"Undefined index" error when saving empty array with checkboxes

Question

In my plugin settings page, I have a list of checkboxes that store the value into an array. While the it works as expected, whenever I uncheck all of the checkboxes and save those changes I get the following error:

Notice: Undefined index: remove_field in ...\settings-profile.php on line 19

Below is the code in question:

if ( isset( $_POST['dsbl_options'] ) && !empty( $_POST['dsbl_options'] ) ) {
    update_option( 'dsbl_remove', $_POST['remove_field'] ); // (Line 19)
}

The rest of the source code can be found here: GitHub

From doing research online for a similar error, I see that the recommendation is to wrap $_POST['remove_field'] with an isset. However, this does not store the values form the checkboxes in the plugin settings.

As mentioned above, this error shows up only when all of the checkboxes are unchecked and saved. It looks like there is an issue when saving an empty value in the array. Although the plugin settings works as expected, I'd like to fix this.

Answer 1

I'm not seeing the original snippet from before so I'm not sure of the context anymore. The undefined index notice you are getting is telling you that $_POST['remove_fiel‌​d'] does not exist. If no checkbox in your array was set, the $_POST array will not have an index for 'remove_field', and you'll see the error.

To prevent this from happening, ensure it exists:

if ( isset( $_POST['remove_field'] ) ) {
    // do stuff with the values
}

When in an OO context the more frequent solution is to bail out if no value exists so you would reverse your condition:

if ( !isset( $_POST['remove_field'] ) ) {
    return;
}

Answer 2

As mentioned here (thanks to bcworkz), I was able to fix the issue by inserting NULL if all of the checkboxes are unchecked:

if ( isset( $_POST['dsbl_options'] ) && !empty( $_POST['dsbl_options'] ) ) {
    if ( array_key_exists('remove_field', $_POST )) {
        update_option( 'dsbl_remove', $_POST['remove_field'] );
    }
    else { // When all options are unchecked, set array to null
        update_option( 'dsbl_remove', NULL );
    }
}