【发布时间】：2015-12-30 01:26:59
【问题描述】：
我的应用是一个媒体播放器，它通过从 Internet 下载适当的文件来播放媒体。我正在使用AsyncTask 来执行此操作，但是当需要下载多个文件时执行任务需要更长的时间，这会导致媒体播放器延迟。
所需的行为是在下载文件后开始播放文件，同时继续下载任何其他文件。
我的代码如下：
public class DownloadTask extends AsyncTask<String, Integer, String> {
private Context context;
private PowerManager.WakeLock mWakeLock;
private String folder;
private ProgressDialog mProgressDialog;
private int noOfURLs;
private int noUrlLoad;
public DownloadTask(Context context, String folder, ProgressDialog mProgressDialog) {
this.context = context;
this.folder = folder;
}
@Override
protected String doInBackground(String... sUrl) {
InputStream input = null;
OutputStream output = null;
HttpURLConnection connection = null;
try {
noOfURLs = sUrl.length;
for (int i = 0; i < sUrl.length; i++) {
URL url = new URL(sUrl[i]);
connection = (HttpURLConnection) url.openConnection();
connection.connect();
// expect HTTP 200 OK, so we don't mistakenly save error report
// instead of the file
if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
return "Máy chủ trả về HTTP " + connection.getResponseCode()
+ " " + connection.getResponseMessage();
}
// this will be useful to display download percentage
// might be -1: server did not report the length
int fileLength = connection.getContentLength();
// download the file
input = connection.getInputStream();
output = new FileOutputStream(Environment.getExternalStorageDirectory() + "/" + folder + "/File" + (i + 1) + "." + sUrl[i].charAt(sUrl[i].length() - 3) + sUrl[i].charAt(sUrl[i].length() - 2) + sUrl[i].charAt(sUrl[i].length() - 1));
byte data[] = new byte[4096];
long total = 0;
int count;
while ((count = input.read(data)) != -1) {
// allow canceling with back button
if (isCancelled()) {
input.close();
return null;
}
total += count;
// publishing the progress....
if (fileLength > 0) // only if total length is known
publishProgress((int) (total * 100 / fileLength));
output.write(data, 0, count);
}
noUrlLoad++;
} catch (Exception e) {
return e.toString();
} finally {
try {
if (output != null)
output.close();
if (input != null)
input.close();
} catch (IOException ignored) {
}
if (connection != null)
connection.disconnect();
}
return null;
}
@Override
protected void onPreExecute() {
super.onPreExecute();
// take CPU lock to prevent CPU from going off if the user
// presses the power button during download
PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE);
mWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK,
getClass().getName());
mWakeLock.acquire();
}
@Override
protected void onProgressUpdate(Integer... progress) {
super.onProgressUpdate(progress);
// if we get here, length is known, now set indeterminate to false
}
@Override
protected void onPostExecute(String result) {
mWakeLock.release();
mProgressDialog.dismiss();
if (result != null)
Toast.makeText(context, context.getString(R.string.error) + result, Toast.LENGTH_LONG).show();
}
}
【问题讨论】：
标签： android file download android-asynctask