Can't change default thumbnail size - php

Question

I'm making gallery in wordpress and I want to change default thumbnail size but it doesn't work properly. When I set photo as post thumbnail natural size is 150x150 in wordpress media options I changed thumbnail size to 215 143.
in functions I have
add_theme_support( 'post-thumbnails' );
if ( function_exists( 'add_theme_support' ) ) {
add_theme_support( 'post-thumbnails' );
set_post_thumbnail_size( 1240, 1240 );
}
My gallery query:
<ul id="stage">
<?php
// The Query
$the_query = new WP_Query( array( 'post_type' => 'flota', 'orderby' => 'title', 'order' => 'ASC' ) );
// The Loop
while ( $the_query->have_posts() ) : $the_query->the_post();
$thumbnail = wp_get_attachment_image_src( get_post_thumbnail_id ( $the_query->ID ), 'thumbnail' );
$full = wp_get_attachment_image_src( get_post_thumbnail_id ( $the_query->ID ), 'full' );
$cats = wp_get_object_terms( $post->ID, 'flota_category' );
$items = array();
foreach ( $cats as $cat ){
$slug = $cat->slug;
$items[] = $slug;
}
$counter = count($cats);
$i = 0;
?>
<li data-tags="<?php
foreach ( $items as $tag ){
if (++$i === $counter ){
$tags = $tag;
}
else{
$tags = $tag . ', ';
}
echo $tags;
}
?>"><img src="<?php echo $thumbnail[0] ?>" width="215" height="143" style="background:#ffffff;"></li>
<?php
endwhile;
?>
</ul>

Answer 1

In functions.php use:
add_theme_support( 'post-thumbnails' );
add_image_size( 'gallery-thumb', 215, 143 );
Your default posts per page will be 10 which is why you can only see 10 images. Override this by changing your query to:
$the_query = new WP_Query( array( 'post_type' => 'flota', 'orderby' => 'title', 'order' => 'ASC', 'posts_per_page' => -1, ) );
In your query replace $thumbnail and $full with:
$thumbnail = wp_get_attachment_image_src( get_post_thumbnail_id(), 'gallery-thumb' );
$full = wp_get_attachment_image_src( get_post_thumbnail_id(), 'full' );
Then use a plugin like http://wordpress.org/plugins/regenerate-thumbnails/ to regenerate your thumbnails.
In a loop get_post_thumbnail_id doesn't require the ID to be set but if you do decide to set it elsewhere you were looking for $post->ID rather than $the_query->ID. Set $global $post; as well when using it.