android webview file download/php provides - php

Question

Provides file downloads with PHP.
It works fine on the web, but it does not work properly in the app.
What is the reason why the header of the file is normally displayed but the file is not downloaded?
android webview download
DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));
request.setMimeType(mimetype);
request.addRequestHeader("User-Agent", userAgent);
request.setDescription("Downloading file");
request.setTitle(URLUtil.guessFileName(url,contentDisposition,mimetype));
request.allowScanningByMediaScanner();
request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, URLUtil.guessFileName(url,contentDisposition,mimetype));
DownloadManager dm = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
headers
header('Content-Type: ' . $this->mimetype);
header('Content-Disposition: attachment; filename="' . $this->dl_filename . '"');
header("Content-Transfer-Encoding: binary");
header('Accept-Ranges: bytes');
/* The three lines below basically make the
download non-cacheable */
header("Cache-control: private");
header('Pragma: private');
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
// multipart-download and download resuming support
if(isset($_SERVER['HTTP_RANGE']) && !$this->force_single){
list($a, $range) = explode("=", $_SERVER['HTTP_RANGE'], 2);
list($range) = explode(",", $range, 2);
list($range, $range_end) = explode("-", $range);
$range = intval($range);
if(!$range_end){
$range_end = $size - 1;
}else{
$range_end = intval($range_end);
}
$new_length = $range_end - $range + 1;
header('HTTP/1.1 206 Partial Content');
header('Content-Length: ' . $new_length);
header('Content-Range: bytes ' . $range . '-' . $range_end . '/' . $size);
//set the offset range
$this->mt_range = $range;
}else{
$new_length = $size;
header("Content-Length: " . $size);
}
download file
if($file = fopen($filename, 'r')){
if(isset($_SERVER['HTTP_RANGE']) && !$this->force_single){
fseek($file, $this->mt_range);
}
//write the data out to the browser
while(!feof($file) && !connection_aborted() && $bytes_send < $block_size){
$buffer = fread($file, $chunksize);
echo $buffer;
flush();
$bytes_send += strlen($buffer);
}
fclose($file);
}