iphone navigationController：在退出當前視圖之前等待uialertview響應

Question

我有一個視圖，帶有一個導航控制器管理的後退按鈕，我想檢查用戶單擊後退按鈕時是否保存了文件。 如果文件已保存，則返回上一個視圖，否則uialertview會詢問您是否要保存該文件。

所以我做到了，但視圖disapear和alertview後出現。

​​

Answer 1

當viewWillDisappear被調用時，已經太晚了。你應該在之前攔截後退按鈕。我從來沒有做過，但我的建議是設置上的導航欄屬性代表在viewDidAppear方法：

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

self.navigationController.navigationBar.delegate = self; 

不要忘記設置回在viewWillDisappear：

self.navigationController.navigationBar.delegate = prevNavigationBarDelegate; 

然後攔截該方法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; 
} 

而在該對話框的YES處理程序中，手動彈出，所述控制器：

[self.navigationController popViewController:YES]; 

Answer 2

您必須繼承UINavigationController以使其工作。然後覆蓋 - （BOOL）navigationBar：（UINavigationBar *）navigationBar shouldPopItem：（UINavigationItem *）項目。 您應該設置視圖控制器採用的自定義委託協議，如果允許它彈出，請調用您的[super navigationBar shouldPopItem：]，否則返回上述方法的NO。

Answer 3

那豈不是更容易只是左鍵項目添加如下所示：

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

Answer 4

要跟進諾佈雷響應和喬恩mentionned它，最好的辦法是子類的UINavigationController。

最簡單的方式和以達致這最快的方式：

1. 修改類在界面生成的導航控制器的從CustomNavigationControllerDelegate繼承

在您的UIViewController中實現CustomNavigationControllerDelegate協議

@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; 
} 

註冊你的控制器作爲代表

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

最後的和重要的部分，刪除委託（以避免在彈出窗口重新觸發自己），並自己彈出控制器在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邊，希望能有所幫助。

---

這裏有來源：

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