我很难找到解决这个问题的好方法。在视图控制器的-viewWillDisappear:
方法中,我需要找到一种方法来确定它是否是因为视图控制器被推到导航控制器的堆栈上,或者是否因为视图控制器因弹出而消失。
目前我正在设置像isShowingChildViewController
这样的标志,但它变得相当复杂。我认为我可以检测它的唯一方法是使用-dealloc
方法。
您可以使用以下内容。
- (void)viewWillDisappear:(BOOL)animated {
[super viewWillDisappear:animated];
NSArray *viewControllers = self.navigationController.viewControllers;
if (viewControllers.count > 1 && [viewControllers objectAtIndex:viewControllers.count-2] == self) {
// View is disappearing because a new view controller was pushed onto the stack
NSLog(@"New view controller was pushed");
} else if ([viewControllers indexOfObject:self] == NSNotFound) {
// View is disappearing because it was popped from the stack
NSLog(@"View controller was popped");
}
}
当然,这是可能的,因为在调用viewWillDisappear时,UINavigationController的视图控制器堆栈(通过viewControllers属性公开)已经更新。
在iOS 6+中,Segues可以是一种非常有效的方法来处理这个问题。如果您在Interface Builder中为特定的segue指定了标识符,则可以在prepareForSegue
中检查它。
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if ([segue.identifier isEqualToString:@"LoginSegue"]) {
NSLog(@"Push");
// Do something specific here, or set a BOOL indicating
// a push has occurred that will be checked later
}
}
我假设您的意思是当您说要推入堆栈时,通过推送新视图将视图移动到导航控制器的堆栈中。我建议使用viewDidUnload
方法添加一个NSLog
语句来写一些东西到控制台,这样你就可以看到发生了什么,你可能想要添加一个NSLog
到viewWillDissappeer
。
这是一个类别来完成与sbrocket的答案相同的事情:
标题:
#import <UIKit/UIKit.h>
@interface UIViewController (isBeingPopped)
- (BOOL) isBeingPopped;
@end
资源:
#import "UIViewController+isBeingPopped.h"
@implementation UIViewController (isBeingPopped)
- (BOOL) isBeingPopped {
NSArray *viewControllers = self.navigationController.viewControllers;
if (viewControllers.count > 1 && [viewControllers objectAtIndex:viewControllers.count-2] == self) {
return NO;
} else if ([viewControllers indexOfObject:self] == NSNotFound) {
return YES;
}
return NO;
}
@end
我认为最简单的方法是:
- (void)viewWillDisappear:(BOOL)animated
{
if ([self isMovingFromParentViewController])
{
NSLog(@"View controller was popped");
}
else
{
NSLog(@"New view controller was pushed");
}
[super viewWillDisappear:animated];
}
迅速:
override func viewWillDisappear(animated: Bool)
{
if isMovingFromParentViewController
{
print("View controller was popped")
}
else
{
print("New view controller was pushed")
}
super.viewWillDisappear(animated)
}
来自UIViewController.h中的Apple文档:
“这四种方法可以在视图控制器的外观回调中使用,以确定它是作为子视图控制器呈现,关闭,还是添加或删除。例如,视图控制器可以检查它是否因为被解除而消失或通过检查表达式([self isBeingDismissed] || [self isMovingFromParentViewController])在其viewWillDisappear:方法中询问自己。“
- (BOOL)isBeingPresented NS_AVAILABLE_IOS(5_0);
- (BOOL)isBeingDismissed NS_AVAILABLE_IOS(5_0);
- (BOOL)isMovingToParentViewController NS_AVAILABLE_IOS(5_0);
- (BOOL)isMovingFromParentViewController NS_AVAILABLE_IOS(5_0);
所以是的,唯一记录的方法是通过以下方式:
- (void)viewWillDisappear:(BOOL)animated
{
[super viewWillDisappear:animated];
if ([self isBeingDismissed] || [self isMovingFromParentViewController]) {
}
}
Swift 3版本:
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
if self.isBeingDismissed || self.isMovingFromParentViewController {
}
}
如果你只是想知道你的视图是否会被弹出,我只是发现self.navigationController
是nil
中的viewDidDisappear
,当它从控制器堆栈中删除时。所以这是一个简单的替代测试。
(这是我在尝试各种其他扭曲之后发现的。我很惊讶没有导航控制器协议来注册视图控制器以便在pop上通知。你不能使用UINavigationControllerDelegate
,因为它实际上是真正的显示工作。)
斯威夫特4
override func viewWillDisappear(_ animated: Bool)
{
super.viewWillDisappear(animated)
if self.isMovingFromParent
{
//View Controller Popped
}
else
{
//New view controller pushed
}
}
在Swift中:
override func viewWillDisappear(animated: Bool) {
if let navigationController = self.navigationController {
if !contains(navigationController.viewControllers as! Array<UIViewController>, self) {
}
}
super.viewWillDisappear(animated)
}
我发现Apple的文档很难理解。此扩展程序有助于查看每个导航的状态。
extension UIViewController {
public func printTransitionStates() {
print("isBeingPresented=\(isBeingPresented)")
print("isBeingDismissed=\(isBeingDismissed)")
print("isMovingToParentViewController=\(isMovingToParentViewController)")
print("isMovingFromParentViewController=\(isMovingFromParentViewController)")
}
}
这个问题相当陈旧,但我偶然看到它,所以我想发布最佳实践(afaik)
你可以这样做
if([self.navigationController.viewControllers indexOfObject:self]==NSNotFound)
// view controller popped
}
这适用于iOS7,不知道它是否适用于任何其他的。据我所知,在viewDidDisappear
,观点已经突然出现。这意味着当你查询self.navigationController.viewControllers
时,你会得到一个nil
。所以,检查一下是否为零。
TL; DR
- (void)viewDidDisappear:(BOOL)animated
{
[super viewDidDisappear:animated];
if (self.navigationController.viewControllers == nil) {
// It has been popped!
NSLog(@"Popped and Gone");
}
}