Android SDK error: Trying instantiate a class that is not a fragment

Question

I am hardly trying to create a simple application with a top menu and a changeable view below (by pressing the buttons in the menu fragment we change the view of the fragment be

Answer 1

You should be using FragmentActivity instead of Activity that is because you are using support Fragments and multiple Fragments in your activity main

---

Edit

You can now use the Appcompat support library and extends AppCompatActivity to support toolbar and fragment for lower api.

Answer 2

In my case it turned out, I was doing stuff in onCreate in the wrong order:

setContentView(R.layout.activity_qr_code_scan);
super.onCreate(savedInstanceState);

instead of

super.onCreate(savedInstanceState);
setContentView(R.layout.activity_qr_code_scan);

Answer 3

As you are using fragments in your layout and I suggest you to extend your class from fragment or fragment activity.