我需要执行一个动作(清空一个数组)，当UINavigationController的后退按钮被按下，而按钮仍然导致堆栈上的前一个ViewController出现。我如何使用swift来实现这一点?
当前回答
这就是我的解
extension UINavigationController: UINavigationBarDelegate {
public func navigationBar(_ navigationBar: UINavigationBar, shouldPop item: UINavigationItem) -> Bool {
if let shouldBlock = self.topViewController?.shouldPopFromNavigation() {
return shouldBlock
}
return true
}
}
extension UIViewController {
@objc func shouldPopFromNavigation() -> Bool {
return true
}
}
在你的视图控制器中，你可以这样处理:
@objc override func shouldPopFromNavigation() -> Bool {
// Your dialog, example UIAlertViewController or whatever you want
return false
}
其他回答
在我的例子中，viewWillDisappear效果最好。但在某些情况下，必须修改之前的视图控制器。所以这是我的解决方案访问之前的视图控制器，它在Swift 4中工作:
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
if isMovingFromParentViewController {
if let viewControllers = self.navigationController?.viewControllers {
if (viewControllers.count >= 1) {
let previousViewController = viewControllers[viewControllers.count-1] as! NameOfDestinationViewController
// whatever you want to do
previousViewController.callOrModifySomething()
}
}
}
}
这就是我的解
extension UINavigationController: UINavigationBarDelegate {
public func navigationBar(_ navigationBar: UINavigationBar, shouldPop item: UINavigationItem) -> Bool {
if let shouldBlock = self.topViewController?.shouldPopFromNavigation() {
return shouldBlock
}
return true
}
}
extension UIViewController {
@objc func shouldPopFromNavigation() -> Bool {
return true
}
}
在你的视图控制器中，你可以这样处理:
@objc override func shouldPopFromNavigation() -> Bool {
// Your dialog, example UIAlertViewController or whatever you want
return false
}
只需control +拖动栏项到func下面。魅力工作
@IBAction func done(sender: AnyObject) {
if((self.presentingViewController) != nil){
self.dismiss(animated: false, completion: nil)
print("done")
}
}
如果你正在使用navigationController，那么将UINavigationControllerDelegate协议添加到类中，并添加delegate方法，如下所示:
class ViewController:UINavigationControllerDelegate {
func navigationController(navigationController: UINavigationController, willShowViewController viewController: UIViewController,
animated: Bool) {
if viewController === self {
// do here what you want
}
}
}
每当导航控制器滑到新屏幕时，就调用此方法。如果返回按钮被按下，新的视图控制器就是ViewController本身。
override func willMove(toParent parent: UIViewController?)
{
super.willMove(toParent: parent)
if parent == nil
{
print("This VC is 'will' be popped. i.e. the back button was pressed.")
}
}
