startActivity not working after class switch

Question

I want to start an activity and give out a Toast message after I parsed a JSON response.

public class Sign_Up extends AppCompatActivity {

  ....

  register();


  public void register()
  {
  final String url = "someURL";

        new Json().checkJsonFile(url,getApplicationContext());
  }

  //Now in an non-activity

  public class Json {

    public void checkJsonFile(final String url, final Context context) {

        new Thread(new Runnable() {
            public void run() {
                String result;
                String line;

                try {

                    URL obj = new URL(url);
                    HttpURLConnection conn = (HttpURLConnection) obj.openConnection();
                    conn.setReadTimeout(5000);
                    conn.addRequestProperty("Accept-Language", "en-US,en;q=0.8");
                    conn.addRequestProperty("User-Agent", "Mozilla");
                    conn.addRequestProperty("Referer", "google.com");


                    boolean redirect = false;

                    // normally, 3xx is redirect
                    int status = conn.getResponseCode();
                    if (status != HttpURLConnection.HTTP_OK) {
                        if (status == HttpURLConnection.HTTP_MOVED_TEMP
                                || status == HttpURLConnection.HTTP_MOVED_PERM
                                || status == HttpURLConnection.HTTP_SEE_OTHER)
                            redirect = true;
                    }

                    if (redirect) {

                        // get redirect url from "location" header field
                        String newUrl = conn.getHeaderField("Location");

                        // get the cookie if need, for login
                        String cookies = conn.getHeaderField("Set-Cookie");

                        // open the new connnection again
                        conn = (HttpURLConnection) new URL(newUrl).openConnection();
                        conn.setRequestProperty("Cookie", cookies);
                        conn.addRequestProperty("Accept-Language", "en-US,en;q=0.8");
                        conn.addRequestProperty("User-Agent", "Mozilla");
                        conn.addRequestProperty("Referer", "google.com");


                    }

                    BufferedReader in = new BufferedReader(
                            new InputStreamReader(conn.getInputStream()));

                    StringBuilder sb = new StringBuilder();

                    while ((line = in.readLine()) != null) {
                        sb.append(line);

                    }
                    in.close();

                    result = sb.toString();

                    new Sign_Up().parseJSON(result);

                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }
}


        //Back in Sign_Up class

        public void parseJSON(String JSON){
        int error = -1;
        try {
                JSONObject jsonObject = new JSONObject(JSON);

                error = Integer.parseInt(jsonObject.getString("error_code"));

        } catch (JSONException e) {
            //Retry
            register();

            e.printStackTrace();
        }

        progressDialog.dismiss();

        switch (error) {
            case 0: //Successful
                finish();
                startActivity(new Intent(Sign_Up.this, Loading.class));
                break;
            case 1:
                Toast.makeText(getApplicationContext(), "blabla", Toast.LENGTH_SHORT).show();
                break;
            case 2:
                Toast.makeText(getApplicationContext(), "other blabla", Toast.LENGTH_SHORT).show();
                break;
            default:
                register();
                break;
        }
    }

However, when I put the Json stuff inside the Sign_Up class at least the startActivity works, but the Toast doesn't. As well, I would like to have the Json stuff in an seperate class.

Thank you very much in advance!

Tyler V · Accepted Answer · 2018-07-29T15:25:43.353

You cannot create an Activity by calling

new MyActivity()

and expect anything to work. The line

new Sign_Up().parseJSON(result);

is creating a new instance of the Sign_Up activity improperly, so it is not bound to a context and none of its lifecycle calls will be executed. You can't show a Toast in that state.

A better solution would be to pass an interface from Sign_Up into the Json class to let it call back to the original Sign_Up instance rather than trying to make a new instance. For example:

class Json {
    public interface Callback {
        public void run(String result);    
    }

    private Callback callback

    Json(Callback c) {
        callback = c;
    }

    // later, replace new Sign_Up().parseJSON(result) with callback.run(result)
}

and to create it replace

new Json().checkJsonFile(url,getApplicationContext());

with

new Json(new Json.Callback() {
    @Override
    public void run(String result) {
        parseJSON(result);
    }
}).checkJsonFile(url,getApplicationContext());

You'll also want to make sure that all UI operations (toast generation) are being run on the UI thread.

Very awesome! I've thought about that stuff, but wanted to be sure and asked here before. Thank you very much :) — Tester2, Jul 30 '18 at 00:37
Hi Tyler, could you maybe have a look on this as well, would really appreciate it :) https://stackoverflow.com/questions/51662401/getstring-and-dialoglistener-doesnt-work-after-class-switch — Tester2, Aug 02 '18 at 21:31

startActivity not working after class switch

1 Answers1