include function xy() of a wordpress plugin

I want to build a WordPress a开发者_C百科dmin dashboard widget which should return some information from another plugin.

This dashboard widget should read the functions of this plugin here: http://plugins.svn.wordpress.org/wp-document-revisions/trunk/wp-document-revisions.php

So my code is:

include (WP_PLUGIN_URL.'/wp-document-revisions/wp-document-revisions.php');
$file_type = get_file_type('3'); 

But this doesn't work. These are the errors:

Fatal error: Call to undefined function add_action() in /.../wp-content/plugins/wp-document-revisions/wp-document-revisions.php on line 26

Fatal error: Call to undefined function get_file_type() in /.../wp-content/plugins/dashboard-widget/dashboard-widget.php

Can anyone tell me how I have to do this, that I can read the function get_file_type('3')?

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I'm assuming you are navigating straight to your PHP file in the wp-content/plugins/ folder rather than using a stub to create a URL. If this is the case, then you probably forgot to include wp-load.php

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You should not include the plugin file (since the plugin may not be installed or activated). Instead of this you should check if the function exists:

if (function_exists('get_file_type')) {
 $file_type = get_file_type('3'); 
 // rest of the code of the widget
}

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It sounds like you are trying to access the PHP file directly, rather than going through WordPress proper. You should create a plugin, and hook into the Dashboard Widgets API.

As for implementation with WP Document Revisions, you've got two options. As of version 1.2, get_documents() and get_document_revisions() are two global functions that will be accessible anytime after the plugins_loaded hook. The FAQ has a bit more info, but they basically function like the native get_posts() function.

Alternatively, the class should be available globally as $wpdr. So if you wanted, for example, to call get_latest_version( 1 ) it'd be $wpdb->get_latest_version( 1 ).

Both assume the plugin's already activated. If you simply include the file, you're going to get an error that you're trying to redeclare the WP_Document_Revisions class.

If you do create a dashboard, I'd love to include it in future releases of the plugin!