Users.java

import android.app.ProgressDialog;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;
 
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;
 
import org.json.JSONException;
import org.json.JSONObject;
 
import java.util.ArrayList;
import java.util.Iterator;
 
public class Users extends AppCompatActivity {
    ListView usersList;
    TextView noUsersText;
    ArrayList<String> al = new ArrayList<>();
    int totalUsers = 0;
    ProgressDialog pd;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_users);
 
        usersList = (ListView)findViewById(R.id.usersList);
        noUsersText = (TextView)findViewById(R.id.noUsersText);
 
        pd = new ProgressDialog(Users.this);
        pd.setMessage("Loading...");
        pd.show();
 
        String url = "https://androidchatapp-76776.firebaseio.com/users.json";
 
        StringRequest request = new StringRequest(Request.Method.GET, url, new Response.Listener<String>(){
            @Override
            public void onResponse(String s) {
                doOnSuccess(s);
            }
        },new Response.ErrorListener(){
            @Override
            public void onErrorResponse(VolleyError volleyError) {
                System.out.println("" + volleyError);
            }
        });
 
        RequestQueue rQueue = Volley.newRequestQueue(Users.this);
        rQueue.add(request);
 
        usersList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                UserDetails.chatWith = al.get(position);
                startActivity(new Intent(Users.this, Chat.class));
            }
        });
    }
 
    public void doOnSuccess(String s){
        try {
            JSONObject obj = new JSONObject(s);
 
            Iterator i = obj.keys();
            String key = "";
 
            while(i.hasNext()){
                key = i.next().toString();
 
                if(!key.equals(UserDetails.username)) {
                    al.add(key);
                }
 
                totalUsers++;
            }
 
        } catch (JSONException e) {
            e.printStackTrace();
        }
 
        if(totalUsers <=1){
            noUsersText.setVisibility(View.VISIBLE);
            usersList.setVisibility(View.GONE);
        }
        else{
            noUsersText.setVisibility(View.GONE);
            usersList.setVisibility(View.VISIBLE);
            usersList.setAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, al));
        }
 
        pd.dismiss();
    }
}