code

   private void empiezaDescarga(String url) {


    	descarga=new DownloadFileAsync().execute(url);
    }

class DownloadFileAsync extends AsyncTask<String, String, String> {
    	String sTexto;

        @Override
        protected void onCancelled() {
        	super.onCancelled();
        	File file=new File(sRutaFichero);
        	if (file.exists())
        		file.delete();


        }

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            mProgressDialog = new ProgressDialog(contexto);
            mProgressDialog.setMessage(contexto.getString(R.string.DescargaFichero));
            mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
            mProgressDialog.setCancelable(true);  //establecemos que es cancelable.
            mProgressDialog.setOnCancelListener(new OnCancelListener(){

            	@Override
            	public void onCancel(DialogInterface dialog)
            	{
            		descarga.cancel(true);

            	}
            });
            mProgressDialog.show();
        }

 @Override
        protected String doInBackground(String... aurl) {
            int count;

            try {

	            	if(this.isCancelled()){ return null; }

	                URL url = new URL(aurl[0]);
	                URLConnection conexion = url.openConnection();
	                conexion.setConnectTimeout(TIME_OUT);
	                conexion.connect();


	                if(this.isCancelled()){ return null; }

	               ///// some code
            return null;

        }

        protected void onProgressUpdate(String... progress) {

             mProgressDialog.setProgress(Integer.parseInt(progress[0]));
        }

 @Override
        protected void onPostExecute(String unused) {
        mProgressDialog.dismiss();

// Some code
}