javascript - 使用 XHR2/AJAX 显示下载文件的进度条

Question

我正在尝试使用 Ajax 下载文件并显示自定义下载进度条。

问题是我不明白该怎么做。我编写了代码来记录进度，但不知道如何启动下载。

注意:文件的类型不同。

提前致谢。

JS

// Downloading of files
filelist.on('click', '.download_link', function(e){
    e.preventDefault();
    var id = $(this).data('id');
    $(this).parent().addClass("download_start");

    $.ajax({
        xhr: function () {
            var xhr = new window.XMLHttpRequest();
            // Handle Download Progress
            xhr.addEventListener("progress", function (evt) {
                if(evt.lengthComputable) {
                    var percentComplete = evt.loaded / evt.total;
                    console.log(percentComplete);
                }
            }, false);
            return xhr;
        },
        complete: function () {
            console.log("Request finished");
        }
    })
});

HTML 和 PHP

    <li>
    <div class="f_icon"><img src="' . $ico_path . '"></div>
    <div class="left_wing">
       <div class="progressbar"></div>
       <a class="download_link" href="#" id="'.$file_id.'"><div class="f_name">' . $full_file_name . '</div></a>
       <div class="f_time_size">' . date("M d, Y", $file_upload_time) . '&nbsp; &#149; &nbsp;' . human_filesize($file_size) . '</div>
    </div>

    <div class="right_wing">
       <div class="f_delete">
       <a class="btn btn-danger" href="#" aria-label="Delete" data-id="'.$file_id.'" data-filename="'.$full_file_name.'"><i class="fa fa-trash-o fa-lg" aria-hidden="true" title="Delete this?"></i>
       </a>
    </div>
   </div>
    </li>

Answer 1

如果您想向用户显示下载过程的进度条 - 您必须在 xmlhttprequest 中进行下载。这里的问题之一是，如果您的文件很大 - 在浏览器将它们写入磁盘之前，它们将被保存在浏览器的内存中(使用常规下载文件时会直接保存到磁盘，这在大文件上节省了大量内存)。

另一个需要注意的重要事项 - 为了使 lengthComputable 为真 - 您的服务器必须发送包含文件大小的 Content-Length header 。

这是javascript代码:

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="a1" data-filename="filename.xml">Click to download</div>
<script>
$('#a1').click(function() {
    var that = this;
    var page_url = 'download.php';

    var req = new XMLHttpRequest();
    req.open("POST", page_url, true);
    req.addEventListener("progress", function (evt) {
        if(evt.lengthComputable) {
            var percentComplete = evt.loaded / evt.total;
            console.log(percentComplete);
        }
    }, false);

    req.responseType = "blob";
    req.onreadystatechange = function () {
        if (req.readyState === 4 && req.status === 200) {
            var filename = $(that).data('filename');
            if (typeof window.chrome !== 'undefined') {
                // Chrome version
                var link = document.createElement('a');
                link.href = window.URL.createObjectURL(req.response);
                link.download = filename;
                link.click();
            } else if (typeof window.navigator.msSaveBlob !== 'undefined') {
                // IE version
                var blob = new Blob([req.response], { type: 'application/force-download' });
                window.navigator.msSaveBlob(blob, filename);
            } else {
                // Firefox version
                var file = new File([req.response], filename, { type: 'application/force-download' });
                window.open(URL.createObjectURL(file));
            }
        }
    };
    req.send();
});
</script>

这里是您可以使用的 php 代码示例:

<?php
$filename = "some-big-file";
$filesize = filesize($filename);

header("Content-Transfer-Encoding: Binary");
header("Content-Length:". $filesize);
header("Content-Disposition: attachment");

$handle = fopen($filename, "rb");
if (FALSE === $handle) {
    exit("Failed to open stream to URL");
}

while (!feof($handle)) {
    echo fread($handle, 1024*1024*10);
    sleep(3);
}

fclose($handle);

Note that I added a sleep to simulate a slow connection for testing on localhost.
You should remove this on production :)