Download images with AsyncTask

Issue

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?

Solution

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().

Answered By - wtsang02