Android, how to display a dialog from error of a try catch?

Question

In my app I connect to a website to collect some information at start with a AsyncTask, using a try catch, from here I can display in my catlog the error if any at connection, but I have been trying with out luck to show a dialog displaying the connection failure with options to reconnect or quit, please check my code and tell me what I'm doing wrong or an idea of how to accomplish this

 //this is our download file asynctask
class DownloadFileAsync extends AsyncTask<String, String, String> {

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

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

        try {
        String result = "";
                    try {
                        HttpClient httpclient = new DefaultHttpClient();
                        HttpPost httppost = new HttpPost("http://mywebsiteaddress");
                        // httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
                        HttpResponse response = httpclient.execute(httppost);
                        HttpEntity entity = response.getEntity();
                        InputStream webs = entity.getContent();
                        // convert response to string
                        try {
                            BufferedReader reader = new BufferedReader(
                                    new InputStreamReader(webs, "iso-8859-1"), 8);
                            StringBuilder sb = new StringBuilder();
                            String line = null;
                            while ((line = reader.readLine()) != null) {
                                sb.append(line + "\n");
                            }
                            webs.close();

                            result = sb.toString();
                        } catch (Exception e) {
                            Log.e("log_tag", "Error converting result " + e.toString());
                        }
                    } catch (Exception e) {
                        Log.e("log_tag", "Error in http connection " + e.toString());
                    }

                    // parse json data
                    try {
                        JSONArray jArray = new JSONArray(result);
                        for (int i = 0; i < jArray.length(); i++) {
                            JSONObject json_data = jArray.getJSONObject(i);
                            webResult resultRow = new webResult();
                            //infotodownload
                            arrayOfWebData.add(resultRow);

                        }
                    } catch (JSONException e) {
                        Log.e("log_tag", "Error parsing data " + e.toString());
                    }
    } catch (Exception e) {
        // this is the line of code that sends a real error message to the
        // log
        Log.e("ERROR", "ERROR IN CODE: " + e.toString());
        // this is the line that prints out the location in
        // the code where the error occurred.
        e.printStackTrace();
    }
        return null;
    }

    protected void onProgressUpdate(String... progress) {
         Log.d(LOG_TAG,progress[0]);
         mProgressDialog.setProgress(Integer.parseInt(progress[0]));
    }

    @Override
    protected void onPostExecute(String unused) {
        //dismiss the dialog after the file was downloaded
        dismissDialog(DIALOG_DOWNLOAD_PROGRESS);
    }

}

//our progress bar settings
@Override
protected Dialog onCreateDialog(int id) {
    switch (id) {
        case DIALOG_DOWNLOAD_PROGRESS: //we set this to 0
            mProgressDialog = new ProgressDialog(this);
            mProgressDialog.setTitle("Conectando al Servidor");
            mProgressDialog.setMessage("Cargando informacion...");
            mProgressDialog.setIndeterminate(false);
            mProgressDialog.setMax(100);
            mProgressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
            mProgressDialog.setCancelable(true);
            mProgressDialog.show();
            return mProgressDialog;
        default:
            return null;
    }
}

EDIT: then I have try adding the next code as of suggested by Arun

 catch (Exception e) {
        // this is the line of code that sends a real error message to the
        // log
        Log.e("ERROR", "ERROR IN CODE: " + e.toString());
        // this is the line that prints out the location in
        // the code where the error occurred.
        e.printStackTrace();
        return "ERROR_IN_CODE";
    }
       return null;       // if I place here return "ERROR_IN_CODE" it calls the dialog but it gets always called so I don't need it here
    }

    @Override
    protected void onPostExecute(String unused) {
        //dismiss the dialog after the file was downloaded
        dismissDialog(DIALOG_DOWNLOAD_PROGRESS);
        if(unused.equals("ERROR_IN_CODE")){                 //I get a system crash here!
            errornote();
        }
    }

}

public void errornote() {
    AlertDialog.Builder alt_bld = new AlertDialog.Builder(this);
    alt_bld.setMessage("No se a podido descargar la informacion de los medios, deseas reintentarlo, o salir?").setCancelable(false)
            .setPositiveButton("Conectar de Nuevo", new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int id) {
                    new DownloadFileAsync().execute();
                }
            })
            .setNegativeButton("Salir", new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int id) {
                    // Action for 'NO' Button
                    finish();
                }
            });
    AlertDialog alert = alt_bld.create();
    // Title for AlertDialog
    alert.setTitle("Error en la Conexion!");
    // Icon for AlertDialog
    alert.setIcon(android.R.drawable.ic_dialog_alert);
    alert.show();
}

but not working either, my app crashes in the if statement line in onPostExecute. I still need help.

Answer 1

you are not using the builder to create AlertDialog remove the line builder.show() and add

AlertDialog alert = builder.create();
alert.show();

I will also recommend that do the UI updates through progressUpdate() or preExecute() and 'postExecute()' of the asyc task.

Implementation

@ReactMethod
    public void showCustomAlert(String msg){

        final String message = msg;

        this.reactContext.runOnUiQueueThread(new Runnable() {
            @Override
            public void run() {
                AlertDialog.Builder myDialogBox = new AlertDialog.Builder(reactContext.getCurrentActivity());
                myDialogBox.setTitle(Html.fromHtml("<font color='#0037FF'>Konnect</font>"));
                myDialogBox.setMessage(message);
                myDialogBox.setCancelable(true);
                myDialogBox.setPositiveButton("Ok", new DialogInterface.OnClickListener(){

                    public void onClick(DialogInterface dialog, int whichButton) {
                            dialog.dismiss();
                    }

                });
                AlertDialog alertDialog = myDialogBox.create();
                if (Build.VERSION.SDK_INT <= 23) {
                    alertDialog.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);
                }else if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                    alertDialog.getWindow().setType(WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY);
                }else {
                    alertDialog.getWindow().setType(WindowManager.LayoutParams.TYPE_PHONE);
                }

                alertDialog.show();

                WindowManager.LayoutParams wmlp = alertDialog.getWindow().getAttributes();
                wmlp.gravity = Gravity.TOP | Gravity.LEFT;
                wmlp.x = 25;   //x position
                wmlp.y = 450;   //y position
                wmlp.height = 380;
                alertDialog.show();
                alertDialog.getWindow().setBackgroundDrawable(new ColorDrawable(Color.WHITE));
            }
        });
    }

Answer 2

Since you are returning a String object from the protected String doInBackground(String... aurl) return some custom Error String from the catch block and access it in the protected void onPostExecute(String unused). Check if the returned String object is the Custom Error String and show the dialog in protected void onPostExecute(String unused) but only after dismissing the progressDialog i.e. after this line dismissDialog(DIALOG_DOWNLOAD_PROGRESS); show the error dialog.

EDIT

When the control enters the Catch block return some simple String like the one you used "ERROR_IN_CODE".

catch (Exception e) {
    // this is the line of code that sends a real error message to the
    // log
    Log.e("ERROR", "ERROR IN CODE: " + e.toString());
    // this is the line that prints out the location in
    // the code where the error occurred.
    e.printStackTrace();

    return "ERROR_IN_CODE";
}

And in the onPostExecute(String unused) check for the following

protected void onPostExecute(String unused) {
    //dismiss the dialog after the file was downloaded
    dismissDialog(DIALOG_DOWNLOAD_PROGRESS);
    if(unused != null && unused.equals("ERROR_IN_CODE")){
        showDialog(SOME_DIALOG_TO_SHOW_ERROR);
    }
}

Answer 3

Try calling your activities runOnUiThread() method

activity.runOnUiThread(new Runnable() {
        public void run() {
            //your alert dialog builder here
    });