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

Question

我有一个带有导航控制器管理的后退按钮的视图,我想检查用户单击后退按钮时是否已保存文件.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文件.

所以我这样做了,但视图消失了,警报视图出现了.

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

- (void)alertView:(UIAlertView *)alertView didDismissWithButtonIndex:(NSInteger)buttonIndex
{
switch (buttonIndex) {
    case 0:
        NSLog(@"NO");
        break;
    case 1:
        NSLog(@"yes");
        break;
    default:
        break;
}
}

Answer 1

调用viewWillDisappear时,已经太晚了.您应该在之前拦截后退按钮.我从来没有这样做过,但我的建议是在viewDidAppear方法中的navigationBar属性上设置委托:

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

self.navigationController.navigationBar.delegate = self;

不要忘记在viewWillDisappear中将其设置回来:

self.navigationController.navigationBar.delegate = prevNavigationBarDelegate;

然后拦截shouldPopItem方法:

- (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; 
}

在对话框的YES处理程序中,手动弹出控制器:

[self.navigationController popViewController:YES];