如何在Android中通过onResume（）恢复下载？

Question

My application has a "start download" and a "pause" button. Once I start the download through "Start Download" button my download starts and stop upon clicking "pause" now when I press back or home button the onPause() function works as intended it pauses my download and when I open the app again and click start it resumes from that progress,

what I want is that upon switching back(not the first time load of app) to the application once I have pressed back or home I want the download to resume automatically by onResume without clicking start button again. Right now in below code my download automatically starts without doing anything which is due to my onResume(), is it possible that I can resume with onResume but not start the download automatically upon first time loading of the app thorugh it? I know the below code is not as efficient as it could have been. Apologies for that.

Again, I want my onResume to only resume my previously downloaded file not start the download unless download was once initiated through the button.

public class MainActivity extends Activity implements OnClickListener{
    String url = "http://upload.wikimedia.org/wikipedia/commons/1/11/HUP_10MB_1946_obverse.jpg";
    boolean mStopped=false;

     private ProgressBar progressBar2;
     private String filepath = "MyFileStorage";
     private File directory;
     private TextView finished;
        @Override
        protected void onPause() {
         super.onPause();
         mStopped=true;
        }
        @Override
        protected void onResume() {
         super.onResume();
         mStopped=false;
         grabURL(url);
        }

        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);

            ContextWrapper contextWrapper = new ContextWrapper(getApplicationContext());
            directory = contextWrapper.getDir(filepath, Context.MODE_PRIVATE);

            progressBar2 = (ProgressBar) findViewById(R.id.progressBar2);
            progressBar2.setVisibility(View.GONE);
            finished = (TextView) findViewById(R.id.textView1);
            finished.setVisibility(View.GONE);


      Button stop = (Button) findViewById(R.id.stop);
      stop.setOnClickListener(this);
      Button download = (Button) findViewById(R.id.download);
      download.setOnClickListener(this);

        }

        public void onClick(View v) {

      switch (v.getId()) {

      case R.id.stop:
            mStopped=true;
       break;

      case R.id.download:
          mStopped=false;
       grabURL(url); 
       break; 



      }
     }

        public void grabURL(String url) {
      new GrabURL().execute(url);
     }

     private class GrabURL extends AsyncTask<String, Integer, String> {


      protected void onPreExecute() {
       progressBar2.setVisibility(View.VISIBLE);
             progressBar2.setProgress(0);
             finished.setVisibility(View.GONE);

         }

      protected String doInBackground(String... urls) {



       String filename = "MySampleFile.png";
       File myFile = new File(directory , filename);

       try {
                 URL url = new URL(urls[0]);
                 URLConnection connection = url.openConnection();
                 if (myFile.exists())
                 {
                     connection.setAllowUserInteraction(true);
                     connection.setRequestProperty("Range", "bytes=" + myFile.length() + "-");
                 }
                 connection.connect();
                 int fileLength = connection.getContentLength(); 
                 fileLength += myFile.length(); 
                 InputStream is = new BufferedInputStream(connection.getInputStream());
                 RandomAccessFile os = new RandomAccessFile(myFile, "rw");


                 os.seek(myFile.length());

                 byte data[] = new byte[1024];
                 int count;
                 int __progress = 0;
                 while ((count = is.read(data)) != -1 && __progress != 100) {
                     if (mStopped) {
                           throw new IOException();
                     }
                     else{
                     __progress = (int) ((myFile.length() * 100) / fileLength);
                     publishProgress((int) (myFile.length() * 100 / fileLength));
                     os.write(data, 0, count);}
                 }
                 os.close();
                 is.close();

             } catch (Exception e) {
              e.printStackTrace();
             }

       return filename;

      }

      protected void onProgressUpdate(Integer... progress) {
       finished.setVisibility(View.VISIBLE);
       finished.setText(String.valueOf(progress[0]) + "%");
       progressBar2.setProgress(progress[0]);
         }

      protected void onCancelled() {
       Toast toast = Toast.makeText(getBaseContext(), 
         "Error connecting to Server", Toast.LENGTH_LONG);
       toast.setGravity(Gravity.TOP, 25, 400);
       toast.show();

      }

      protected void onPostExecute(String filename) {
              progressBar2.setProgress(100);
              finished.setVisibility(View.VISIBLE);
              finished.setText("Download in progress..");
              File myFile = new File(directory , filename);
              ImageView myImage = (ImageView) findViewById(R.id.imageView1);
              myImage.setImageBitmap(BitmapFactory.decodeFile(myFile.getAbsolutePath()));

      }

     }

        @Override
        public boolean onCreateOptionsMenu(Menu menu) {
            getMenuInflater().inflate(R.menu.activity_main, menu);
            return true;
        }
    }

Answer 1

You seem to already have most of the code in place for the functionality. In onResume you can call your ASyncTask and it should start download if the file exists (paused download in onPause(), file exists). I have written similar code, you can find it here: https://github.com/hiemanshu/ContentDownloader/blob/master/src/com/example/contentdownloader/MainActivity.java In my code you can find that instead of using onPause and onResume, I just have a wakelock for that period of time.