iphone navigationController：在退出当前视图之前等待uialertview响应

Question

我有一个视图，带有一个导航控制器管理的后退按钮，我想检查用户单击后退按钮时是否保存了文件。 如果文件已保存，则返回上一个视图，否则uialertview会询问您是否要保存该文件。

所以我做到了，但视图disapear和alertview后出现。

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Answer 1

当viewWillDisappear被调用时，已经太晚了。你应该在之前拦截后退按钮。我从来没有做过，但我的建议是设置上的导航栏属性代表在viewDidAppear方法：

// save the previous delegate (create an ivar for that) 
prevNavigationBarDelegate = self.navigationController.navigationBar.delegate; 

self.navigationController.navigationBar.delegate = self; 

不要忘记设置回在viewWillDisappear：

self.navigationController.navigationBar.delegate = prevNavigationBarDelegate; 

然后拦截该方法shouldPopItem：

- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item { 
    if(!self.fileSaved) { 
     UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"" message:@"Save the file?" delegate:self cancelButtonTitle:@"No" otherButtonTitles:@"Yes",nil]; 
     [alert show]; 
     [alert release]; 

     return NO; 
    } 

    if ([prevNavigationBarDelegate respondsToSelector:@selector(navigationBar:shouldPopItem:)]) 
     return [prevNavigationBarDelegate navigationBar:navigationBar shouldPopItem:item]; 

    return YES; 
} 

而在该对话框的YES处理程序中，手动弹出，所述控制器：

[self.navigationController popViewController:YES]; 

Answer 2

您必须继承UINavigationController以使其工作。然后覆盖 - （BOOL）navigationBar：（UINavigationBar *）navigationBar shouldPopItem：（UINavigationItem *）项目。 您应该设置视图控制器采用的自定义委托协议，如果允许它弹出，请调用您的[super navigationBar shouldPopItem：]，否则返回上述方法的NO。

Answer 3

那岂不是更容易只是左键项目添加如下所示：

UIBarButtonItem *backButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemSave target:self action:@selector(saveThisDate)]; 
self.navigationItem.leftBarButtonItem = backButton; 
[backButton release]; 

Answer 4

要跟进诺布雷响应和乔恩mentionned它，最好的办法是子类的UINavigationController。

最简单的方式和以达致这最快的方式：

1. 修改类在界面生成的导航控制器的从CustomNavigationControllerDelegate继承

在您的UIViewController中实现CustomNavigationControllerDelegate协议

@interface YourViewController <CustomNavigationControllerDelegate>

#pragma mark - UINavigationBar Delegate Methods 
- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item { 

    UIAlertView* alert = [[UIAlertView alloc] initWithTitle:title message:message delegate:self cancelButtonTitle:cancel otherButtonTitles:ok, nil]; 
    alert.tag = kpopup_back; 
    [alert show]; 

    return NO; 
} 

注册你的控制器作为代表

#pragma mark - viewWillAppear - (void) viewWillAppear:(BOOL)animated { ((CustomNavigationController*)self.navigationController).customDelegate = self; }

最后的和重要的部分，删除委托（以避免在弹出窗口重新触发自己），并自己弹出控制器在UIAlertViewDelegate

case kpopup_back : { if(buttonIndex != 0) //OK { ((CustomNavigationController*)self.navigationController).customDelegate = nil; [self.navigationController popViewControllerAnimated:YES]; } } break;

它完美的作品在我的身边，希望能有所帮助。

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这里有来源：

CustomNavigationControllerDelegate.h

#import <UIKit/UIKit.h> 

@protocol CustomNavigationControllerDelegate <NSObject> 
@optional 
- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item; 
@end 

@interface CustomNavigationController : UINavigationController 

@property (nonatomic, retain) id<CustomNavigationControllerDelegate> customDelegate; 

@end 

CustomNavigationControllerDelegate.m

#import "CustomNavigationController.h" 

@interface CustomNavigationController() 

@end 

@implementation CustomNavigationController 

- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item { 

    if (_customDelegate && [_customDelegate respondsToSelector:@selector(navigationBar:shouldPopItem:)]) { 
     return [_customDelegate navigationBar:navigationBar shouldPopItem:item]; 
    } 

    return YES; 
} 

@end