How to start an activity only if a condition is met

Question

I am a beginner in Android development, My app requires users to enter their email and password in the LoginActivity in order to login. If the credentials are okay, then the app should start the WorkActivity.

Here is the PHP script. For testing, I have just set $email and $password as static values rather than grabbing them from a database.

<?php 
$response = array ("success"=> 0, "responseMessage"=> "Incorrect email/password combination");

$email = "mwangicj";
$password = "asd";
if($_SERVER['REQUEST_METHOD']=='POST'){
 $request = json_decode(file_get_contents('php://input'));
 if(!strcmp($email,$request->email)&& !strcmp($password,$request->password)){
  $response['success'] = 1;
  $response['responseMessage'] = "Login successful ".$request->email;
 }
}
echo json_encode($response);
?>

I am using Volley library to send and receive data to and from the PHP. Here is the LoginActivity

package com.mwangicj.Lugayocontributor;

import android.content.Intent;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

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.JsonObjectRequest;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;

import org.json.JSONException;
import org.json.JSONObject;

import java.util.HashMap;
import java.util.Map;

public class LoginActivity extends AppCompatActivity {
    EditText loginEmail, loginPassword;
    TextView message;
    Button loginButton;

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

        loginEmail = (EditText) findViewById(R.id.loginEmail);
        loginPassword = (EditText) findViewById(R.id.loginPassword);
        loginButton = (Button) findViewById(R.id.loginButton);
        message = (TextView) findViewById(R.id.message);

        loginButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (connected()){
                    message.setText("");
                    String email = loginEmail.getText().toString();
                    String password = loginPassword.getText().toString();

                    if  (!email.isEmpty() && !password.isEmpty()){ //Check if fields are filled in
                        logInUser();
                    }else{
                        Toast.makeText(getApplicationContext(), "Supply both email and password!",Toast.LENGTH_LONG).show();
                    }
                }else{
                    Toast.makeText(getApplicationContext(), "No internet", Toast.LENGTH_SHORT).show();
                }

            }
        });
    }
    //executing user's login request
    private void logInUser() {
        
        postJsonRequest("http://10.0.2.2:1234/app/json.php");
    }
    //Starting work activity
    void goToWork(){
         Intent i = new Intent(getApplicationContext(), WorkActivity.class);
        startActivity(i);
        finish();
    }

    //preparing user's login details
    private void postJsonRequest(String url) {
        RequestQueue queue = Volley.newRequestQueue(getApplicationContext());
        JSONObject params = new JSONObject();
        try {
            params.put("email", loginEmail.getText().toString());
            params.put("password", loginPassword.getText().toString());
        } catch (JSONException e) {
            e.printStackTrace();
        }

        JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(
                Request.Method.POST, url, params, new Response.Listener<JSONObject>(){

            @Override
            public void onResponse(JSONObject response) {
                try {
                    String success = response.getString("success");
                    String responseMessage = response.getString("responseMessage");
                    if (success == "0"){
                        message.setText(responseMessage);
                    }else{
                        Toast.makeText(getApplicationContext(), responseMessage, Toast.LENGTH_LONG).show();
                        goToWork();

                    }
                } catch (JSONException e) {
                    e.printStackTrace();
                }
            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                message.setText("Error: " + error.toString());

            }
        });
        queue.add(jsonObjectRequest);
    }

    //Checking internet connection
    boolean connected (){
        ConnectivityManager cManager = (ConnectivityManager) getSystemService(this.CONNECTIVITY_SERVICE);
        NetworkInfo nInfo = cManager.getActiveNetworkInfo();

        if(nInfo!=null && nInfo.isConnected()){
            return true;
        }else{
            return false;
        }
    }
}

The problem is the WorkActivity is starting regardless of correct or incorrect email and password combination.

How do I fix this?

Have you tried stepping through the code in a debugger? – rrirower Jun 21 '16 at 12:22 — rrirower, Jun 21 '16 at 12:22

score 2 · Accepted Answer · edited May 23 '17 at 12:16

The problem is the == operator checks for reference equality when comparing objects. To test two strings for value equality, you should use the equals() method instead.

From the documentation of String.equals():

public boolean equals(Object anObject)

Compares this string to the specified object. The result is true if and only if the argument is not null and is a String object that represents the same sequence of characters as this object.

Change the following:

if (success == "0"){
    message.setText(responseMessage);
}

To this:

if ("0".equals(success)){
    message.setText(responseMessage);
}

OR

Declare success as a primitive int, rather than a String:

int success = response.getInt("success");
String responseMessage = response.getString("responseMessage");
if (success == 0){
    message.setText(responseMessage);
}

Check out this answer on String equality.

How to start an activity only if a condition is met

1 Answers1