如何在Chrome扩展程序中捕获下载进度 [英] How can i capture the download progress in chrome extension

问题描述

我正在创建一个Chrome扩展程序，以监视下载进度.我能够捕获下载开始和下载完成事件，但是不知道如何获得更改的进度?请帮忙. 下面是我的下载监听器

I am creating a chrome extension which moniters the download progress. I am able the capture the download begin and download complete events but have no idea on how to get the changed progress? Please help. Below is my download listener

function AddDownloadListener() {
    //--------------------------------------------------------------------------------------------------------------

    chrome.downloads.onCreated.addListener(DownloadCreated);
    chrome.downloads.onChanged.addListener(DownloadChanged);



    function DownloadCreated(el) {
        console.log("Download Begins");
        console.log(el);
        mobjPortToFoxtrot.postMessage({ message: "Download Begins", element: el });
    }
    //--------------------------------------------------------------------------------------------------------------
        function DownloadChanged(el) {
        if (el.danger === undefined || el.danger == null) {
            console.log(el.state.current);
            mobjPortToFoxtrot.postMessage({ message: el.state.current, element: el });
        }
        else {
            console.log("dangerous content");
            mobjPortToFoxtrot.postMessage({ message: "dangerous content", element: el });
        }
        console.log(el);
    }
}

推荐答案

您不能以基于事件的方式进行操作.

You can't do so in an event-based way.

来自 onChanged文档(重点是我):

From onChanged documentation (emphasis mine):

DownloadItem的任何属性(bytesReceived和estimatedEndTime 除外)发生更改时，都会触发downloadId和包含更改属性的对象.

When any of a DownloadItem's properties except bytesReceived and estimatedEndTime changes, this event fires with the downloadId and an object containing the properties that changed.

这意味着Chrome不会为下载进度触发事件，这是有道理的:这种变化非常频繁，您不希望在每个网络数据包之后触发事件.

This means Chrome will not fire events for the download progress, which kind of makes sense: this changes very frequently, you don't want an event fired after every network packet.

由您自行决定以合理的速率(例如，在进行有效下载时每秒)查询进度，如下所示:

It's up to you to query the progress with a sensible rate (i.e. every second while there is an active download) with something like this:

// Query the proportion of the already downloaded part of the file
// Passes a ratio between 0 and 1 (or -1 if unknown) to the callback
function getProgress(downloadId, callback) {
  chrome.downloads.search({id: downloadId}, function(item) {
    if(item.totalBytes > 0) {
      callback(item.bytesReceived / item.totalBytes);
    } else {
      callback(-1);
    }
  });
}

这篇关于如何在Chrome扩展程序中捕获下载进度的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！