更新到 Codeigniter 3.x 后，为什么在 ajax 调用期间出现 json 解析错误？

Question

I am updating my Codeigniter framework from 2.2.6 to 3.0.6. It has broken the existing code that worked before. Specifically, I am getting the error "SyntaxError: JSON.parse: unexpected character at line 2 column 1 of the JSON data" inside the browser console. I have tried to look and see if this is a known issue when updating, but I have not seen anyone else experiencing this.

Here is the javascript that I am using:

    $('#addServiceItem').on('change', function() {
        var serviceID = $(this).val();
        $.ajax({
            url: '/ajax/get_service_details/' + serviceID,
        }).done(function(data) {
            if (data.status == 'success') {
                addServiceItem(data.service);
            } else {
                alert(data.message);
            }
        });
    });

Also, here is the function that is being called in the ajax url:

public function get_service_details($serviceID = 0)
    {
        if (!$this->input->is_ajax_request()) {
            exit('No direct script access allowed');
        }

        if ($serviceID == 0) {
            header('Content-type: application/json');
            echo json_encode(array(
                'status' => 'error',
                'service' => null,
                'message' => 'We could not find the service.'
            ));
        }

        $service = $this->services_model->get_service_details($serviceID);

        header('Content-type: application/json');
        echo json_encode(array(
            'status' => 'success',
            'service' => $service,
            'message' => ''
        ));
    }

As stated above, this code worked in the previous version of Codeigniter. As far as I can tell there is an issue with the Ajax call returning a value. In the javascript variable data stays undefined. I assume that there is a syntax standard that has changed.

Answer 1

If your $serviceID == 0 , then you get error Headers already sent because inside IF you output content and do not terminate code, and outside of IF you again try to set header.

Change your code to this one:

public function get_service_details($serviceID = 0)
{
    if (!$this->input->is_ajax_request()) {
        exit('No direct script access allowed');
    }

    if ($serviceID == 0) {
        header('Content-type: application/json');
        echo json_encode(array(
            'status' => 'error',
            'service' => null,
            'message' => 'We could not find the service.'
        ));

        // Terminate function execution
        return;
    }

    $service = $this->services_model->get_service_details($serviceID);

    header('Content-type: application/json');
    echo json_encode(array(
        'status' => 'success',
        'service' => $service,
        'message' => ''
    ));
}