IOS 开发之NSDictionary转换成JSON字符串

NSError error;
NSData jsonData = [NSJSONSerialization dataWithJSONObject:self options:NSJSONWritingPrettyPrinted error:&error];
if (! jsonData) {
  return @"{}";
} else {
  return [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
}

NSError error = nil;
NSData jsonData = nil;
if (!self) {
  return nil;
}
NSMutableDictionary dict = [NSMutableDictionary dictionary];
[self enumerateKeysAndObjectsUsingBlock:^(id _Nonnull key, id _Nonnull obj, BOOL  _Nonnull s) {
  NSString keyString = nil;
  NSString valueString = nil;
  if ([key isKindOfClass:[NSString class]]) {
    keyString = key;
  }else{
    keyString = [NSString stringWithFormat:@"%@",key];
  }

  if ([obj isKindOfClass:[NSString class]]) {
    valueString = obj;
  }else{
    valueString = [NSString stringWithFormat:@"%@",obj];
  }

  [dict setObject:valueString forKey:keyString];
}];
jsonData = [NSJSONSerialization dataWithJSONObject:dict options:NSJSONWritingPrettyPrinted error:&error];
if ([jsonData length] == 0 || error != nil) {
  return nil;
}
NSString jsonString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
return jsonString;