil，使用!会导致您的应用崩溃。

func goToNextVC() {
    if let viewControllers = viewControllers {
        if let nextVC = pageViewController(self, viewControllerAfter: viewControllers[0]) {
            setViewControllers([nextVC], direction: .Forward, animated: true, completion: nil)
        }
    }
}