PrepareForSegue之谜

本文介绍了PrepareForSegue之谜的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我在两个不同的VC中有一个prepareForSegue方法。一个使用 if 语句，而另一个使用开关。代码几乎完全相同，但名称除外。

I've got a prepareForSegue method in two different VCs. One uses an if statement, while the other is intended to use a switch. The code is virtually identical, except for names.

这个工作正常：

- (void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender { NSManagedObjectContext *localContext = [NSManagedObjectContext MR_contextForCurrentThread]; if ([[segue identifier] isEqualToString:@"addActivity"]) { UINavigationController *navController = (UINavigationController *)segue.destinationViewController; AddActivityViewController *aavc = (AddActivityViewController *)navController.topViewController; aavc.delegate = self; ListActivity *addedActivity = (ListActivity *)[ListActivity MR_createInContext:localContext]; aavc.thisActivity = addedActivity; }

这个给了我两个警告。在第一行，我得到一个预期表达式警告。在第二行，我得到使用未声明的标识符'NavController'。

This one gives me two warnings. On the first line, I get an "Expected expression" warning. On the second line, I get "Use of undeclared identifier 'NavController'.

-(void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender { NSManagedObjectContext *localContext = [NSManagedObjectContext MR_contextForCurrentThread]; [SearchSpecs MR_truncateAllInContext:localContext]; [localContext MR_saveToPersistentStoreAndWait]; switch ([sender tag]) { case aVsAButton_tag: UINavigationController *navController = (UINavigationController *)segue.destinationViewController; AvsAViewController *aVSaVC = (AvsAViewController *)navController.topViewController; aVSaVC.delegate = self; SearchSpecs *thisSpec = (SearchSpecs *)[SearchSpecs MR_createInContext:localContext]; aVSaVC.currentSpec = thisSpec; break; default: break; } }

有人可以指出我的错误吗？

Can someone please point out my mistake?

谢谢！

修改：

问题由所有给出的答案修正，并且非常感谢所有人！

The problem was fixed by all the answers given, and many thanks for all!

这是我的新代码：

-(void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender { NSManagedObjectContext *localContext = [NSManagedObjectContext MR_contextForCurrentThread]; [SearchSpecs MR_truncateAllInContext:localContext]; [localContext MR_saveToPersistentStoreAndWait]; switch ([sender tag]) { case aVsAButton_tag: { UINavigationController *navController = (UINavigationController *)segue.destinationViewController; AvsAViewController *aVSaVC = (AvsAViewController *)navController.topViewController; aVSaVC.delegate = self; SearchSpecs *thisSpec = (SearchSpecs *)[SearchSpecs MR_createInContext:localContext]; aVSaVC.currentSpec = thisSpec; } break; default: break; } }

当我添加分号时根据第三个答案的建议，我在默认值行收到了Switch case in protected scope的警告。但是，当我将 case 代码括在大括号中时，所有问题都会消失。我记得很好的事情！

When I added the semi-colon per the suggestion of the third answer, I got the warning that "Switch case is in protected scope" at the default: line. However, when I enclosed the case code in curly brackets, all problems evaporated. Very good thing for me to remember!

我会检查所有的答案，但由于它们都是同时到达的，所以如果我接受，我希望没有人会被冒犯最佳。为所有人+1，再次感谢！

I would green-check all answers, but since they all arrived about simultaneously, I hope no one will be offended if I accept the top one. +1 for all, and thanks again!

推荐答案

在C / Objective-C中，你不能在switch语句中声明变量那。如果要声明变量以用于switch语句的特定情况，可以将该案例的所有代码放在语句块中：

In C/Objective-C, you cannot declare variables in a switch statement like that. If you want to declare variables for use in a specific case of a switch statement, you can put all the code for that case in a statement block:

switch ([sender tag]) { case aVsAButton_tag: { UINavigationController *navController = (UINavigationController *)segue.destinationViewController; AvsAViewController *aVSaVC = (AvsAViewController *)navController.topViewController; aVSaVC.delegate = self; SearchSpecs *thisSpec = (SearchSpecs *)[SearchSpecs MR_createInContext:localContext]; aVSaVC.currentSpec = thisSpec; } break; default: break; }