Export CSV File in Wordpress - php

Question

there is a button on my settings that once clicked it will prompt to download a csv file. Here is the code.
<?php
/** Step 2 (from text above). */
add_action( 'admin_menu', 'my_plugin_menu' );
/** Step 1. */
function my_plugin_menu() {
add_options_page( 'Members Log Data',
'Members Log',
'manage_options',
'sj-member-option',
'members_option' );
}
/** Step 3. */
function members_option() {
if ( !current_user_can( 'manage_options' ) )
{
wp_die( __( 'You do not have sufficient permissions to access this page.' ) );
}
$name = "member-log-".date('Y-m-d');
$list[] = array('username','no of favorites');
header('Content-Type: text/csv; charset=utf-8');
header('Content-Disposition: attachment; filename=' . $name);
$op = fopen('php://output','w');
foreach($list as $row)
{
fputcsv($op,$row);
}
fclose($op);
/*
echo '<div class="wrap">';
echo '<p>Here is where the form would go if I actually had options.</p>';
echo '</div>';
*/
}
I am getting can not modify session header.
I would like to ask how to do this in WP as I am familiar outside of it.

Answer 1

You're trying to send a header command too late, hence the error. Use the hook load-(your_page) for this kind of output.
function my_plugin_menu() {
$page = add_options_page( 'Members Log Data',
'Members Log',
'manage_options',
'sj-member-option',
'members_option' );
add_action( "load-$page", 'do_export' );
}
In the members_option function callback add a <form> with a submit button and in the new do_export function you'll put the export actions. Something like bellow, note that I'm not checking for the nonce, but for security best practices you should do it instead of checking for $_POST['submit'].
function members_option() {
if ( !current_user_can( 'manage_options' ) )
{
wp_die( __( 'You do not have sufficient permissions to access this page.' ) );
}
?>
<form method='post' >
<p class="submit">
<?php wp_nonce_field('my-import'); ?>
<input type='submit' name='submit' value='Restore'/>
</p>
</form>
<?php
}
function do_export() {
if( isset( $_POST['submit'] ) && 'Restore' == $_POST['submit'] )
{
$name = "member-log-".date('Y-m-d');
$list[] = array('username','no of favorites');
header('Content-Type: text/csv; charset=utf-8');
header('Content-Disposition: attachment; filename=' . $name);
$op = fopen('php://output','w');
foreach($list as $row)
{
fputcsv($op,$row);
}
fclose($op);
}
}
In my tests, the export result was an HTML file with the full contents of the page plus the 'username','no of favorites' that you defined, but this is a matter for another question/research.