Android AsyncTask [Can't create handler inside thread that has not called Looper.prepare()]

I've created an image upload `AsyncTask` based on a function. And after uploading, I get this error on `onPostExecute()`. I read up some StackOverflow answers on `Runnable` yet I kept getting the error over and over again despite implementing a different solution. My code : ``` class uploadFile extends AsyncTask<String, String, String> { private ProgressDialog pDialog; /** * -------------------------------------------------------------------- * --------------------------------- Before starting background thread * Show Progress Dialog */ @Override protected void onPreExecute() { super.onPreExecute(); pDialog = new ProgressDialog(MainActivity.this); pDialog.setMessage("Uploading file"); pDialog.setIndeterminate(false); pDialog.setCancelable(false); pDialog.show(); } /** * -------------------------------------------------------------------- * --------------------------------- getting all recent articles and * showing them in listview */ @Override protected String doInBackground(String... args) { HttpURLConnection conn = null; DataOutputStream dos = null; DataInputStream inStream = null; String existingFileName = Environment.getExternalStorageDirectory() .getAbsolutePath() + "/mypic.png"; String lineEnd = "\r\n"; String twoHyphens = "--"; String boundary = "*****"; int bytesRead, bytesAvailable, bufferSize; byte[] buffer; int maxBufferSize = 1 * 1024 * 1024; String serverResponseMessage = ""; String urlString = "http://google.info/imgupl/index.php"; try { // ------------------ CLIENT REQUEST FileInputStream fileInputStream = new FileInputStream(new File( existingFileName)); // open a URL connection to the Servlet URL url = new URL(urlString); // Open a HTTP connection to the URL conn = (HttpURLConnection) url.openConnection(); // Allow Inputs conn.setDoInput(true); // Allow Outputs conn.setDoOutput(true); // Don't use a cached copy. conn.setUseCaches(false); // Use a post method. conn.setRequestMethod("POST"); conn.setRequestProperty("Connection", "Keep-Alive"); conn.setRequestProperty("Content-Type", "multipart/form-data;boundary=" + boundary); dos = new DataOutputStream(conn.getOutputStream()); dos.writeBytes(twoHyphens + boundary + lineEnd); dos.writeBytes("Content-Disposition: form-data; name=\"uploadedfile\";filename=\"" + existingFileName + "\"" + lineEnd); dos.writeBytes(lineEnd); // create a buffer of maximum size bytesAvailable = fileInputStream.available(); bufferSize = Math.min(bytesAvailable, maxBufferSize); buffer = new byte[bufferSize]; // read file and write it into form... bytesRead = fileInputStream.read(buffer, 0, bufferSize); while (bytesRead > 0) { dos.write(buffer, 0, bufferSize); bytesAvailable = fileInputStream.available(); bufferSize = Math.min(bytesAvailable, maxBufferSize); bytesRead = fileInputStream.read(buffer, 0, bufferSize); } // send multipart form data necesssary after file data... dos.writeBytes(lineEnd); dos.writeBytes(twoHyphens + boundary + twoHyphens + lineEnd); // close streams Integer serverResponseCode = conn.getResponseCode(); serverResponseMessage = conn.getResponseMessage(); Toast.makeText(getApplicationContext(), serverResponseMessage, Toast.LENGTH_SHORT).show(); Toast.makeText(getApplicationContext(), serverResponseCode.toString(), Toast.LENGTH_SHORT) .show(); Log.e("Debug", "File is written"); fileInputStream.close(); dos.flush(); dos.close(); } catch (MalformedURLException ex) { Log.e("Debug", "error: " + ex.getMessage(), ex); } catch (IOException ioe) { Log.e("Debug", "error: " + ioe.getMessage(), ioe); } // ------------------ read the SERVER RESPONSE try { inStream = new DataInputStream(conn.getInputStream()); while ((str = inStream.readLine()) != null) { Log.e("Debug", "Server Response " + str); } inStream.close(); } catch (IOException ioex) { Log.e("Debug", "error: " + ioex.getMessage(), ioex); } return null; } /** * -------------------------------------------------------------------- * --------------------------------- After completing background task * Dismiss the progress dialog **/ protected void onPostExecute(String args) { // dismiss the dialog after getting all products pDialog.dismiss(); MainActivity.this.runOnUiThread(new Runnable() { public void run() { Toast.makeText(MainActivity.this, "Hello", Toast.LENGTH_SHORT).show(); } }); } } ``` My logcat : ``` 08-13 22:13:32.627: E/AndroidRuntime(9554): FATAL EXCEPTION: AsyncTask #1 08-13 22:13:32.627: E/AndroidRuntime(9554): java.lang.RuntimeException: An error occured while executing doInBackground() 08-13 22:13:32.627: E/AndroidRuntime(9554): at android.os.AsyncTask$3.done(AsyncTask.java:200) 08-13 22:13:32.627: E/AndroidRuntime(9554): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274) 08-13 22:13:32.627: E/AndroidRuntime(9554): at java.util.concurrent.FutureTask.setException(FutureTask.java:125) 08-13 22:13:32.627: E/AndroidRuntime(9554): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308) 08-13 22:13:32.627: E/AndroidRuntime(9554): at java.util.concurrent.FutureTask.run(FutureTask.java:138) 08-13 22:13:32.627: E/AndroidRuntime(9554): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088) 08-13 22:13:32.627: E/AndroidRuntime(9554): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581) 08-13 22:13:32.627: E/AndroidRuntime(9554): at java.lang.Thread.run(Thread.java:1019) 08-13 22:13:32.627: E/AndroidRuntime(9554): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare() 08-13 22:13:32.627: E/AndroidRuntime(9554): at android.os.Handler.<init>(Handler.java:121) 08-13 22:13:32.627: E/AndroidRuntime(9554): at android.widget.Toast.<init>(Toast.java:68) 08-13 22:13:32.627: E/AndroidRuntime(9554): at android.widget.Toast.makeText(Toast.java:231) 08-13 22:13:32.627: E/AndroidRuntime(9554): at dev.google.imageupload.MainActivity$uploadFile.doInBackground(MainActivity.java:128) 08-13 22:13:32.627: E/AndroidRuntime(9554): at dev.google.imageupload.MainActivity$uploadFile.doInBackground(MainActivity.java:1) 08-13 22:13:32.627: E/AndroidRuntime(9554): at android.os.AsyncTask$2.call(AsyncTask.java:185) 08-13 22:13:32.627: E/AndroidRuntime(9554): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306) 08-13 22:13:32.627: E/AndroidRuntime(9554): ... 4 more ``` EDITED after zapl's suggestion : ``` 08-13 22:38:06.297: E/AndroidRuntime(11511): FATAL EXCEPTION: AsyncTask #1 08-13 22:38:06.297: E/AndroidRuntime(11511): java.lang.RuntimeException: An error occured while executing doInBackground() 08-13 22:38:06.297: E/AndroidRuntime(11511): at android.os.AsyncTask$3.done(AsyncTask.java:200) 08-13 22:38:06.297: E/AndroidRuntime(11511): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274) 08-13 22:38:06.297: E/AndroidRuntime(11511): at java.util.concurrent.FutureTask.setException(FutureTask.java:125) 08-13 22:38:06.297: E/AndroidRuntime(11511): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308) 08-13 22:38:06.297: E/AndroidRuntime(11511): at java.util.concurrent.FutureTask.run(FutureTask.java:138) 08-13 22:38:06.297: E/AndroidRuntime(11511): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088) 08-13 22:38:06.297: E/AndroidRuntime(11511): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581) 08-13 22:38:06.297: E/AndroidRuntime(11511): at java.lang.Thread.run(Thread.java:1019) 08-13 22:38:06.297: E/AndroidRuntime(11511): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare() 08-13 22:38:06.297: E/AndroidRuntime(11511): at android.os.Handler.<init>(Handler.java:121) 08-13 22:38:06.297: E/AndroidRuntime(11511): at android.widget.Toast.<init>(Toast.java:68) 08-13 22:38:06.297: E/AndroidRuntime(11511): at android.widget.Toast.makeText(Toast.java:231) 08-13 22:38:06.297: E/AndroidRuntime(11511): at dev.google.imageupload.MainActivity$uploadFile.doInBackground(MainActivity.java:128) 08-13 22:38:06.297: E/AndroidRuntime(11511): at dev.google.imageupload.MainActivity$uploadFile.doInBackground(MainActivity.java:1) 08-13 22:38:06.297: E/AndroidRuntime(11511): at android.os.AsyncTask$2.call(AsyncTask.java:185) 08-13 22:38:06.297: E/AndroidRuntime(11511): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306) 08-13 22:38:06.297: E/AndroidRuntime(11511): ... 4 more ```