Question

我有以下

// this code is inside cellForRowAtIndexPath for a TableViewController

id answer = [self.answers objectAtIndex:indexPath.row];
if ([answer respondsToSelector:@selector(objectForKey)]) {
    cell.textLabel.text = [answer valueForKey:@"answer_id"];
} else {
    // I'm ending up here, instead of the cell.textLabel being set
    [NSException raise:@"Answer is of invalid class" format:@"It should be able to respond to valueForKey, class: %@", [answer class]];
}

其中self.answers设置为

// the question that gets passed here is a parsed single object 
// from the `/questions` path
- (NSArray *)answersForQuestion:(NSDictionary *)question {
    NSString *contents = [self loadContentsForPath:[question valueForKey:@"question_answers_url"]];
valueForKey:@"question_answers_url"]];
    NSDictionary *data = [contents JSONValue];
    NSArray *answers = [data valueForKey:@"answers"];
    return answers;
}

- (NSString *)loadContentsForPath:(NSString *)path {
    NSString *wholeURL = [@"http://api.stackoverflow.com/1.1" stringByAppendingString:path];    
    return [NSString stringWithContentsOfURL:[NSURL URLWithString:wholeURL] encoding:NSUTF8StringEncoding error:nil];
}

我正在为加载问题做同样的事情，但这看起来很好当我尝试[answers valueForKey:@"answer_id"]时，答案失败。

我认为这不是JSON解析器的问题，因为它适用于/questions数据。

当调试器停止异常并且我尝试右键单击时 - ＆gt;在answers打印说明，我得到了

Printing description of answer:
<CFBasicHash 0x6ec1ec0 [0x1474b38]>{type = mutable dict, count = 13,
entries =>
    1 : <CFString 0x6ec57d0 [0x1474b38]>{contents = "down_vote_count"} = <CFNumber 0x6e1dc00 [0x1474b38]>{value = +0, type = kCFNumberSInt32Type}
    2 : <CFString 0x6ec4ee0 [0x1474b38]>{contents = "last_activity_date"} = <CFNumber 0x6ec5780 [0x1474b38]>{value = +1326379080, type = kCFNumberSInt64Type}
    3 : <CFString 0x6ec44b0 [0x1474b38]>{contents = "community_owned"} = <CFBoolean 0x1474f68 [0x1474b38]>{value = false}
...

对我而言似乎是一个常规哈希。我试过了objectForKey和valueForKey这两个都没有用，即

exception 'NSInvalidArgumentException', reason: '-[__NSCFNumber isEqualToString:]: unrecognized selector sent to instance 0x6b2a330'

当我做的时候

cell.textLabel.text = [answer objectForKey:@"answer_id"];

Answer 1

实际上，堆栈溢出的api会发回一个数字。也就是说，为密钥answer_id存储的值是字典中的NSNumber，而不是NSString，您应该相应地对待它。

Answer 2

:是方法名称的一部分，因此您需要执行以下操作：

if ([answer respondsToSelector:@selector(objectForKey:)]) {

然后使用objectForKey:，而不是valueForKey:。第一种是访问字典中的对象，后者是所谓的键值编码。所以它是：

id answer = [self.answers objectAtIndex:indexPath.row];
if ([answer respondsToSelector:@selector(objectForKey:)]) {
    cell.textLabel.text = [answer objectForKey:@"answer_id"];
} else {
    [NSException raise:@"Answer is of invalid class" format:@"It should be able to respond to objectForKey:, class: %@", [answer class]];
}

最后但并非最不重要的是，您从answer字典中获取的对象看起来像是NSNumber，而不是NSString。因此，您可能希望将文本设置更改为：

cell.textLabel.text = [[answer objectForKey:@"answer_id"] description];

Answer 3

你可以使用： -

NSDictionary *answer = [self.answers objectAtIndex:indexPath.row];
if ([answer respondsToSelector:@selector(objectForKey)]) {
    cell.textLabel.text = [answer valueForKey:@"answer_id"];
} else {
    [NSException raise:@"Answer is of invalid class" format:@"It should be able to respond to valueForKey, class: %@", [answer class]];
}

或

id answer = [self.answers objectAtIndex:indexPath.row]; if (answer isKindOfClass:[NSDictionary class]) { cell.textLabel.text = [answer valueForKey:@"answer_id"]; } else { // I'm ending up here, instead of the cell.textLabel being set [NSException raise:@"Answer is of invalid class" format:@"It should be able to respond to valueForKey, class: %@", [answer class]]; }

NSDictionary没有响应objectForKey和valueForKey

3 个答案: