ios NSDictionary 从键中检索值时出现问题

Question

我有以下几行：

NSDictionary *JSON = [NSJSONSerialization JSONObjectWithData:responseObject options:NSJSONReadingAllowFragments error:&error];
if (error) {
    NSLog(@"Error serializing %@", error);
}
NSLog(@"JSOND: %@", JSON);
NSString *valueFromKey = [JSON objectForKey:@"backseatBucks"];

NSLog(valueFromKey);
NSLog(valueFromKey.class);

第一个 NSLog 将打印：

JSOND: {
backseatBucks = 5;
}

然而它似乎在 *valueFromKey 行出错，因为下面的 2 个打印语句没有被执行。下面列出了错误 - 任何帮助表示赞赏：

2015-04-23 17:32:35.382 BackseatDriver2[3554:113938] JSOND: {
backseatBucks = 5;
}
2015-04-23 17:32:35.383 BackseatDriver2[3554:113938] -[__NSCFNumber length]: unrecognized selector sent to instance 0x7a64a810
2015-04-23 17:32:35.384 BackseatDriver2[3554:113938] *** Terminating app due     to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFNumber length]: 
unrecognized selector sent to instance 0x7a64a810'

注意：我已经按照建议设置了符号断点，但我仍然很困惑为什么会收到此错误

Answer 1

那是因为字典包含一个NSNumber。这样做：

NSNumber *value = [JSON objectForKey:@"backseatBucks"];

ios NSDictionary 从键中检索值时出现问题

ios issue with NSDictionary retrieving value from key

ios

objective-c

nsdictionary