PHP error with shortcode handler from a class

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.

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.

Answers:

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Method 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' ) );

Method 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 );

Method 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.

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0