SpringIndicator | A spring indicator like Morning Routine guide

Change build.gradle to -> dependencies {

implementation 'com.android.support:appcompat-v7:27.1.1'

implementation 'com.android.support.constraint:constraint-layout:1.1.0'

}

Try this.

Make foldersModelArrayList non static.

Initialize it inside onCreate().

Firstly, well done for writing a detailed description of the problem. Many questioners on StackOverflow can learn from the ability of this question to articulate the problem.

This error would seem to come from not accounting for Fragment lifecycle changes. While inside a ViewPager, Fragments will pass through various states including hidden and shown when they are temporarily offscreen, and paused and resumed if they are offscreen and the system frees memory, and finally created and destroyed if the Android system decides to save the instance state of your Activity (such as from a configuration change). In the latter case, Android will try and restore the state of your Fragments from saved instance state in your ViewPager. Since your Fragments have no way to save the View.OnClickedListener they were passed in the arguments, they end up with a null pointer when they are restored which is causing your error.

To fix the error, I suggest that you do not pass the View.OnClickedListener as a parameter to the Fragments. Rather, expose the OnClickListener to your Fragments via a public method in your Activity and have the Fragments get it themselves in their onResume(). This way you can guarantee that the Fragments will have a reference to the View.OnClickedListener whenever they are in a resumed state. So your onResume() might look something like this: