wordpress plugin is not activating from widget

Question

I am just creating a plugin in wordpress. In this plugin I am trying to create a widget, In that widget it will show a title, input text and text area in the widget section and when the values will be entered it will show to the site frontend. For that my code is like this

<?php
/*
Plugin Name: WP Simple Plugin
Plugin URI: http://www.wordpress.org
Description: A Plugin to show simple text in widget
Version: 0.1
Author: 
*/

class wp_my_plugin extends WP_Widget {
// constructor
    function wp_my_plugin() {
        parent::WP_Widget(false, $name = __('My Widget', 'wp_widget_plugin') );
    }

   function form($instance) {
    if($instance) {
      $title = esc_attr($instance['title']);
      $text = esc_attr($instance['text']);
      $textarea = esc_attr($instance['textarea']);
    } else {
      $title = '';
      $text = '';
      $textarea = '';
    }
    ?>
    <p>
      <label for="<?php echo $this->get_field_id('title'); ?>"><?php _e('Widget Title', 'wp_widget_plugin'); ?></label>
      <input class="widefat" type="text" id="<?php echo $this->get_field_id('title'); ?>" name="<?php echo $this->get_field_name('title');?>" value="<?php echo $title; ?>"/>
    </p>
    <p>
      <label for="<?php echo $this->get_field_id('text')?>"><?php _e('Text', 'wp_widget_plugin');?></label>
      <input type="text" class="widefat" name="<?php echo $this->get_field_name('text');?>" id="<?php echo get_field_id('text');?>" value="<?php echo $text; ?>" />
    </p>
    <p>
      <label for="<?php echo $this->get_field_id('textarea');?>"><?php _e('Textarea','wp_widget_plugin'); ?></label>
      <textarea name="<?php echo $this->get_field_name('textarea'); ?>" id="<?php echo $this->get_field_id('textarea'); ?>" class="widefat"  /><?php echo $textarea; ?></textarea>
    </p>

  <?php
  }

  function update($new_instance, $old_instance) {
    $instance = $old_instance;
    //Fields
    $instance['title'] = strip_tags($new_instance['title']);
    $instance['text'] = strip_tags($new_instance['text']);
    $instance['textarea'] = strip_tags($new_instance['textarea']);
    return $instance;
    /* */
  }

  function widget($args, $instance) {
    extract ($args);
    //The widget Options
    $title = apply_filters('widget_title' , $instance['title']);
    $text = $instance['text'];
    $textarea = $instance['textarea'];
    echo $before_widget;
    //Display Widget
    echo '<div class="widget-text wp_widget_plugin_box">';

    //Check If Title Is Set
    if($title) {
      echo $before_title.$title.$after_title;
    }

    //check if text is set
    if($text) {
      echo '<p class="wp_widget_plugin_text">'.$text.'</p>';
    }

    //check if texrarea is set
    if($textarea) {
      echo '<p class="wp_widget_plugin_textarea">'.$textarea.'</p>';
    }
    echo '</div>';
    echo $after_widget;
  }
}

// register widget
add_action('widgets_init', 'wp_my_plugin');

?>

But when I am trying activate the plugin from dashboard it is showing error like

Warning: call_user_func_array() expects parameter 1 to be a valid callback, function 'wp_my_plugin' not found or invalid function name in /wordpress/wp-includes/plugin.php on line 406 

and the plugin is not activating So can someone kindly tell me how to solve this. Any help will be really appreciable. Thanks

Answer 1

The second parameter for add_action() must be a function or a member of an object. In the second case you have to pass an array ( $object, 'method_name').

To register the widget from within the class, add the following method to your widget class:

/**
 * Tell WP we want to use this widget.
 *
 * @wp-hook widgets_init
 * @return void
 */
public static function register()
{
    register_widget( __CLASS__ );
}

Then change your add_action() call to:

add_action( 'widgets_init', array ( 'wp_my_plugin', 'register' ) );