我已将视图推到导航控制器上,当我按下后退按钮时,它会自动转到上一个视图。我想在按下后退按钮之前做一些事情,然后再将视图弹出堆栈。哪个是后退按钮回调功能?
William Jockusch的answer用简单的技巧解决了这个问题。
-(void) viewWillDisappear:(BOOL)animated {
if ([self.navigationController.viewControllers indexOfObject:self]==NSNotFound) {
// back button was pressed. We know this is true because self is no longer
// in the navigation stack.
}
[super viewWillDisappear:animated];
}
也许这有点太晚了,但我之前也想要同样的行为。我使用的解决方案在App Store上的一个应用程序中运行良好。由于我没有看到任何人使用类似的方法,我想在这里分享。这个解决方案的缺点是它需要继承UINavigationController
。虽然使用Method Swizzling可能有助于避免这种情况,但我没有那么做。
因此,默认后退按钮实际上由UINavigationBar
管理。当用户点击后退按钮时,UINavigationBar
会询问其代表是否应该通过调用UINavigationItem
弹出顶部navigationBar(_:shouldPop:)
。 UINavigationController
实际上实现了这一点,但它没有公开声明它采用UINavigationBarDelegate
(为什么!?)。要拦截此事件,请创建UINavigationController
的子类,声明其与UINavigationBarDelegate
的一致性并实现navigationBar(_:shouldPop:)
。如果应该弹出顶部项目,请返回true
。如果它应该留下来返回false
。
有两个问题。首先,你必须在某个时候调用UINavigationController
版本的navigationBar(_:shouldPop:)
。但UINavigationBarController
没有公开声明它与UINavigationBarDelegate
的一致性,试图调用它将导致编译时错误。我使用的解决方案是使用Objective-C运行时直接获取实现并调用它。如果有人有更好的解决方案,请告诉我。
另一个问题是,如果用户点击后退按钮,navigationBar(_:shouldPop:)
首先被popViewController(animated:)
调用。如果通过调用popViewController(animated:)
弹出视图控制器,则顺序会反转。在这种情况下,我使用布尔值来检测popViewController(animated:)
是否在navigationBar(_:shouldPop:)
之前被调用,这意味着用户已经点击了后退按钮。
此外,我对UIViewController
进行了扩展,让导航控制器询问视图控制器是否应该弹出,如果用户点击后退按钮。视图控制器可以返回false
并执行任何必要的操作,稍后再调用popViewController(animated:)
。
class InterceptableNavigationController: UINavigationController, UINavigationBarDelegate {
// If a view controller is popped by tapping on the back button, `navigationBar(_:, shouldPop:)` is called first follows by `popViewController(animated:)`.
// If it is popped by calling to `popViewController(animated:)`, the order reverses and we need this flag to check that.
private var didCallPopViewController = false
override func popViewController(animated: Bool) -> UIViewController? {
didCallPopViewController = true
return super.popViewController(animated: animated)
}
func navigationBar(_ navigationBar: UINavigationBar, shouldPop item: UINavigationItem) -> Bool {
// If this is a subsequence call after `popViewController(animated:)`, we should just pop the view controller right away.
if didCallPopViewController {
return originalImplementationOfNavigationBar(navigationBar, shouldPop: item)
}
// The following code is called only when the user taps on the back button.
guard let vc = topViewController, item == vc.navigationItem else {
return false
}
if vc.shouldBePopped(self) {
return originalImplementationOfNavigationBar(navigationBar, shouldPop: item)
} else {
return false
}
}
func navigationBar(_ navigationBar: UINavigationBar, didPop item: UINavigationItem) {
didCallPopViewController = false
}
/// Since `UINavigationController` doesn't publicly declare its conformance to `UINavigationBarDelegate`,
/// trying to called `navigationBar(_:shouldPop:)` will result in a compile error.
/// So, we'll have to use Objective-C runtime to directly get super's implementation of `navigationBar(_:shouldPop:)` and call it.
private func originalImplementationOfNavigationBar(_ navigationBar: UINavigationBar, shouldPop item: UINavigationItem) -> Bool {
let sel = #selector(UINavigationBarDelegate.navigationBar(_:shouldPop:))
let imp = class_getMethodImplementation(class_getSuperclass(InterceptableNavigationController.self), sel)
typealias ShouldPopFunction = @convention(c) (AnyObject, Selector, UINavigationBar, UINavigationItem) -> Bool
let shouldPop = unsafeBitCast(imp, to: ShouldPopFunction.self)
return shouldPop(self, sel, navigationBar, item)
}
}
extension UIViewController {
@objc func shouldBePopped(_ navigationController: UINavigationController) -> Bool {
return true
}
}
在您查看控制器时,实现shouldBePopped(_:)
。如果您没有实现此方法,则默认行为是在用户点击后退按钮时立即弹出视图控制器。
class MyViewController: UIViewController {
override func shouldBePopped(_ navigationController: UINavigationController) -> Bool {
let alert = UIAlertController(title: "Do you want to go back?",
message: "Do you really want to go back? Tap on \"Yes\" to go back. Tap on \"No\" to stay on this screen.",
preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "No", style: .cancel, handler: nil))
alert.addAction(UIAlertAction(title: "Yes", style: .default, handler: { _ in
navigationController.popViewController(animated: true)
}))
present(alert, animated: true, completion: nil)
return false
}
}
你可以看看我的演示here。
这是它在Swift中对我有用的东西:
override func viewWillDisappear(_ animated: Bool) {
if self.navigationController?.viewControllers.index(of: self) == nil {
// back button pressed or back gesture performed
}
super.viewWillDisappear(animated)
}
如果你正在使用一个故事板并且你来自推送segue,你也可以覆盖shouldPerformSegueWithIdentifier:sender:
。
在我看来,最好的解决方案。
- (void)didMoveToParentViewController:(UIViewController *)parent
{
if (![parent isEqual:self.parentViewController]) {
NSLog(@"Back pressed");
}
}
但它只适用于iOS5 +
覆盖后退按钮可能更好,这样您就可以在弹出视图之前处理事件,例如用户确认。
在viewDidLoad中创建一个UIBarButtonItem并将self.navigationItem.leftBarButtonItem设置为传递给它的sel
- (void) viewDidLoad
{
// change the back button to cancel and add an event handler
UIBarButtonItem *backButton = [[UIBarButtonItem alloc] initWithTitle:@”back”
style:UIBarButtonItemStyleBordered
target:self
action:@selector(handleBack:)];
self.navigationItem.leftBarButtonItem = backButton;
[backButton release];
}
- (void) handleBack:(id)sender
{
// pop to root view controller
[self.navigationController popToRootViewControllerAnimated:YES];
}
然后你可以做一些事情,如提升UIAlertView来确认动作,然后弹出视图控制器等。
或者,不是创建新的后退按钮,而是可以符合UINavigationController委托方法,以便在按下后退按钮时执行操作。
我最终得到了这个解决方案。当我们点击后退按钮viewDidDisappear方法调用时。我们可以通过调用返回true的isMovingFromParentViewController选择器来检查。我们可以传回数据(使用Delegate).hope这可以帮助某人。
-(void)viewDidDisappear:(BOOL)animated{
if (self.isMovingToParentViewController) {
}
if (self.isMovingFromParentViewController) {
//moving back
//pass to viewCollection delegate and update UI
[self.delegateObject passBackSavedData:self.dataModel];
}
}
这是检测此问题的正确方法。
- (void)willMoveToParentViewController:(UIViewController *)parent{
if (parent == nil){
//do stuff
}
}
在推送视图时也会调用此方法。所以检查parent == nil是用于从堆栈弹出视图控制器
对于“BEFORE弹出堆栈视图”:
- (void)willMoveToParentViewController:(UIViewController *)parent{
if (parent == nil){
NSLog(@"do whatever you want here");
}
}
有一种比询问viewControllers更合适的方法。您可以使控制器成为具有后退按钮的navigationBar的委托。这是一个例子。在您要处理按下后退按钮的控制器的实现中,告诉它它将实现UINavigationBarDelegate协议:
@interface MyViewController () <UINavigationBarDelegate>
然后在初始化代码中的某个地方(可能在viewDidLoad中)使您的控制器成为其导航栏的委托:
self.navigationController.navigationBar.delegate = self;
最后,实现shouldPopItem方法。按下后退按钮时会调用此方法。如果堆栈中有多个控制器或导航项,您可能想要检查哪些导航项被弹出(item参数),以便您只在预期时执行自定义操作。这是一个例子:
-(BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item
{
NSLog(@"Back button got pressed!");
//if you return NO, the back button press is cancelled
return YES;
}
如果您不能使用“viewWillDisappear”或类似的方法,请尝试子类UINavigationController。这是标题类:
#import <Foundation/Foundation.h>
@class MyViewController;
@interface CCNavigationController : UINavigationController
@property (nonatomic, strong) MyViewController *viewController;
@end
实施班:
#import "CCNavigationController.h"
#import "MyViewController.h"
@implementation CCNavigationController {
}
- (UIViewController *)popViewControllerAnimated:(BOOL)animated {
@"This is the moment for you to do whatever you want"
[self.viewController doCustomMethod];
return [super popViewControllerAnimated:animated];
}
@end
另一方面,您需要将此viewController链接到您的自定义NavigationController,因此,在常规viewController的viewDidLoad方法中执行以下操作:
@implementation MyViewController {
- (void)viewDidLoad
{
[super viewDidLoad];
((CCNavigationController*)self.navigationController).viewController = self;
}
}
这是我实现的另一种方式(没有使用unwind segue测试它,但它可能不会像其他人在本页中的其他解决方案中所说的那样区分)让父视图控制器在子VC推送之前执行操作从视图堆栈中弹出(我从原始的UINavigationController中使用了几个级别)。这也可以用于在推送childVC之前执行操作。这具有使用iOS系统后退按钮的附加优势,而不必创建自定义UIBarButtonItem或UIButton。
UINavigationControllerDelegate
协议并注册委托消息:
MyParentViewController : UIViewController <UINavigationControllerDelegate>
-(void)viewDidLoad {
self.navigationcontroller.delegate = self;
}
UINavigationControllerDelegate
中实现这个MyParentViewController
实例方法:
- (id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController animationControllerForOperation:(UINavigationControllerOperation)operation fromViewController:(UIViewController *)fromVC toViewController:(UIViewController *)toVC {
// Test if operation is a pop; can also test for a push (i.e., do something before the ChildVC is pushed
if (operation == UINavigationControllerOperationPop) {
// Make sure it's the child class you're looking for
if ([fromVC isKindOfClass:[ChildViewController class]]) {
// Can handle logic here or send to another method; can also access all properties of child VC at this time
return [self didPressBackButtonOnChildViewControllerVC:fromVC];
}
}
// If you don't want to specify a nav controller transition
return nil;
}
UINavigationControllerDelegate
实例方法中指定了特定的回调函数
-(id <UIViewControllerAnimatedTransitioning>)didPressBackButtonOnAddSearchRegionsVC:(UIViewController *)fromVC {
ChildViewController *childVC = ChildViewController.new;
childVC = (ChildViewController *)fromVC;
// childVC.propertiesIWantToAccess go here
// If you don't want to specify a nav controller transition
return nil;
}