PHP error with shortcode handler from a class

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Currently i am using the following generic flow for adding the shortcode for a plugin. 

class MyPlugin {

    private $myvar;

    function baztag_func() {
        print $this->myvar;            
    }
}

add_shortcode( 'baztag', array('MyPlugin', 'baztag_func') );

Now when this class and it’s method are called i get the following error.

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Fatal error: Using $this when not in object context in …

(Line no is where i have printed the $this->myvar)

Is this a problem on WordPress’s end or is there is something i’m doing wrong? It seems to be something really simple.

Post Views: 6

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3 comments

  1. As the error says you need an instance of the class to use $this. There are at least three possibilities:

    Make everything static

    class My_Plugin
{
    private static $var = 'foo';

    static function foo()
    {
        return self::$var; // never echo or print in a shortcode!
    }
}
add_shortcode( 'baztag', array( 'My_Plugin', 'foo' ) );

    But that’s not real OOP anymore, just namespacing.

    Create a real object first

    class My_Plugin
{
    private $var = 'foo';

    public function foo()
    {
        return $this->var; // never echo or print in a shortcode!
    }
}

$My_Plugin = new My_Plugin;

add_shortcode( 'baztag', array( $My_Plugin, 'foo' ) );

    This … works. But you run into some obscure problems if anyone wants to replace the shortcode.

    So add a method to provide the class instance:

    final class My_Plugin
{
    private $var = 'foo';

    public function __construct()
    {
        add_filter( 'get_my_plugin_instance', [ $this, 'get_instance' ] );
    }

    public function get_instance()
    {
        return $this; // return the object
    }

    public function foo()
    {
        return $this->var; // never echo or print in a shortcode!
    }
}

add_shortcode( 'baztag', [ new My_Plugin, 'foo' ] );

    Now, when someone wants to get the object instance, s/he just has to write:

    $shortcode_handler = apply_filters( 'get_my_plugin_instance', NULL );

if ( is_a( $shortcode_handler, 'My_Plugin ' ) )
{
    // do something with that instance.
}

    Old solution: create the object in your class

    class My_Plugin
{
    private $var = 'foo';

    protected static $instance = NULL;

    public static function get_instance()
    {
        // create an object
        NULL === self::$instance and self::$instance = new self;

        return self::$instance; // return the object
    }

    public function foo()
    {
        return $this->var; // never echo or print in a shortcode!
    }
}

add_shortcode( 'baztag', array( My_Plugin::get_instance(), 'foo' ) );

  2. You can use like this, shortcode inside the Class

    class stockData{


    function __construct() {
        add_shortcode( 'your_shortcode_name', array( $this, 'showData' ) );
        //add_action('login_enqueue_scripts', array( $this,'my_admin_head'));
    }

    function showData(){
        return '<h1>My shortcode content</h1>' ;
    }
}

$object=new stockData();

    If you want access shortcode content from another class. You can do like this.

    class my_PluginClass {

  public function __construct( $Object ) {

    $test = add_shortcode( 'your_shortcode_name', array( $Object, 'your_method_name' ) );

  }

}

class CustomHandlerClass{

  public function your_method_name( $atts, $content ) {
     return '<h1>My shortcode content</h1>' ;
  }
}

$Customobject  = new CustomHandlerClass();
$Plugin         = new my_PluginClass( $Customobject );

  3. Make sure that you make an instance of your class before using it unless you are sure it’s supposed to be called statically. When you call a method statically, you don’t use any instances and therefore it doesn’t have access to any member variables or methods.