[SOLVED]Android studio app crashing because of onClickListener

The eventlistener do not recognize the button object on witch it will be set just check if the button is declared with id and initialized (Button) = btn.findViewById(....) we can not help you if there is no full code.Else just research in stackoverflow or google the error message.

You have to see logcat for errors or to build your project synchronize gradle will sometimes helps.

Charlie Crease-huggett , Write code in code playground and then link it to your question. I can't see implementation of OnClickListener(). We'll need to see complete code. As suggested earlier also post messages from logcat. + Check if you have really added `android:id` attributes to views in xml file.

Did I not link the code correctly? Anyway your right I realized at that exact moment as you've messaged. I'm putting the code in the wrong class and it cannot find it within the layout... I'm sorry about that

HBhZ_C synced the gradle as recommended still not working. I have tried log.d but as soon as my app tries to get to the activity before it will crash before.

Yes just checked, the app works well when you set in XML , I just want to do it this way to re use activities, i.e. I don't want to create a separate activity for each mathematics subject I create

Just found this error message when running in debug mode. Does this help? E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.mathematics_educational, PID: 23508 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mathematics_educational/com.example.mathematics_educational.Sel_Chap}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference

[SOLVED] I had put the code into the wrong class which is why it could not find the correct button.

Thesmallest thanks for that nice to meet group standards. :)

Thanks for the advice, unfortunately it did not seem to work.

🇮🇳Omkar🕉 I checked the XML files they did all contain ids. I have attached my code, I did not realise it did not go through fully. I would be very appreciative if you could highlight my mistake as I've spent a considerable amount of time.