how to get list of field names by select its node type in drupal? I got the all node type list in a variable using get_node_type_info() and now am passing this variable to field_info_instances as:

array_keys(field_info_instances("node", $op_keys));


ps: $op_keys is the variable to get node types.
But this is giving me list of node_type "keys" and I want field "keys".

Either tell: 


  (1)how to pass list of all node types as a $bundle_name in
  field_info_instances() ?


or


  (2) when selecting any of the node_type (as an option of select
  list) from select list, it's corresponding field's name will get
  rendered. I mean to say for example: node_type = "Article" and its
  field names  = "body", "title", "image". when "article" got
  clicked from select list, "body", "title", "image" should get
  rendered.
To get a list of field names for each content type,, stored in a variable "list", given an array of bundle names, you could do:

$list = array();
foreach($bundle_names as $bundle){
   $list[$bundle] = array_keys(field_info_instances('node', $bundle));
}

Hope that helps.