ios - 如何导航回已删除的 PageViewController 条目/更改 PageViewController 条目

Question

情况:我想从数据条目列表导航回我的 PageViewController。

before 和 previous 函数起作用

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


    if ((viewController as! LocationViewController).mLocationIndex > 0){
        let storyboard = UIStoryboard(name: "Main", bundle: nil)
        let vc = storyboard.instantiateViewControllerWithIdentifier("LocationViewController") as! LocationViewController
        vc.mLocationIndex = (viewController as! LocationViewController).mLocationIndex - 1
        return vc
    }
    return nil
}

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

    let locCount = DataManager.sharedInstance.getLocationCount()
    if ((viewController as! LocationViewController).mLocationIndex < locCount - 1){
        let storyboard = UIStoryboard(name: "Main", bundle: nil)
        let vc = storyboard.instantiateViewControllerWithIdentifier("LocationViewController") as! LocationViewController
        vc.mLocationIndex = (viewController as! LocationViewController).mLocationIndex + 1
        return vc
    }

    return nil
}

问题: 如果我在 viewDidLoad() 中设置 UIPageViewController 的 UIViewController(Location)，我可以通过 UIPageViewController 到我的 UITableView 并且我能够导航回来并且一切正常。但是我想删除我的 UITableView 中的位置，当我删除我想返回的位置时(每个位置后面都是 CoreData 中的 dada)它崩溃了，因为数据在 CoreData 中消失了。

我尝试在 viewWillAppear(animated: Bool) 中设置 UIViewController(Location)。现在我可以删除条目，向后导航并拥有自己的设置 UIViewController(Location) BUT - 如果我滚动到上一个 View 的“副本”尽管 viewControllerBeforeViewController 返回 nil 只是显示...这怎么可能？

第一个 viewDidLoad() 版本的代码片段:

class MainPageViewController: UIPageViewController {

override func viewDidLoad() {
    super.viewDidLoad()
    dataSource = self

    let dM = DataManager.sharedInstance
    let storyboard = UIStoryboard(name: "Main", bundle: nil)
    let vc = storyboard.instantiateViewControllerWithIdentifier("LocationViewController") as! LocationViewController
    dM.mActualLocationIndex = 0

    // check if the index is too big (deleted data)
    if (dM.mActualLocationIndex < dM.getLocationCount()){
        vc.mLocationIndex = dM.mActualLocationIndex
    } else {
        vc.mLocationIndex = 0
        dM.mActualLocationIndex = 0
    }
    vc.mLocationIndex = 0
    setViewControllers([vc], direction: UIPageViewControllerNavigationDirection.Forward, animated: true, completion: nil)

}

override func viewWillAppear(animated: Bool) {

}

Answer 1

我找到了一个解决方案:

extension UIPageViewController {
    func setViewControllerAndClearCache(vc: UIViewController){
        setViewControllers([vc], direction: .Forward, animated: true, completion: { _ in
            dispatch_async(dispatch_get_main_queue(), {
                self.setViewControllers([vc], direction: .Forward, animated: false, completion: nil)                
            })
        })
    }
}

使用 setViewControllerAndClearCache(vc: UIViewController)，我在 UIPageViewController 的 viewWillAppear() 中调用，我能够“清除现金 View ”，当我返回时，不再有前一个 View 的“副本”!