What is the difference between android.support.v4.app.fragment and androidx.fragment.app.FragmentActivity

Question

apparently there is a X under import androidx.fragment.app.FragmentActivity , when I try to create a fragmentActivity. However, when I look for a sample project, it imports android.support.v4.app.fragment instead. May I know whats the difference, and why do I have this following error when I try to run my own project?:

java.lang.ClassCastException: com.fragmenttest.helloapp.ui.collection.ViewPagerIndicatorActivity cannot be cast to androidx.fragment.app.Fragment.

Answer 1

android.support.v4.app.fragment it's the package for the old Android support fragments.

androidx.fragment.app.FragmentActivity it's where the new fragments are. This came to replace the previous package because it's a much cleaner namespace. This is also known as Android X.

Probably the examples you're seeing are old and still use the old package. If I'm not mistaken Androidx was introduced 1 or 2 years ago.

In most cases you can simply replace the import, but I think the best way is to use Android Studio's migrate to Androidx

Answer 2

First of all you are using different libraries.

android.support.v4.app.* is included in the support libraries .
androidx.fragment.app.* is included in the androidx libraries .

They can't work together. Check the info to migrate .

Then an Activity (or subclasses) is not a Fragment .
You can't cast a Fragment in an Activity.

Answer 3

Activity != Fragment , your java.lang.ClassCastException is suggesting that you want to cast Fragment to Activity

Activity is full screen (mostly), Fragment is only a piece of look, kind of very extended View . One Activity can handle multiple Fragment s, eg on bigger screens .

FragmentActivity was introduced in support pack for handling all Fragment s features in lower OS versions, now you should use AppCompatActivity which extends FragmentActivity