{"id":124,"date":"2016-01-08T18:35:02","date_gmt":"2016-01-08T18:35:02","guid":{"rendered":"http:\/\/www.federicojacobi.com\/2\/?p=124"},"modified":"2016-01-08T18:35:02","modified_gmt":"2016-01-08T18:35:02","slug":"static-classes-on-wordpress-plugins","status":"publish","type":"post","link":"https:\/\/federicojacobi.com\/2016\/01\/08\/static-classes-on-wordpress-plugins\/","title":{"rendered":"Static classes on WordPress plugins"},"content":{"rendered":"

If you have a wordpress plugin, more than likely you are using add_action and\/or add_filter. No problem, until you get this error:<\/p>\n

Warning: call_user_func_array() expects parameter 1 to be a valid callback, cannot access self:: when no class scope is active in \/home\/wpcom\/public_html\/wp-includes\/plugin.php on line .........<\/pre>\n
One of the annoyances of wordpress is that tracking bugs when in actions or filters can be a bit of a hassle, but you don’t know where the error actually originated, but with a bit of grep-ing of searching you can find the issue. With the error above however, what’s going on is not so evident. Consider the following plugin that does nothing:<\/p>\n
final class doNothing {\n\tstatic $emptyString = '';\n\n\tstatic function init() {\n\t\tadd_action( 'wp_footer', array( self, 'output' ) );\n\t}\n\n\tstatic function output() {\n\t\t\/\/ Don't echo anything\n\t\techo self::$emptyString;\n\t}\n}\ndoNothing::init();<\/pre>\n
Nothing seems wrong here, however, it throws the warning above. The right way of doing this is:<\/p>\n
final class doNothing {\n\n\tstatic $emptyString = '';\n\n\tstatic function init() {\n\t\tadd_action( 'wp_footer', array( __CLASS__, 'output' ) );\n\t}\n\n\tstatic function output() {\n\t\t\/\/ Don't echo anything\n\t\techo self::$emptyString;\n\t}\n}\ndoNothing::init();<\/pre>\n
The key being __CLASS__<\/strong> instead of self<\/strong> on the add_action line. When using static classes add_action and add_filter don’t like self<\/strong> however, if your class is not static, therefore, instantiated you can use add_action( $this, ‘function’ )<\/span>\u00a0 no problem. Seems odd, but that’s how it is.<\/p>\n","protected":false},"excerpt":{"rendered":"
If you have a wordpress plugin, more than likely you are using add_action and\/or add_filter. No problem, until you get this error: Warning: call_user_func_array() expects parameter 1 to be a valid callback, cannot access self:: when no class scope is active in \/home\/wpcom\/public_html\/wp-includes\/plugin.php on line ……… One of the annoyances of wordpress is that tracking…  Read more »<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[11],"tags":[],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/federicojacobi.com\/wp-json\/wp\/v2\/posts\/124"}],"collection":[{"href":"https:\/\/federicojacobi.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/federicojacobi.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/federicojacobi.com\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/federicojacobi.com\/wp-json\/wp\/v2\/comments?post=124"}],"version-history":[{"count":0,"href":"https:\/\/federicojacobi.com\/wp-json\/wp\/v2\/posts\/124\/revisions"}],"wp:attachment":[{"href":"https:\/\/federicojacobi.com\/wp-json\/wp\/v2\/media?parent=124"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/federicojacobi.com\/wp-json\/wp\/v2\/categories?post=124"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/federicojacobi.com\/wp-json\/wp\/v2\/tags?post=124"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}