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
在Swift 5和Xcode 10.2中
请不要添加自定义栏按钮项，使用默认行为。
不需要viewWillDisappear，不需要自定义BarButtonItem等…
最好是检测VC何时从其父对象中移除。
使用这两个函数中的任意一个
override func willMove(toParent parent: UIViewController?) {
super.willMove(toParent: parent)
if parent == nil {
callStatusDelegate?.backButtonClicked()//Here write your code
}
}
override func didMove(toParent parent: UIViewController?) {
super.didMove(toParent: parent)
if parent == nil {
callStatusDelegate?.backButtonClicked()//Here write your code
}
}
如果你想停止返回按钮的默认行为，然后添加自定义BarButtonItem。
其他回答
一种选择是实现您自己的自定义后退按钮。你需要添加以下代码到你的viewDidLoad方法:
- (void) viewDidLoad {
[super viewDidLoad];
self.navigationItem.hidesBackButton = YES;
UIBarButtonItem *newBackButton = [[UIBarButtonItem alloc] initWithTitle:@"Back" style:UIBarButtonItemStyleBordered target:self action:@selector(back:)];
self.navigationItem.leftBarButtonItem = newBackButton;
}
- (void) back:(UIBarButtonItem *)sender {
// Perform your custom actions
// ...
// Go back to the previous ViewController
[self.navigationController popViewControllerAnimated:YES];
}
更新:
以下是Swift的版本:
override func viewDidLoad {
super.viewDidLoad()
self.navigationItem.hidesBackButton = true
let newBackButton = UIBarButtonItem(title: "Back", style: UIBarButtonItemStyle.Bordered, target: self, action: "back:")
self.navigationItem.leftBarButtonItem = newBackButton
}
@objc func back(sender: UIBarButtonItem) {
// Perform your custom actions
// ...
// Go back to the previous ViewController
self.navigationController?.popViewControllerAnimated(true)
}
更新2:
以下是Swift 3的版本:
override func viewDidLoad {
super.viewDidLoad()
self.navigationItem.hidesBackButton = true
let newBackButton = UIBarButtonItem(title: "Back", style: UIBarButtonItemStyle.plain, target: self, action: #selector(YourViewController.back(sender:)))
self.navigationItem.leftBarButtonItem = newBackButton
}
@objc func back(sender: UIBarButtonItem) {
// Perform your custom actions
// ...
// Go back to the previous ViewController
_ = navigationController?.popViewController(animated: true)
}
Swift 5 __ Xcode 11.5
在我的情况下，我想做一个动画，当它完成后，返回。 一种覆盖后退按钮默认动作的方法 调用你的自定义动作是这样的:
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
setBtnBack()
}
private func setBtnBack() {
for vw in navigationController?.navigationBar.subviews ?? [] where "\(vw.classForCoder)" == "_UINavigationBarContentView" {
print("\(vw.classForCoder)")
for subVw in vw.subviews where "\(subVw.classForCoder)" == "_UIButtonBarButton" {
let ctrl = subVw as! UIControl
ctrl.removeTarget(ctrl.allTargets.first, action: nil, for: .allEvents)
ctrl.addTarget(self, action: #selector(backBarBtnAction), for: .touchUpInside)
}
}
}
@objc func backBarBtnAction() {
doSomethingBeforeBack { [weak self](isEndedOk) in
if isEndedOk {
self?.navigationController?.popViewController(animated: true)
}
}
}
private func doSomethingBeforeBack(completion: @escaping (_ isEndedOk:Bool)->Void ) {
UIView.animate(withDuration: 0.25, animations: { [weak self] in
self?.vwTxt.alpha = 0
}) { (isEnded) in
completion(isEnded)
}
}
或者你可以使用这个方法一次来探索NavigationBar视图层次结构，并获得访问_UIButtonBarButton视图的索引，转换为UIControl，删除目标-动作，并添加你的自定义目标-动作:
private func debug_printSubviews(arrSubviews:[UIView]?, level:Int) {
for (i,subVw) in (arrSubviews ?? []).enumerated() {
var str = ""
for _ in 0...level {
str += "\t"
}
str += String(format: "%2d %@",i, "\(subVw.classForCoder)")
print(str)
debug_printSubviews(arrSubviews: subVw.subviews, level: level + 1)
}
}
// Set directly the indexs
private func setBtnBack_method2() {
// Remove or comment the print lines
debug_printSubviews(arrSubviews: navigationController?.navigationBar.subviews, level: 0)
let ctrl = navigationController?.navigationBar.subviews[1].subviews[0] as! UIControl
print("ctrl.allTargets: \(ctrl.allTargets)")
ctrl.removeTarget(ctrl.allTargets.first, action: nil, for: .allEvents)
print("ctrl.allTargets: \(ctrl.allTargets)")
ctrl.addTarget(self, action: #selector(backBarBtnAction), for: .touchUpInside)
print("ctrl.allTargets: \(ctrl.allTargets)")
}
在Swift 5和Xcode 10.2中
请不要添加自定义栏按钮项，使用默认行为。
不需要viewWillDisappear，不需要自定义BarButtonItem等…
最好是检测VC何时从其父对象中移除。
使用这两个函数中的任意一个
override func willMove(toParent parent: UIViewController?) {
super.willMove(toParent: parent)
if parent == nil {
callStatusDelegate?.backButtonClicked()//Here write your code
}
}
override func didMove(toParent parent: UIViewController?) {
super.didMove(toParent: parent)
if parent == nil {
callStatusDelegate?.backButtonClicked()//Here write your code
}
}
如果你想停止返回按钮的默认行为，然后添加自定义BarButtonItem。
在离开电流控制器之前，我需要显示警报。所以我是这样做的:
添加扩展UINavigationController与UINavigationBarDelegate 添加选择器到你的控制器导航
它的工作)
extension UINavigationController: UINavigationBarDelegate {
public func navigationBar(_ navigationBar: UINavigationBar, shouldPop item: UINavigationItem) -> Bool {
if let items = navigationBar.items, viewControllers.count < items.count {
return true
}
let clientInfoVC = topViewController as? ClientInfoVC
if clientInfoVC?.responds(to: #selector(clientInfoVC?.navigationShouldPopOnBack)) ?? false {
clientInfoVC?.navigationShouldPopOnBack(completion: { isAllowPop in
if isAllowPop {
DispatchQueue.main.async {
self.popViewController(animated: true)
}
}
})
}
DispatchQueue.main.async {
self.popViewController(animated: true)
}
return false
}
}
@objc func navigationShouldPopOnBack(completion: @escaping (Bool) -> ()) {
let ok = UIAlertAction(title: R.string.alert.actionOk(), style: .default) { _ in
completion(true)
}
let cancel = UIAlertAction(title: R.string.alert.actionCancel(), style: .cancel) { _ in
completion(false)
}
let alertController = UIAlertController(title: "", message: R.string.alert.contractMessage(), preferredStyle: .alert)
alertController.addAction(ok)
alertController.addAction(cancel)
present(alertController, animated: true, completion: nil)
}
将按钮替换为另一个答案中建议的自定义按钮可能不是一个好主意，因为您将失去默认的行为和样式。
另一个选择是在视图控制器上实现viewWillDisappear方法，并检查名为isMovingFromParentViewController的属性。如果那个属性为真，它意味着视图控制器正在消失，因为它正在被移除(弹出)。
应该是这样的:
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
if self.isMovingFromParentViewController {
// Your code...
}
}
在swift 4.2中
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
if self.isMovingFromParent {
// Your code...
}
}
