使用jQuery和CodeIgniter将img文件动态发送到服务器

我正在努力使其在提交图像时，使用CodeIgniter将图像保存到服务器，然后通过jquery在前端显示。

HTML:

<form id="set" method="post" action="<?php echo $base_url; ?>schedule/sample" enctype="multipart/form-data">
    <input type="file" name="file" id="file">
    <img id="result" src="" width="50" height="50" alt="sample" style="display:hidden;"/>
</form>

JS:

$("#file").change(function() {
    var file = this.files[0];
    var full = base_url +'public/img/'+ file.name;
    $.ajax({  
        type:'POST',  
        url:base_url +'schedule/sample',  
        data:'file='+ file,
        success: function() {
           $('#result').attr('href', full);
           $('#result').fadeIn('fast');
        }
    });
});

PHP（调度控制器）:

 public function __construct() {       
        parent:: __construct();
        $base_url = $this->config->base_url();
        $this->load->database();
        $this->load->model('paypal_model');
        $config['upload_path'] = 'public/img/';
        $config['allowed_types'] = 'jpg|jpeg';
        $config['max_size'] = '1000';
        $config['max_width'] = '1024';
        $config['max_height'] = '768';
        $this->load->helper(array('form', 'url'));
        $this->load->library('file');
        $this->load->library('upload', $config);
        $this->load->library('session');
}
    public function sample() {  
        $image = $this->input->post('file');
        $base_url = $this->config->base_url();
        if(!$this->upload->do_upload('file')) {    
            $error = array('error' => $this->upload->display_errors());
            echo 'not uploaded';
        } else {
            $pic = $this->upload->data();
            print_r($pic);
            write_file('public/img/'.$fb_id.'.jpg', $img_data);
            $img = $pic['image_width'];
        }
    }