Question

我正在下载NSManagedObject。将NSString分配给该对象的valueForKey @“username”。接下来，我将该字符串分配给UITableView中的cell.textLabel.text，我得到一个异常。

以下是抛出异常的代码：

-(NSString *)fetchUserName
{
    if ([fetchedUserNameObject objectAtIndex:0]!= NULL)
    {
        recipientUser = (User*)(fetchedUserNameObject);
        NSString *userName = (NSString*)[recipientUser  valueForKey:@"username"];            
        return userName;
    }
 }

.....

      NSString *recipientUserName = [self fetchUserName]

...

- (IBAction)reviewButtonPressed:(UIBarButtonItem *)sender
{
    NSLog(@"Recipient UserName from Review Button %@", recipientUserName);

    PDReviewVC *modalVC = [self.storyboard instantiateViewControllerWithIdentifier:@"pdReview"];
    UINavigationController *navBar=[[UINavigationController alloc]initWithRootViewController:modalVC];

    modalVC.recipientUserName= self.recipientUserName;
    [self presentViewController:navBar animated:YES completion:NULL];

}

日志

2013-08-30 11:51:49.393 Time[1188:c07] Recipient UserName from Review Button (
        iphone3gs
    )

现在在PDReviewVC中：

·H

@property (nonatomic, retain) NSString * recipientUserName;

的.m

@synthesize recipientUserName;

... //的cellForRowAtIndexPath

if (indexPath.section == 0)
{
    cell.textLabel.text = recipientUserName;
}

我在cell.textLabel.text = recipientUserName;：

上收到以下错误

2013-08-30 11:51:54.679 Time[1188:c07] -[__NSArrayI isEqualToString:]: unrecognized selector sent to instance 0xb889390
2013-08-30 11:53:53.303 Time[1188:c07] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSArrayI isEqualToString:]: unrecognized selector sent to instance 0xb889390'
*** First throw call stack:

更新

NSLog代码如下：

if ([fetchedUserNameObject objectAtIndex:0]!= NULL)
{
    recipientUser = (User*)(fetchedUserNameObject);
    NSLog(@"User %@", recipientUser);
    NSString *userName = (NSString*)[recipientUser valueForKey:@"username"];
    NSLog (@"userName from fetchUserName: %@", userName);
    NSLog(@"%@", userName);

    return userName;

}
else return NULL;

的NSLog：

2013-08-30 12:36:29.495 Time[1341:c07] User (
    "<User: 0xa55cd60> (entity: User; id: 0xa5a0ae0 <x-coredata://3B273CFB-1CAA-4FA0-95DC-BA9420219380-1341-000007F42366B21A/User/piphone3gs> ; data: <fault>)"
)
2013-08-30 12:36:29.496 Time[1341:c07] userName from fetchUserName: (
    iphone3gs
)
2013-08-30 12:36:29.496 Time[1341:c07] (
    iphone3gs
)

Answer 1

您正在[recipientUser valueForKey:@"username"]投射NSString以使代码正常工作，而实际上它正在返回NSArray。删除强制转换(NSString*)并使代码正常工作，因此您实际上是从recipientUser中提取字符串而不是数组。

要进行调试，我建议您将日志记录更改为：

if ([fetchedUserNameObject objectAtIndex:0]!= NULL)
{
   recipientUser = (User*)(fetchedUserNameObject);
   NSArray *userNames = [recipientUser valueForKey:@"username"];
   for (int i=0; i < [userNames count]; i++) {
       NSLog(@"Username %i is %@", i, [userNames objectAtIndex:i]);
   }
}

Answer 2

您的问题的答案就在您的错误消息中。： - ）

它告诉您，您认为属于NSString类型的对象实际上是NSArray。因此，NSArray不响应任何名为isEqualToString的方法。

在你的fetchUserName方法中，你将一个对象转换为NSString并返回它，但显然你在这里得到一个NSArray。当您将此对象设置为标签的文本属性时，后台会发生一些事情，询问当前字符串属性是否等于您尝试设置的属性。然后，错误。

尝试在fetchUserName方法中return之前放置此行：

NSLog(@"%@",username);
return username;

然后使用此NSLog（）的控制台结果修改您的问题，我们可以帮助您弄清楚数组中的内容。

好的，在您返回用户名对象之前，请执行以下操作：

NSString *username;
id object = [recipient valueForKey:@"username"];
if ([object isKindOfClass:[NSString class]]) {
    username = (NSString *)object;
    return username;
} else if ([object isKindOfClass:[NSArray class]]) {
    NSArray *returnedArray = (NSArray *)object;
    if (returnedArray.count > 0) {
        id arrayMember = [returnedArray objectAtIndex:0];
        if ([arrayMember isKindOfClass:[NSString class]]) {
            username = (NSString *)arrayMember;
            return username;
        }
    }
}
return nil;

UITableView：cell.textLabel.text错误：[__ NSArrayI isEqualToString：]

2 个答案: