Dynamically assign same page template to child page as parent

Question

How to assign parent page template to its child pages dynamically?

Answer 1

Paste following code to your theme's functions.php:

add_action('save_post','changeTemplateOnSave');
function changeTemplateOnSave(){
    global $post;
    $curr_tmp = get_post_meta($post->ID, '_wp_page_template', true);
    $parent_tmp = get_post_meta($post->post_parent, '_wp_page_template', true);
    if($post->post_parent)
        update_post_meta($post->ID,'_wp_page_template',$parent_tmp,$curr_tmp);
}

This will force WordPress to change page template to it's parent template on post save.
Not tested but should work.

Answer 2

A little correction to the Max Yudin's solution:

add_action('save_post','changeTemplateOnSave');
function changeTemplateOnSave(){
    global $post;
    $curr_tmp = get_post_meta($post->ID, '_wp_page_template', true);
    if($post->post_parent){
        $parent_tmp = get_post_meta($post->post_parent, '_wp_page_template', true);
        update_post_meta($post->ID,'_wp_page_template',$parent_tmp,$curr_tmp);
    }
}

Answer 3

One further little correction if you care about php warnings in the background.

When creating a new post/page the folllow notice was being output

Notice: Trying to get property of non-object error

Fixed this by making sure $post exists or and is not empty.

add_action('save_post','changeTemplateOnSave');

if ( ! function_exists( 'changeTemplateOnSave' ) ) {

    function changeTemplateOnSave() {

        global $post;

        if ($post) {

            $curr_tmp = get_post_meta( $post->ID, '_wp_page_template', true );

            if ( $post->post_parent ) {

                $parent_tmp = get_post_meta( $post->post_parent, '_wp_page_template', true );

                update_post_meta( $post->ID, '_wp_page_template', $parent_tmp, $curr_tmp );
            }
        }
    }
}