"不支持多次推送相同的视图控制器实例"例外

Question

我使用以下代码检索一些消息并将它们放入我的收件箱.

MyInboxVC *inboxVC=[MyInboxVC get ];
//upload all the pending messages
UINavigationController *devNavController=[[MyappMgr get]getDeveloperNavigationController ];

[devNavController pushViewController:inboxVC animated:YES];
[devNavController setNavigationBarHidden:NO];

我得到了例外

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Pushing the same view controller instance more than once is not supported (<MyInboxVC: 0x1452a0>)'

这是什么意思？我究竟做错了什么？

Answer 1

我相信当你做一些非常快的动作时,这也会发生.我像这样建立一些东西:

if(![self.navigationController.topViewController isKindOfClass:[YOURCLASS class]]) {

编辑//

这种情况更常发生在动画速度较慢的旧设备上,如iphone 3或3gs

Answer 2

首先处理崩溃,所以它不会杀死你的应用程序:

@try {
    [self.navController pushViewController:viewController animated:NO];
} @catch (NSException * e) {
    NSLog(@"Exception: %@", e);
} @finally {
    //NSLog(@"finally");
}

然后,如果你得到错误,请使用popTo

- (void)pushViewController:(UIViewController *)viewController {
  if (viewController) {
    @try {
        [self.navController pushViewController:viewController animated:NO];
    } @catch (NSException * ex) {
        //“Pushing the same view controller instance more than once is not supported” 
        //NSInvalidArgumentException
        NSLog(@"Exception: [%@]:%@",[ex  class], ex );
        NSLog(@"ex.name:'%@'", ex.name);
        NSLog(@"ex.reason:'%@'", ex.reason);
        //Full error includes class pointer address so only care if it starts with this error
        NSRange range = [ex.reason rangeOfString:@"Pushing the same view controller instance more than once is not supported"];

        if ([ex.name isEqualToString:@"NSInvalidArgumentException"] &&
           range.location != NSNotFound) {
            //view controller already exists in the stack - just pop back to it
            [self.navController popToViewController:viewController animated:NO];
        } else {
            NSLog(@"ERROR:UNHANDLED EXCEPTION TYPE:%@", ex);
        }
    } @finally {
        //NSLog(@"finally");
    }
  } else {
    NSLog(@"ERROR:pushViewController: viewController is nil");
  }
}

Answer 3

这意味着ViewController返回[MyInboxVC get]的已经在导航堆栈中devNavController.您不能多次将相同的对象添加到堆栈.

显然,你之前已经MyInboxVC推过了.确保在不再需要时将其弹出.

这就是"它是什么意思"的答案,但没有足够的信息来知道你需要做些什么来解决它.

我的猜测是你的导航堆栈比你想象的要大得多,这意味着你不会像你想象的那样经常弹出.

Answer 4

这意味着您要推送相同的viewcontroller对象，以使其已经在其中。

[self.navigationController pushViewController:viewControllerObj animated:NO];

[self.navigationController pushViewController:viewControllerObj animated:NO];

检查您是否将您的代码推入了循环，还是您不小心将代码放置了不止一次。

Answer 5

你是作为segue的一部分表演的吗？如果是,则无需将VC推送到导航控制器,因为segue已经执行此操作.这就是您的错误发生的原因 - 您正在推送已经在NavController堆栈上的VC.