Back Button im my App crashes (Unfortunately, Frienday's has stopped.)

Question

I am trying to create an app where a user can login and logout.
When they login, they are presented with an activity that displays their email and name (from a database).

I recently added a navbar back option. When the user goes to the navbar and selects a page (about, settings, etc.), they will go to that Activity. If the back Button is pressed to go to the logged in the Activity (LoginSuccess.java), the app crashes displaying "Unfortunately Frienday's has stopped running."

I have tried to debug this, and it's leading me to a NullPointerException in LoginSuccess.java. I tried removing the items in the LoginSuccess.java file that make the name and email of the user appear. If these are removed, the back button will work fine.

LoginSuccess.java file

TextView name, email;

protected void onCreate(Bundle savedInstanceState) {
    ...
    name = (TextView) findViewById(R.id.name);
    email = (TextView) findViewById(R.id.name);
    Bundle bundle = getIntent().getExtras();
    name.setText(bundle.getString("name"));
    email.setText("Email: " + bundle.getString("email"));
}

login.php file (for database)

<?php
    require "init.php";

    $user_name = $_POST["user_name"];
    $password = $_POST["password"];

    $sql = "SELECT name,email FROM user_info WHERE user_name LIKE   '".$user_name."' AND password LIKE '".$password."';";

    $result = mysqli_query($con, $sql);
    $response = array();

    # Check if user already exists.
    if (mysqli_num_rows($result) > 0)
    {
        $row = mysqli_fetch_row($result);
        $name = $row[0];
        $email = $row[1];
        $code = "login_success";
        array_push($response, array ("code" => $code, "name" => $name, "email" => $email));
        echo json_encode($response);
    }
    else
    {
        $code = "login_failed";
        $message = "User not found... Please try again!";
        array_push($response, array("code" => $code, "message" => $message));
        echo json_encode($response);
    }

    mysqli_close($con);

?>

Logcat

E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.goril.friendays, PID: 32166
              java.lang.RuntimeException: Unable to start activity ComponentInfo{com.goril.friendays/com.goril.friendays.LoginSuccess}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.os.Bundle.getString(java.lang.String)' on a null object reference
                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3254)
                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3350)
                  at android.app.ActivityThread.access$1100(ActivityThread.java:222)
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1795)
                  at android.os.Handler.dispatchMessage(Handler.java:102)
                  at android.os.Looper.loop(Looper.java:158)
                  at android.app.ActivityThread.main(ActivityThread.java:7237)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
               Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.os.Bundle.getString(java.lang.String)' on a null object reference
                  at com.goril.friendays.LoginSuccess.onCreate(LoginSuccess.java:25)
                  at android.app.Activity.performCreate(Activity.java:6876)
                  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1135)
                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3207)
                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3350) 
                  at android.app.ActivityThread.access$1100(ActivityThread.java:222) 
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1795) 
                  at android.os.Handler.dispatchMessage(Handler.java:102) 
                  at android.os.Looper.loop(Looper.java:158) 
                  at android.app.ActivityThread.main(ActivityThread.java:7237) 
                  at java.lang.reflect.Method.invoke(Native Method) 
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

I have been struggling with this for a few days. If anyone could help me I would gladly appreciate it :). I implemented the back option from the Android website tutorial.

Tutorial: https://developer.android.com/training/implementing-navigation/ancestral.html

OneCricketeer · Answer 1 · 2017-02-17T00:11:39.920

1

When you press back, getIntent() doesn't exist from the previous Activity that started that activity, therefore it'll be null.

You can catch that like so

Bundle extras = getIntent().getExtras();
if (extras != null) {
    name.setText(bundle.getString("name"));
    email.setText("Email: " + bundle.getString("email"));
}

edited Feb 17 '17 at 00:11

answered Feb 17 '17 at 00:06

OneCricketeer

126,858
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So how would I change this? I'm new to Android Dev.. – D. Ross Feb 17 '17 at 00:08
You should probably store login data within SharedPreferences. For example. http://www.androidhive.info/2012/08/android-session-management-using-shared-preferences/ – OneCricketeer Feb 17 '17 at 00:10
So temporarily, I can catch this error with the if statement, but I should be using SharedPreferences in the long run correct? – D. Ross Feb 17 '17 at 00:13
You can. Doesn't mean that you necessarily should. – OneCricketeer Feb 17 '17 at 00:15
Okay, Thanks for the help! – D. Ross Feb 17 '17 at 00:17
The SharedPreferences wasn't working for me, is there another way to get the intent in LoginSuccess.java every time I go into that activity? – D. Ross Feb 17 '17 at 01:05
Try that link again. SharedPrefences definitely work. They won't just fix your nullpointerexception, you need to save and get data from it correctly (separately from using an Intent) – OneCricketeer Feb 17 '17 at 02:12

score 0 · Answer 2 · edited Feb 17 '17 at 00:05

0

I think you have already the explanation there, try to read it :

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.os.Bundle.getString(java.lang.String)' on a null object reference

The bundle is null and you are trying to get a string on a null object. You need to check for null.

edited Feb 17 '17 at 00:05

OneCricketeer

126,858
14
92
185

answered Feb 17 '17 at 00:04

Romulano

236
2
7

But when I remove the stuff shown in LoginSuccess.java, it works fine :o – D. Ross Feb 17 '17 at 00:07
What would I do if it returns null? How would I present the user with their email / name? – D. Ross Feb 17 '17 at 00:09

Back Button im my App crashes (Unfortunately, Frienday's has stopped.)

2 Answers2