php - Fatal error: Class 'WP_Customize_Control' not found - WordPress -

im building own wordperss theme , when starting on wordpress customizer theme options have come in little bit of trouble.

basically im trying create textarea , have read need create extended class , call under add_control function of wordpress.

i have tried , works in customizer mode enter other part of site error:

fatal error: class 'wp_customize_control' not found

as works 100% within customizer it's self other page including admin message.

here class:

class ublxlportfolio_textarea extends wp_customize_control {     public $type = 'textarea';      public function render_content() {         ?>         <label>         <span class="customize-control-title"><?php echo esc_html( $this->label ); ?></span>         <textarea rows="5" style="width:100%;" <?php $this->link(); ?>><?php echo esc_textarea( $this->value() ); ?></textarea>         </label>         <?php     } } 

do need wrap in conditional tag? if be??

am doing wrong?

to clarify @robert's correct answer:

class wp_customize_control loaded when theme customizer acutally used. so, need define class within function bind 'customize_register' action.

example:

add_action( 'customize_register', 'my_customize_register' );  function my_customize_register($wp_customize) {    //class definition must within my_customie_register function   class ublxlportfolio_textarea extends wp_customize_control { ... }    //other stuff }