App crashes without catching any exception

Question

So i'm into a tutorial at Udemy "The Complete Android N Developer Course" and trying to make lecture 86 about a weather app.

I use the API from here https://openweathermap.org/current#cityid and use JSON to get the data needed.

The app is working properly when i input a correct city name, but when the input is wrong or empty the app crashes without catching any exceptions.

I don't know why it is crashing and where to look. So i give you all the code i wrote. I tried to implement if statements here and there to try and find it but without any luck.

I would like to know where the problem is and how to fix it so the app doesn't crash anymore.

Thanks in advance.

public class MainActivity extends AppCompatActivity {

    EditText editText;
    String city = "";
    TextView textView;

    public void getWeather (View view)  {
        try {
            city = URLEncoder.encode(editText.getText().toString(), "UTF-8");

            if (editText.getText().toString() == "") {
                Toast.makeText(MainActivity.this, "Could not find weather", Toast.LENGTH_SHORT).show();
                textView.setText("Please enter a city.");
            } else  {
                DownloadTask task = new DownloadTask();
                task.execute("http://api.openweathermap.org/data/2.5/weather?q=" + city + "&appid=c6ef169a79d84674ef7e1414301eb5c4");
            }

            InputMethodManager mgr = (InputMethodManager) getSystemService(Context.INPUT_METHOD_SERVICE);
            mgr.hideSoftInputFromWindow(editText.getWindowToken(), 0);

        } catch (UnsupportedEncodingException e1) {
            Toast.makeText(MainActivity.this, "UnsupportedEncodingException", Toast.LENGTH_SHORT).show();
        }catch (Exception e) {
            Toast.makeText(MainActivity.this, "General exception (getWeather)", Toast.LENGTH_SHORT).show();
        }
    }


    public class DownloadTask extends AsyncTask<String, Void, String> {

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

            String result = "";
            URL url;
            HttpURLConnection urlConnection = null;

            try {
                url = new URL(urls[0]);
                urlConnection = (HttpURLConnection)url.openConnection();
                InputStream in = null;
                in = urlConnection.getInputStream();
                InputStreamReader reader = new InputStreamReader(in);

                int data = reader.read();
                while (data != -1) {
                    char current = (char) data;
                    result += current;
                    data = reader.read();
                }
                return result;
            } catch (MalformedURLException e1) {
                Toast.makeText(MainActivity.this, "MalformedURLException", Toast.LENGTH_SHORT).show();
            } catch (IOException e2) {
            Toast.makeText(MainActivity.this, "IOException", Toast.LENGTH_SHORT).show();
            } catch (Exception e) {
                Toast.makeText(MainActivity.this, "General exception (doInBackground)", Toast.LENGTH_SHORT).show();
            }
            return null;
        }

        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);

            try {
                String message = "";
                JSONObject jsonObject = null;
                jsonObject = new JSONObject(result);
                String weatherInfo = jsonObject.getString("weather");
                JSONArray jsonArray = new JSONArray(weatherInfo);

                for (int i = 0; i < jsonArray.length(); i++)    {

                    JSONObject jsonPart = jsonArray.getJSONObject(i);
                    String main = "";
                    String description = "";

                    main = jsonPart.getString("main");
                    description = jsonPart.getString("description");

                    if (main != "" && description != "")    {
                        message += main + ": " + description + "\r\n";
                    }
                }

                if (message != "") {
                    textView.setText(message);
                } else  {
                    Toast.makeText(MainActivity.this, "Could not find weather", Toast.LENGTH_SHORT).show();
                }
            } catch (JSONException e1) {
                Toast.makeText(MainActivity.this, "JSONException", Toast.LENGTH_SHORT).show();
            } catch (Exception e) {
                Toast.makeText(MainActivity.this, "General exception (onPostExecute)", Toast.LENGTH_SHORT).show();
            }
        }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        editText = (EditText) findViewById(R.id.editText);
        textView = (TextView) findViewById(R.id.textView);

    }
}

Answer 1

It is because you're trying to changes UI with background thread inside the doInBackground(Params...) method of AsyncTask with this line:

try {
     ...
    return result;
} catch (MalformedURLException e1) {
    Toast.makeText(MainActivity.this, "MalformedURLException", Toast.LENGTH_SHORT).show();
} catch (IOException e2) {
Toast.makeText(MainActivity.this, "IOException", Toast.LENGTH_SHORT).show();
} catch (Exception e) {
    Toast.makeText(MainActivity.this, "General exception (doInBackground)", Toast.LENGTH_SHORT).show();
}

You should not call Toast inside the doInBackground(Params...). Do that inside the onPostExecute(Result).

You can avoid that by either ignoring the error or returning specific text in doInBackground. Something like this:

public class DownloadTask extends AsyncTask<String, Void, String> {

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

        String result = "";
        ...

        try {
            ...
            return result;
        } catch (MalformedURLException e1) {
            result= "MalformedURLException";
        } catch (IOException e2) {
            result= "IOException";
        } catch (Exception e) {
            // do nothing and returning empty
            result= "Exception";
        }
        return result;
    }

    @Override
    protected void onPostExecute(String result) {
        // check if there is an error
        String errorMessage = "";
        switch(result) {
          case "MalformedURLException":
            errorMessage = "MalformedURLException";
            break;
          case ""IOException":
            errorMessage = "IOException";
            break;
          case "Exception":
            errorMessage = "Exception";
            break;
        }

         // there is an error, show a message.
        if(!errorMessage.isEmpty()) {
            Toast.makeText(MainActivity.this, "Could not find weather: " + errorMessage, Toast.LENGTH_SHORT).show();
            return; // stop the process.
        }

         // do something when no error found.

    }
}