索引到数组字典时出现无法识别的选择器错误

【问题标题】：Unrecognized selector error when indexing into a dictionary of arrays索引到数组字典时出现无法识别的选择器错误
【发布时间】：2012-11-19 23:43:57
【问题描述】：

我有一个导致__NSCFDictionary objectAtIndex: 错误的数组字典。

谁能告诉我为什么？发生错误时，字典显然至少有 1 个数组。

 NSError *error;
 responseString = [[NSString alloc] initWithData:self.responseData2 encoding:NSUTF8StringEncoding];

/* response string contains this:
   {"words":
     {
    "word": {"rowsreturned":0,"id":"-1","date":"","word":"","term":"","definition":"","updated_on":""}
     },
    "status":"",
    "rowsreturned":""
  }
*/

 NSDictionary *json = [NSJSONSerialization JSONObjectWithData:self.responseData2 options:kNilOptions error:&error];

 NSArray *todaysWord = [[json objectForKey:@"words"] objectForKey:@"word"];

 //error here -[__NSCFDictionary objectAtIndex:]: unrecognized selector sent to instance
 NSDictionary *word = [todaysWord objectAtIndex:0];

【问题讨论】：

[[json objectForKey:@"words"] objectForKey:@"word"];正在返回字典而不是数组。尝试在该行之后添加一个 NSLog。你可以看到它

标签： objective-c ios json nsdictionary

【解决方案1】：

在您的情况下，[[json objectForKey:@"words"] objectForKey:@"word"]; 返回的是字典而不是数组。尝试执行以下操作，

id wordParam = [[json objectForKey:@"words"] objectForKey:@"word"];

if ([wordParam isKindOfClass:[NSArray class]]) {
  NSDictionary *word = [(NSArray *)wordParam objectAtIndex:0];
} else if ([wordParam isKindOfClass:[NSDictionary class]]) {
  NSDictionary *word = (NSDictionary *)wordParam;
} else {
  NSLog(@"error. %@ is not an array or dictionary", wordParam);
}

您的响应字符串还显示word 的值是，

{"rowsreturned":0,"id":"-1","date":"","word":"","term":"","definition":"","updated_on":""}

这是一个键值对为rowsreturned:0、id:-1等的字典。

【讨论】：