Android - Null Array. Runs in Android Studio emulator but not on real device when unplugged

Question

I've been testing my app in Android Studio emulator through my Samsung S7 phone (API 23 and 6.0.1) and it works fine. When I unplug it from my laptop and run the app it crashes.

My logcat says that I am trying to call a null array... but it isn't null? I don't understand why when I run the app through Android Studio to my phone everything works fine but when I run it alone it crashes. Thankful for any help!

Here is my logcat

FATAL EXCEPTION: main
Process: com.example.abc.def, PID: 28693
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.abc.def/com.example.abc.def.MainActivity}: java.lang.NullPointerException: Attempt to read from null array
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3253)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3349)
at android.app.ActivityThread.access$1100(ActivityThread.java:221)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7224)
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 read from null array
at com.example.abc.def.MainActivity.onCreate(MainActivity.java:49)
at android.app.Activity.performCreate(Activity.java:6876)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1135)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3206)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3349) 
at android.app.ActivityThread.access$1100(ActivityThread.java:221) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:158) 
at android.app.ActivityThread.main(ActivityThread.java:7224) 
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)

And here is my code. The issue arises at the bottom when I call btn1.setText(itemArray[0]) because the array is "null"

public class MainActivity extends AppCompatActivity {

Button btn1, btn2;
String btn1Name, btn2Name;
String btnValue = "", itemValue = "", itemPosition = "";
String[] buttonArray = new String[]{"blank", "blank"};
String[] itemArray = new String[]{"blank", "blank"};
String[] positionArray = new String[]{"blank", "blank"};  

@Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    btn1 = (Button) findViewById(R.id.button1);
    btn2 = (Button) findViewById(R.id.button2);

    Bundle extras = getIntent().getExtras();
    if (extras != null) {
        btnValue = extras.getString("btnValue");
        itemValue = extras.getString("itemValue");
        itemPosition = extras.getString("itemPosition");

        buttonArray = extras.getStringArray("buttonArray");
        itemArray = extras.getStringArray("array");
        positionArray = extras.getStringArray("positionArray");

        if (btnValue != null && btnValue.equals("btn1")){
            buttonArray[0] = btnValue;
            itemArray[0] = itemValue;
            positionArray[0] = itemPosition;
        } else if (btnValue != null && btnValue.equals("btn2")) {
            buttonArray[1] = btnValue;
            itemArray[1] = itemValue;
            positionArray[1] = itemPosition;
        }
    }

    btn1.setText(itemArray[0]);
    btn2.setText(itemArray[1]);
}
}

What is being returned by "extras.getString("itemValue")" & "itemArray = extras.getStringArray("array");"? — Adeel Shahzad, Nov 25 '16 at 05:32
@AdeelShahzad it's from another activity. I don't think it would have anything to do with my code though since "extras" should be null when I launch the app. itemArray[0] and [1] is already assigned to "blank" at the launch of the activity. — Pam, Nov 25 '16 at 05:42
Can you please post the other class code where you are passing these extras? — Adeel Shahzad, Nov 25 '16 at 05:44
It's just my opinion that "extras.getStringArray("array");" is returning null. I can be wrong, though. Place a breakpoint on that statement and evaluate that expression — Adeel Shahzad, Nov 25 '16 at 06:08

score 1 · Accepted Answer · edited May 23 '17 at 12:30

I'm guessing here, but is MainActivity the first activity in the project?

I think you wrote the code to handle returning to this activity with data from other activities. I just tried and getIntent().getExtras() returns null when the activity is first created on an emulator. However, when I ran it on my device, getIntent generated this exception.

Note that onCreate is called once, so if you want to see the results of another activity, take a look at How to manage `startActivityForResult` on Android?.

Android - Null Array. Runs in Android Studio emulator but not on real device when unplugged

1 Answers1