Overriding current theme files via plugin

Question

I am creating a simple 404 redirect plugin. I want the theme 404.php file to be override when I activate the plugin. There is a 404.php page in the plugin files. File path: plugins/myplugin/files/404.php

How to override 404.php file in theme files with 404.php in plugin folder (When I activate the plugin).

I just created the plugin and activated it. All codes are here:

function my_redicert_plugin() {
global $wpdb;

$table_namex = $wpdb->prefix . 'redirect_p';

$charset_collatex = $wpdb->get_charset_collate();

$sqlx = "CREATE TABLE $table_namex  (
    `id` mediumint(9) NOT NULL AUTO_INCREMENT,
    `mytext` longtext NOT NULL,
    `okbutton` longtext NOT NULL,
    UNIQUE KEY id (id)
    );";

require_once( ABSPATH . 'wp-admin/includes/upgrade.php' );
dbDelta( $sqlx ); 
}


register_activation_hook( __FILE__, 'my_redicert_plugin' );


add_action('admin_menu', 'ds_menux');

function ds_menux() {
    add_menu_page('404 Redirect', '404 Redirect', 'administrator', 'my-redirect-plugin', 'my_r_plugin', 'dashicons-admin-generic'); 
}

(Sorry my English.)

Answer 1

Template logic is primarily controlled by template-loader.php.

The part you are interested in would be get_404_template(), which passes on to generic get_query_template() with number of hooks to override the logic and result.

{$type}_template (so 404_template) filter would probably do it.