PHP 问题：如何把上传文件这个功能改为选择性的？目前是必须的，谢谢

我自己加了个很简单的判断，但是不对，文件上传不了了，也没错误提示
在线等，谢谢！

code:
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<?php
include ('../header.php');
include ('../secure_page.php');
include ('../php/phpClass/data_class.php');

$userID=$_SESSION['user_id'];
$user=$_SESSION['username'];

$dest_dir="../media/$user/".date(Ymd);

if( !is_dir($dest_dir) || !is_writeable($dest_dir) )
{
if(!mkdir($dest_dir, 0777, true))
die("The expected directory ".$dest_dir." encountered errors");
}

$type=array("png","jpg","jpeg");

$upfile=$_FILES['file'];

if($upfile != NULL)
{

function fileext($filename)
{
return substr(strrchr($filename, '.'), 1);
}

if( !in_array( strtolower( fileext($upfile['name'] ) ),$type) )
{
$text=implode(",",$type);
echo "Sorry, you cannot upload this file type: ",$text;
}
else
{
$dest=$dest_dir.'/'.date("His")."_".$upfile['name'];

$state=move_uploaded_file($upfile['tmp_name'],$dest);

if ($state)
{
print("File Uploaded. Thanks for your contribution!");
}
else
{
switch($upfile['error'])
{
case 1 : die("File size is larger than php.ini: upload_max_filesize");
case 2 : die("File is too large");
case 3 : die("Only part of file has been uploaded");
case 4 : die("No file has been uploaded");
case 5 : die("Cannot find the expected directory");
case 6 : die("File cannot be written");
}
}
}
}
else
{
print("Thanks for your contribution!");
}

$aname = $_POST['aname'];
$atime = $_POST['atime'];
$adate = $_POST['adate'];
$latitude = $_POST['latitude'];
$longitude = $_POST['longitude'];
$agchoice = $_POST['agchoice'];
$age = $_POST['age'];
$aschoice = $_POST['aschoice'];
$adescription = $_POST['adescription'];

$dataClass = new Data();
$data = array($aname,$atime,$adate,$latitude,$longitude,$agchoice,$aschoice,$adescription,$age,$dest);

$h = $dataClass->add_sighting($data, $userID);

?>
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