android - Arraylist of strings into one comma separated string

Trying to convert a Arraylist of strings into one big comma separated string.

However when I use the

String joined = TextUtils.join(", ", participants);

Debugger shows me size of 4 for participants however the joined value as "" therefore empty

private ArrayList participants;

Not sure what is going wrong?

UPDATE:

List list = new ArrayList<>();
list.add("Philip");
list.add("Paul Smith");
list.add("Raja");
list.add("Ez");

String s = TextUtils.join(", ", list);

This works when I have a list that I manually populate however below is how the code is working right now.

In the onCreate()

callApi(type);
String s = TextUtils.join(", ", participants);
getSupportActionBar().setTitle(s);

In callAPI():

JSONArray participantsR = sub.getJSONArray("referralParticipants");

Log.e("Participants length ", String.valueOf(participantsR.length()));

for (int i = 0; i < participantsR.length(); i++)
{
    JSONObject object = participantsR.getJSONObject(i);
    String firstname = (String) object.get("fullName");
    participants.add(firstname);
    Log.e("Times", String.valueOf(i));

}

Answer

I'm trying to reproduce your error and am unable to. Here is my code:

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


    List list = new ArrayList<>();
    list.add("Philip Johnson");
    list.add("Paul Smith");
    list.add("Raja P");
    list.add("Ezhu Malai");

    String s = TextUtils.join(", ", list);

    Log.d(LOGTAG, s);
}

My output is Philip Johnson, Paul Smith, Raja P, Ezhu Malai as expected.

Are you importing the correct TextUtils class?

android.text.TextUtils;

Given the new information, here is my approach:

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

    callApi(type, new OnResponseListener>() {
        @Override public void onResponse(List list) {
            getSupportActionBar().setTitle(TextUtils.join(", ", list));
        }
    });

}

I don't know what networking library you're using, but you may have to define OnResponseListener as an interface. It's very easy:

public interface OnResponseListener {
    public void onResponse(T response);
}

You will then need to modify your callApi function to take an instance of OnResponseListener> and call it's onResponse method after completing the call.

I would recommend looking into the Volley library, and reading the Android documentation about simple network calls.