How to put drop down list of content type page in to another content type pages

Question

I have crated two content type like A and B .some of field are similar .I don't want to repeat that field .I want to put drop down list on any one of A or B.

Answer 1

YOU should use the entity reference module for the above purpose.

Provides a field type that can reference arbitrary entities:

A generic entity reference field Four widgets: Two implemented on top of the Options module (Select and Radios/Checkboxes), Two autocomplete widgets (one with one text field per entry, one tag-style with comma-separated entries in the same text field) Two formatters: A "Label" formatter, with optional link that displays the label of the referenced entity (the node title, the user name, etc.) A "Rendered entity" formatter, that renders the references entity using a configurable view mode Integration with Views (for both forward and backward references) Integration with Entity Metadata (and as a consequence with Search API and the like) Integration with Devel generate Integration with Feeds and Migrate (>= 2.3) for painless data import This modules depends on Entity API and CTools.

Modules extending Entity reference functionality:

Earlier answer deleted following comments :
If you want to use the existing field then just go to manage fields tab under
Home » Administration » Structure » Content types » A
and use existing field option where you will get the existing field of other content type
Check the image below for existing field option :

Or else you can do it in the following way :

You can get your dropdown list for content type in $form_state['values']['your_field_name_for_dropdown'] and
and Save that value in $_SESSION['module_name']['your_field_name_for_dropdown'] After saving that value you can use that value to insert into another content type in the hook_form_alter function or your custom_form itself.

Answer 2

Simply go to /admin/structure/types/manage/<your-content-type>/fields and at the end of page you will find a 2 options : Add new field, and Add existing field

Use Add existing field to add a field from one content type in another content type.