1.字典
NSMutableDictionary *dicFriends = [[NSMutableDictionary alloc] init];
[dicFriends setObject:friends forKey:@"usernames"];
NSData *dataFriends = [NSJSONSerialization dataWithJSONObject:dicFriends options:NSJSONWritingPrettyPrinted error:nil];
NSString *jsonString = [[NSString alloc] initWithData:dataFriends
encoding:NSUTF8StringEncoding];
（ps? usernames 是字段揍愁，jsonString是轉(zhuǎn)換json格式的字典）
2.數(shù)組
數(shù)組其實和字典一樣带兜，只需將（dataWithJSONObject：dicFriends）參數(shù)刹衫，換成數(shù)組就可以了
