ajax working when function is on child theme but not in plugin page

Question

I have an ajax which passes some jQuery variables to PHP function. My function was supposed to be in a class file. But ajax won't work and shows bad request. But if i place php function in my child theme, it works perfectly.

Here is my jQuery AJAX

 $.ajax({
      type: 'POST',
      url: ajaxurl,                        
      data: {
      action: 'thwec_get_element_block_data',
      block_element_list: block_element_list
    },
     success:function(data){
      alert('success');
      console.log(data);
     },
     error: function(){
      alert('error');
     }
    });

And my PHP function.

 public function __construct() {
        add_action('wp_ajax_thwec_get_element_block_data',array($this,'get_element_block_data')); 

        // $this->get_element_block_data();
        // $this->init_constants();
    }

public function get_element_block_data(){
    var_dump("hello");
    exit();
}

Answer 1

And i found the answer. As Jacob Peattie asked the instance of the class was defined but was not called. Although the class file was included , instance was not called. Thank you everyone for your valuable time.