Question

我想从网址下载一些文件来刷新我的应用，但我不知道最好的方法是什么。我有这个代码下载一个文件，但是当我下载多个文件时有时会给我一个错误。是否可以在不使用Android Activity的情况下在后台进行下载？谢谢

class DownloadTask extends AsyncTask<String, Integer, String> {

            private Context context;
            private PowerManager.WakeLock mWakeLock;

            public DownloadTask(Context context) {
                this.context = context;
            }

            @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();
                mProgressDialog.show();
            }

            @Override
            protected void onProgressUpdate(Integer... progress) {
                super.onProgressUpdate(progress);
                // if we get here, length is known, now set indeterminate to false
                mProgressDialog.setIndeterminate(false);
                mProgressDialog.setMax(100);
                mProgressDialog.setProgress(progress[0]);
            }

            @Override
            protected void onPostExecute(String result) {
                mWakeLock.release();
                mProgressDialog.dismiss();
                if (result != null)
                    Toast.makeText(context,"Error en la descarga: "+result, Toast.LENGTH_LONG).show();
                else
                    Toast.makeText(context,"Programa actualizado correctamente", Toast.LENGTH_LONG).show();
            }


            @Override
            protected String doInBackground(String... sUrl) {
                InputStream input = null;

                HttpURLConnection connection = null;
                try {
                    URL url = new URL(sUrl[0]);
                    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 "Server returned 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();
                    fOut = openFileOutput("example.json",MODE_PRIVATE);



                    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));
                        fOut.write(data, 0, count);
                    }
                } catch (Exception e) {
                    return e.toString();
                } finally {
                    try {
                        if (fOut != null)
                            fOut.close();
                        if (input != null)
                            input.close();
                    } catch (IOException ignored) {
                    }

                    if (connection != null)
                        connection.disconnect();
                }
                return null;
            }


        }

我用以下方式调用此任务：

downloadTask.execute("myurl");

Answer 1

private class DownloadAsynkTask extends AsyncTask<String, Void, Integer> {

    @Override
    protected void onPreExecute() {
        // progress dialog
    }

    @Override
    protected Integer doInBackground(String... urls) {
        HttpURLConnection connection = null;
        InputStream is = null;

        for (int i=0; i< urls.length; i++) {
            try {
                URL url = new URL(urls[i]);
                connection = (HttpURLConnection) url.openConnection();
                connection.connect();

                if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
                    return connection.getResponseCode();
                } else {
                    is = connection.getInputStream();
                }

                // do something whit url data (add it to list maybe)

                if (connection != null) {
                    connection.disconnect();
                }
                if (is != null) {
                    is.close();
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        return 1;
    }

    @Override
    protected void onPostExecute(Integer result) {
        if (result == 1) {
            // OK
        } else {

        }
    }
}

并将其称为whit String [] urls

new DownloadAsynkTask().execute(urls);

多个文件下载android

1 个答案: