Notice: is_main_query was called incorrectly - php

Question

Was searching for two days what makes problem in my WordPress theme, and using debug I found this error, and that what I have in functions about that error code.
It displays notice on place where section box should be shown.
How can I fix this?
Notice: is_main_query was called incorrectly. In pre_get_posts, use the WP_Query->is_main_query() method,
// Filter to "pre_get_posts" to change query vars
add_action( 'pre_get_posts', 'dp_custom_get_posts' );
function dp_custom_get_posts( $query ) {
if(is_admin())
return;
$orderby = $query->get('orderby');
$order = $query->get('order');
// If no 'orderby' specified, get first sort type from selected sort types
$selected_sort_types = dp_selected_sort_types();
if(is_main_query() && !empty($selected_sort_types) && empty($orderby)) {
$_sort_types = array_keys($selected_sort_types);
$orderby = $_sort_types[0];
$query->set('orderby', $orderby);
}
// Reset query vars based orderby parameter
if($orderby == 'comments') {
$query->set('orderby', 'comment_count');
}
elseif($orderby == 'views') {
$query->set('orderby', 'meta_value_num');
$query->set('meta_key', 'views');
// The arguments for BAW Post Views Count plugin
if(function_exists('baw_pvc_main')) {
global $timings;
$views_timing = $query->get('views_timing') ? $query->get('views_timing') : 'all';
$date = $views_timing == 'all' ? '' : '-'. date( $timings[$views_timing] );
$meta_key = apply_filters( 'baw_count_views_meta_key', '_count-views_' . $views_timing . $date, $views_timing, $date );
$query->set('meta_key', $meta_key);
}
}
elseif($orderby == 'likes') {
$query->set('orderby', 'meta_value_num');
$query->set('meta_key', 'likes');
}
elseif($orderby == 'title' && !$order) {
// If order by title, and no order specified, set "ASC" as default order.
$query->set('order', 'ASC');
}
// Only display posts on search results page
if (is_search() && $query->is_main_query())
$query->set('post_type', 'post');
// Make tax_query support "post-format-standard"
$tax_query = $query->get('tax_query');
if(!empty($tax_query)) {
foreach($tax_query as $index => $single_tax_query) {
if(empty($single_tax_query['terms']))
continue;
$in_post_formats = (array)$single_tax_query['terms'];
if($single_tax_query['taxonomy'] == 'post_format'
&& $single_tax_query['field'] == 'slug'
&& in_array('post-format-standard', $in_post_formats)) {
// Get reverse operator
$reverse_operator = 'IN';
if(empty($single_tax_query['operator']) || $single_tax_query['operator'] == 'IN')
$reverse_operator = 'NOT IN';
elseif($single_tax_query['operator'] == 'AND')
break;
// Get "not in post formats"
$post_formats = get_theme_support('post-formats');
$all_post_formats = array();
if(is_array( $post_formats[0])) {
$all_post_formats = array();
foreach($post_formats[0] as $post_format)
$all_post_formats[] = 'post-format-'.$post_format;
}
$not_in_post_formats = array_diff($all_post_formats, $in_post_formats);
// Reset post_format in tax_query
$query->query_vars['tax_query'][$index] = array(
'taxonomy' => 'post_format',
'field' => 'slug',
'terms' => $not_in_post_formats,
'operator' => $reverse_operator
);
}
}
}
return $query;
}
This is the code of an section box, or at least part of it, I'm not sure what I'm doing anymore:
function dp_section_box($args = array()) {
$defaults = array(
'post_type' => 'post',
'cat' => '',
'taxonomies' => array(),
'view' => 'grid-small',
'title' => '',
'link' => '',
'post__in' => '',
'posts_per_page' => '',
'hide_if_empty' => false
);
$args = wp_parse_args($args, $defaults);
extract($args);
$posts_per_page = absint($posts_per_page);
// Set default posts number if no specified
if(empty($posts_per_page)) {
if($view == 'grid-mini')
$posts_per_page = 8;
elseif($view == 'grid-small')
$posts_per_page = 6;
elseif($view == 'grid-medium')
$posts_per_page = 4;
elseif($view == 'list-small')
$posts_per_page = 3;
elseif($view == 'list-medium')
$posts_per_page = 2;
elseif($view == 'list-large')
$posts_per_page = 1;
}
$args['posts_per_page'] = $posts_per_page;
$args = dp_parse_query_args($args);
$query = new WP_Query($args);
// Output nothing if there is no posts
if(!$query->have_posts() && $hide_if_empty)
return;
// Output content before section
if(!empty($before))
echo '<div class="section-box section-before rich-content">'. do_shortcode(wp_kses_stripslashes($before)).'</div><!-- end .section-box -->';
// Section box begin
echo '<div class="section-box">';
global $section_view;
$section_view = $view;
// Get term name as title
$term = '';
$cat = '';
if(!empty($taxonomies['category']))
$cat = $taxonomies['category'];
if($cat)
$term = get_term($cat, 'category');
if(empty($title) && $term)
$title = $term->name;
if(empty($link) && $term)
$link = get_term_link($term, 'category');
$title = '<span class="name">'.$title.'</span>';
// Add link to title and more
$more = '';
if($link) {
$title = '<a class="name-link" href="'.$link.'">'.$title.'</a>';
$more = '<a class="more-link" href="'.$link.'"><span>'.__('More', 'dp').' <i class="mini-arrow-right"></i></span></a>';
}
// Output section header
echo '<div class="section-header"><h2 class="section-title">'.$title.'</h2>'.$more.'</div>';
// Output section content
echo '<div class="section-content '.$view.'"><div class="nag cf">';
while ($query->have_posts()) : $query->the_post();
get_template_part('item-video');
endwhile;
wp_reset_postdata();
echo '</div></div><!-- end .section-content -->';

Answer 1

the solution is given in your error itself "use the WP_Query->is_main_query() method"-
try this -
if($query->is_main_query() && !empty($selected_sort_types) && empty($orderby)) {
$_sort_types = array_keys($selected_sort_types);
$orderby = $_sort_types[0];
$query->set('orderby', $orderby);
}
instead of this -
if(is_main_query() && !empty($selected_sort_types) && empty($orderby)) {
$_sort_types = array_keys($selected_sort_types);
$orderby = $_sort_types[0];
$query->set('orderby', $orderby);
}