My First App crashes when pressing a button

Question

I tried numerous times to make the app from the MyFirstApp Tutorial on developers.android (https://developer.android.com/training/basics/firstapp/index.html) work. I\'m test

Answer 1

your problem is here (DisplayMessageActivity):

@Override
protected void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);

   Intent intent = getIntent();
   String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);

   TextView textView = new TextView(this);
   textView.setTextSize(40);
   textView.setText(message);      
   setContentView(textView);

   if (savedInstanceState == null) {
       getSupportFragmentManager().beginTransaction()
              .add(R.id.container, new PlaceholderFragment()).commit();
   }
}

you are trying to add the Fragment to R.id.container which is not part of the Activity's view hierarchy, since the only thing that it contains is a TextView