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;
}
这篇关于PrepareForSegue之谜的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！