Question

I am developing an android app in which i need to display images after downloading them from server and when the downloading is proceeding a progress dialog is being show. For that i an using an asynctask class.
I am using t he following source code for it.

           private void startDownload() {

    new DownloadFileAsync().execute(imageUrl);
    image.setImageBitmap(bitmap);
}
 @Override
    protected Dialog onCreateDialog(int id) {
        switch (id) {
            case DIALOG_DOWNLOAD_PROGRESS:
                dialog = new ProgressDialog(this);
                dialog.setTitle("Loading");
                dialog.setMessage("Please wait...");
                dialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
                dialog.setCancelable(false);
                dialog.show();
                return dialog;
            default:
                return null;
        }
    }


 class DownloadFileAsync extends AsyncTask<String, String, String> {
     int count;
     URL myFileUrl;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            showDialog(DIALOG_DOWNLOAD_PROGRESS);
        }

        @Override
        protected String doInBackground(String... aurl) {


            try {
                myFileUrl = new URL(imageUrl);
                HttpURLConnection conn = (HttpURLConnection) myFileUrl
                        .openConnection();
                int lenghtOfFile = conn.getContentLength();
                //conn.setDoInput(true);
                conn.setConnectTimeout(10000);
                conn.setReadTimeout(10000);
                conn.connect();
                InputStream is = conn.getInputStream();
                bmImg = BitmapFactory.decodeStream(is);
                bitmap = BitmapFactory.decodeStream((InputStream) new URL(imageUrl)
                        .getContent());
                bitmap = Bitmap.createScaledBitmap(bitmap, 70, 70, true);

                  byte data[] = new byte[1024];
                  System.out.println("mmmmmmmmmmmm");

                    long total = 0;
                    System.out.println("nnnnnnnnnn");
                    while ((count = ((InputStream) new URL(imageUrl)
                    .getContent()).read(data)) != -1) {
                        total += count;
                        publishProgress(""+(int)((total*100)/lenghtOfFile));
                        for(int l=0;l<4;l++){
                        if(listObject.get(l).getImage()!="")
                       image.setImageBitmap(bitmap);
                    }}

            }
            catch(Exception e){
                System.out.println(e);}

        return null;
        }

        protected void onProgressUpdate(String... progress) {
            dialog.setProgress(Integer.parseInt(progress[0]));
        }

        @Override
        protected void onPostExecute(String unused) {
            image.setImageBitmap(bitmap);
            dismissDialog(DIALOG_DOWNLOAD_PROGRESS);

        }
        }

But it giving the following exception.:

android.view.ViewRoot$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views. 

i am unable to figure out the problem. Can anyone help me over this.
Thanks

Answer 1

This is your problem:

for(int l=0;l<4;l++){
    if(listObject.get(l).getImage()!="")
        image.setImageBitmap(bitmap);
}

Short answer: just like the exception says, you’re trying to manipulate a view in the wrong thread. Do it in the right thread (UI thread).

Long answer: In an AsyncTask the right places to do view manipulation are generally onPreExecute, onProgressUpdate and onPostExecute. doInBackground is not usually a good place to modify views. You could call back to the UI thread in one of many ways (for example you could use post). However, that block of code that you posted doesn’t make a whole lot of sense to me in general, and you haven’t shown enough context to explain what it is, what listObject is, etc.

You have some other problems too. You seem to be trying to read the data in twice in a row in two different ways… Also, I imagine your while condition is going to give you problems as you’re recreating the URL object and as long as you get content back you’re going to keep doing it. Assuming that URL doesn’t have dynamic content, you’ll have an infinite loop.