I'm building two mutually incompatible plugins. When either one is activated, the other must be deactivated. I'm using the code below to accomplish this.

It works fine the first time I upload and activate the second plugin, but if I try to activate the inactive plugin in the admin panel, it just deactivates both plugins. (Though I get a confirmation message saying "plugin activated." Liars!) I am then able to activate either one of the two plugins.

Any ideas what the problem is?

function deactivate_other_plugin() {
    if( is_plugin_active('plugin_folder/plugin_file.php') ) {
add_action( 'admin_init', array( $this, 'deactivate_other_plugin' ) );
  • 3
    Why would you want this? Expected behaviour is that a plugin would detect the other plugin and return early without doing anything except maybe putting an admin notice up. Also &$this is a hack to make things work on PHP4, you should use $this instead when registering functions as is customary in PHP 5 ( unless your plugin is aimed for a server stack from 2003 and WordPress v1.5 )
    – Tom J Nowell
    Feb 17, 2016 at 4:30
  • Ok, so it would be better to just return early and give a notice to deactivate the other plugin before activating. Thanks for the tip about &$this being obsolete.
    – j8d
    Feb 17, 2016 at 4:43

1 Answer 1


Ok, based on the comments, I decided to just prevent activation and send an admin notice instead.

add_action( 'admin_notices', 'lsmi_admin_notice' );
add_action( 'network_admin_notices', 'lsmi_admin_notice' );
function lsmi_admin_notice() {
    if( class_exists ( 'Location_Specific_Menu_Items_By_City' ) ){
        global $pagenow;
        if( $pagenow == 'plugins.php' ){
            deactivate_plugins ( 'lsmi-by-country/LSMI_Country.php' );
            if ( current_user_can( 'install_plugins' ) ) {
                echo '<div id="error" class="error notice is-dismissible"><p>Error. Please deactivate LSMI by City first and try again.</div>';

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