Android - Can't find the reason for NullPointerException

Question

I am trying to integrate Sinch video calling into my app, so I just copied all those Activities and Layouts from the Sinch Video-Call Demo App and it worked fine. Now I am trying to remove the LoginActivity so that a call establishes using a default, hard-coded userName instead of getting it from an EditText. And I only made changes to the LoginActivity.java and login.xml layout files.

But now, as soon as that Activity launches, it crashes with this error.

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.yankee.cw/com.example.yankee.cw.LoginActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setEnabled(boolean)' on a null object reference
                                                                           at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2462)
                                                                           at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2522)
                                                                           at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                                           at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1363)
                                                                           at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                           at android.os.Looper.loop(Looper.java:148)
                                                                           at android.app.ActivityThread.main(ActivityThread.java:5471)
                                                                           at java.lang.reflect.Method.invoke(Native Method)
                                                                           at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                                        Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setEnabled(boolean)' on a null object reference  

But nowhere in the whole code there is a setEnabled called on any Button object. Here is a link to the original layout file login.xml. And here is mine login.xml. OriginalLoginActivity.java and mine LoginActivity.java

I am sorry this might seem like a stupid question but I have tried everything I could in the code for the last 5 hours and I still couldn't find what is causing the problem because there is no call to setEnabled anywhere in the entire code. Thank you.

Answer 1

After reading your modifications and the base repository of the project in question I think the reason for the NullPointerException is the following:

After starting your LoginActivity it immediately follows the execution with LoginActivity#loginClicked() which starts the next activity rights away

private void openPlaceCallActivity() {
    Intent mainActivity = new Intent(this, PlaceCallActivity.class);
    startActivity(mainActivity);
}

... at android.app.ActivityThread.performLaunchActivity ...

The PlaceCallActivity extends BaseActivity which modifies the service lifecycle thus maybe calling the PlaceCallActivity#onServiceConnected before PlaceCallActivity#onCreate... which coincidentally may have a not initialized mCallButton

PlaceCallActivity#onServiceConnected

    @Override
        protected void onServiceConnected() {
            TextView userName = (TextView) findViewById(R.id.loggedInName);
            userName.setText(getSinchServiceInterface().getUserName());
            mCallButton.setEnabled(true);  // <--- might try changing this?
        }