“Next posts” of a category do not call category.php

Question

I try to add a pagination system on my category.php page.

It works for the first page : for example url/category/cat1/. Good number of posts is displayed and I get a "read more" link only when it's needed...

But for the second page : for example url/category/cat1/page/2/. It doesn't load the code from category.php but from index.php !

What am I missing ?

Code from category.php :

<?php

get_header();

    $categories = get_the_category();

    if ( ! empty( $categories ) ) 
    {
        $category = $categories[0]->name;
    }
    $paged = ( get_query_var( 'paged' ) ) ? absint( get_query_var( 'paged' ) ) : 1;

    query_posts( 'category_name='.$category.'&posts_per_page=1&paged='.$paged );

    while (have_posts()) :

        the_post();
        the_title();
        the_excerpt();

        echo'<a href="'.get_permalink().'"> Read more...</a>';

    endwhile;

    ?>

     <div class="navigation">
     <div class="alignleft"><?php previous_posts_link('&laquo; Previous Entries') ?></div>
     <div class="alignright"><?php next_posts_link('Next Entries &raquo;','') ?></div>
     </div>

     <?php

get_footer();

 ?>

Answer 1

First off, don't use query_posts().

The current category will already be available to the category.php template.

To modify the category query and specify the number of posts per page to display, use the pre_get_posts hook and set the value of posts_per_page accordingly. The code below sets posts_per_page to 2. Add this code to you theme's functions.php file:

add_action( 'pre_get_posts', 'wpse_category_posts_per_page' );
function wpse_category_posts_per_page( $query ) {
    if ( is_admin() ) {
        return;
    }

    if ( $query->is_main_query() && $query->is_category() ) {
        $query->set( 'posts_per_page', 2 );
    }
}

Updated category.php template file:

<?php
/**
 * The category template.
 * 
 */
get_header();

if ( have_posts() ) :

    while ( have_posts() ) :
        the_post();
        the_title();
        the_excerpt();
        echo '<a href="' . esc_url( get_permalink() ) . '"> Read more...</a>';
    endwhile;

else :
    echo 'There are no posts in this category.';  
endif;
?>

<div class="navigation">
    <div class="alignleft"><?php previous_posts_link( '&laquo; Previous Entries' ) ?></div>
    <div class="alignright"><?php next_posts_link( 'Next Entries &raquo;','' ) ?></div>
</div>

<?php
get_footer();