How to get around NullPointerException when working with ActionBar?

Question

Android

Applications are developed for APIs >= 15.
As activities are used by AppCompatActivity, fragments are common.
When working with the ActionBar (whether it's setting text, a back button, icons, etc.), a warning about a possible NullPointerException always pops up, and when the application starts, it crashes.
Neither getActionBar() nor getSupportActionBar() works, a warning pops up in both cases.
I went around a bunch of questions on the topic and a normal solution was not found. There were all sorts of debug versions where, using the toolbar and setSupportActionBar(), something came out, but in the end I still had to catch NullPointerException, which is not at all happy.
Even just to add an icon, I had to create separate styles for the ActionBar, which is in no way convenient, given the existence of special methods for this.
Perhaps someone knows a working formula to solve the problem?

Answer 1

Most likely in your styles.xml file your main theme looks something like this:
The key point is NoActionBar. Here you need to use the Toolbar, place it yourself in the layouts, and call the setSupportActionBar(toolbar) method in the Activity

Answer 2

Do you have the NoActionBar theme installed?