iphone 导航 Controller : wait for uialertview response before to quit the current view

Question

我有一个带有导航 Controller 管理的后退按钮的 View ，我想检查当用户单击后退按钮时文件是否已保存。如果文件已保存，您返回上一个 View ，否则 uialertview 会询问您是否要保存文件。

所以我这样做了，但是 View 消失了，之后出现了警报 View 。

-(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

当 viewWillDisappear 被调用时，已经太迟了。您应该早点拦截后退按钮。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(delegate):

// 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 中重新设置它:

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; 
}

然后在对话框的 YES 处理程序中，手动弹出 Controller :

[self.navigationController popViewController:YES];