无法传输pdf：标头已经在托管后发送了codeigniter

Question

有人能帮我吗？我在codeigniter中使用dompdf，我正在尝试所有解决方案，然后没有人可以解决我的问题。当使用localhost没有问题，托管后有一个错误Unable to stream pdf: headers already sent请帮助我，我还在学习。

这是我的控制器Laporanpdf.php

`<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
class Laporanpdf extends CI_Controller {
public function __construct() {
parent::__construct();
$this->load->model('model_laporan');
$this->load->library('dompdf_gen');
}
public function index(){
        $data['title'] = 'Cetak Laporan Kinerja'; //judul title
        if($this->session->userdata('level')=='1-Admin'){
        $data['pengguna'] = $this->model_laporan->pengguna_admin(); //query model        
        $data['kinerja'] = $this->model_laporan->kinerja_admin(); //query model
        $data['awal'] = strtotime($this->input->get('awal'));
        $data['jbtn_atasn'] = $this->input->get('jbtn_atasn');
        $data['nip_atsn'] = $this->input->get('nipeg');
        $data['pangkat_atsn'] = $this->input->get('pngkat');
    $data['gol_atsn'] = $this->input->get('gol');
}else{
    $data['pengguna'] = $this->model_laporan->pengguna_else(); //query model        
    $data['kinerja'] = $this->model_laporan->kinerja_else(); //query model
    $data['jbtn_atasn'] = $this->input->get('jbtn_atasn');
    $data['nip_atsn'] = $this->input->get('nipeg');
    $data['pangkat_atsn'] = $this->input->get('pngkat');
    $data['gol_atsn'] = $this->input->get('gol');
}
if($this->session->userdata('level')=='1-Admin'){
    if ($this->model_laporan->kinerja_admin()==null){
//pesan error
        echo "<script>alert('Kinerja dengan tanggal tersebut tidak tersedia. Silahkan masukan tanggal yang sesuai.');
        window.location='/kinerja/index.php/kinerja';
        </script>";
        exit();
    } else {
        $this->load->view('v_cetak', $data, TRUE);
    }
}else{
    if ($this->model_laporan->kinerja_else()==null){
//pesan error
        echo "<script>alert('Kinerja dengan tanggal tersebut tidak tersedia. Silahkan masukan tanggal yang sesuai.');
        window.location='/kinerja/index.php/kinerja';
        </script>";
        exit();
    } else {
        $this->load->view('v_cetak', $data, TRUE);
    }
}
    $paper_size  = 'A4'; //paper size
    $orientation = 'potrait'; //tipe format kertas
    $html = $this->output->get_output();
    $this->dompdf->set_paper($paper_size, $orientation);
    //Convert to PDF
    $this->dompdf->load_html($html);
    $this->dompdf->render();
    $this->dompdf->stream("laporan.pdf", array('Attachment'=>0)); //preview pada browser
}
}`

这是我放入应用程序/库的Dompdf_gen.php

`<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
class Dompdf_gen {
    public function __construct() {
        require_once APPPATH.'third_party/dompdf/dompdf_config.inc.php'; // @version 0.5.1.htischer.20090507
        $pdf = new DOMPDF();
    $CI =& get_instance();
    $CI->dompdf = $pdf;
}
}`