Question

I’m not really sure what goes wrong with my code or structure. I wanted to use AsyncTask to download images and display out the progress bar at the mean time. But I tried out a few different way of doing it. It still failed and no idea what’s wrong with it. My structure flow is

ContentID is a string array that stores the content ID of the Images.

Primary Issue: It managed to download images from the url and store into the phone, but the downloaded images are all the same image. It should be different images, it’s not what I expected.

Secondary Issue: The progress bar pop up while the application downloading images, but the progress bar did not update it’s progress. It just remains 0% and dismissed after the download completed.

I wanted to know what causes primary and secodary issue as i mentioned. Please leave a comment or answer if you might know what’s wrong with my code. Any help will be appreciated.

if(isSyncSuccess){

     SetConstant.IMAGE_EXIST = 1;
     pDialog = new ProgressDialog(GalleryScreen.this);
     pDialog.setMessage("Downloading file. Please wait...");
     pDialog.setIndeterminate(false);
     pDialog.setProgress(0);
     pDialog.setMax(contentId.length);
     pDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
     pDialog.setCancelable(true);


     if (contentId.length>0){
     Log.i(TAG, "contentid.length:" +contentId.length);
         for (int i=0;i<contentId.length;i++){
             if(helper.databaseChecking(useremail, contentId[i])){
                 contentdownload = i;
                 SetConstant.CONTENT_ID = contentId[i]; 

                 String URL = SetConstant.URL_DOWNLOAD_CONTENT+contentId[i];

                 DownloadFile downloadFile = new DownloadFile();
                 downloadFile.execute(URL);


                 }



    private class DownloadFile extends AsyncTask<String, Integer, String>{
    @Override
    protected String doInBackground(String... sUrl){
                Bitmap bm;
                InputStream in;

        try{

            in = new java.net.URL(sUrl[0]).openStream();
            bm = BitmapFactory.decodeStream(new PatchInputStream(in));
            File storage = new File(Environment.getExternalStorageDirectory() + File.separator + "/Image/");
            Log.i(TAG,"storage:" +storage);
            Log.i(TAG,"storage:" +storage.getAbsolutePath());
            if(!storage.exists()){
                storage.mkdirs();

            }
                String FileName = "/"+SetConstant.CONTENT_ID+".jpg"; 
                FileOutputStream fos = new FileOutputStream(storage + FileName);
                bm.compress(Bitmap.CompressFormat.JPEG, 85, fos);

                String filepath = storage + FileName;
                File filecheck = new File (filepath);
                long fileSize = filecheck.length();
                fos.flush();
                fos.close();

                Log.i(TAG, "bm:" +bm);
                Log.i(TAG, "fos:" +fos);
                Log.i(TAG, "filesize:" +fileSize);
                Log.i(TAG, "filepath:" +filepath);


        }
        catch(IOException e1){
                e1.printStackTrace();
                }   

        return null;
    }

    @Override
    protected void onPreExecute(){
        super.onPreExecute();
        pDialog.show();
    }

    @Override
    protected void onProgressUpdate(Integer... progress){
        super.onProgressUpdate(progress);
        pDialog.setProgress(progress[0]);
    }

    protected void onPostExecute(String result){
        super.onPostExecute(result);
        pDialog.dismiss();
    }
}

Edit

Now the application able to download images according and the progress bar is working as well! But I got another issue is how to return error message when the application failed to complete the download. Currently when the application failed to download it will crash. I believed that I should not run it inside the doInBackground side. But where else can I do the checking? Any idea how to return as an error message and request for the user to retry instead of crashing the application?

Answer 1

You never called onProgressUpdate during your doInBackGround(...). Please note that running multiple instances of AsyncTask is a bad idea. Here is what I suggest:

if(isSyncSuccess){
    SetConstant.IMAGE_EXIST=1;
    pDialog=new ProgressDialog(GalleryScreen.this);
    pDialog.setMessage("Downloading file. Please wait...");
    pDialog.setIndeterminate(false);
    pDialog.setProgress(0);
    pDialog.setMax(contentId.length);
    pDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
    pDialog.setCancelable(true);

    new DownloadFile().execute();
}

private class DownloadFiles extends AsyncTask<String, Integer, String> {
    @Override
    protected String doInBackground(String... sUrl) {
        Bitmap bm;
        InputStream in;

        if (contentId.length > 0) {
            for (int i = 0; i < contentId.length; i++) {
                if (helper.databaseChecking(useremail, contentId[i])) {
                    contentdownload = i;
                    SetConstant.CONTENT_ID = contentId[i];

                    String URL = SetConstant.URL_DOWNLOAD_CONTENT + contentId[i];
                    //YOUR INTRESTING LOOP HERE.
                    publishProgress(30);
                    //SOME INTRESTING NUMBER FOR PROGRESS UPDATE
                }
            }

            try {
                in = new java.net.URL(sUrl[0]).openStream();
                bm = BitmapFactory.decodeStream(new PatchInputStream(in));
                File storage = new File(Environment.getExternalStorageDirectory() + File.separator + "/Image/");
                Log.i(TAG, "storage:" + storage);
                Log.i(TAG, "storage:" + storage.getAbsolutePath());
                if (!storage.exists()) {
                    storage.mkdirs();

                }
                String FileName = "/" + SetConstant.CONTENT_ID + ".jpg";
                FileOutputStream fos = new FileOutputStream(storage + FileName);
                bm.compress(Bitmap.CompressFormat.JPEG, 85, fos);

                String filepath = storage + FileName;
                File filecheck = new File(filepath);
                long fileSize = filecheck.length();
                fos.flush();
                fos.close();
            } catch (IOException e1) {
                e1.printStackTrace();
            }

            return null;
        }

        @Override
        protected void onPreExecute () {
            super.onPreExecute();
            pDialog.show();
        }

        @Override
        protected void onProgressUpdate (Integer...progress){
            super.onProgressUpdate(progress);
            pDialog.setProgress(progress[0]);
        }

        protected void onPostExecute (String result){
            super.onPostExecute(result);
            pDialog.dismiss();
        }
    }
}

Of course this code don’t run and you need to fix the scopes. But what I am trying to suggest is that your loop should be in doInBackGround(...), you should only have 1 instance of AsyncTask at given time for this case, and call the onProgressUpdate().