How to call a method in MainActivity from another class?

Question

How do I call the method startChronometer in another class when the method is declared inside the main activity?

Inside MainActivity:

public void startChronometer() {
    mChronometer.start();
    showElapsedTime();
}

Inside another class, I tried to do this:

MainActivity mActivity;
mActivity.startChronometer();

But an error occurred which said:

java.lang.NullPointerException. 

May I know what more I need to add to the code?

Answer 1

You can easily call a method from any Fragment inside your Activity by doing a cast like this:

Java

((MainActivity)getActivity()).startChronometer();

Kotlin

(activity as MainActivity).startChronometer()

Just remember to make sure this Fragment's activity is in fact MainActivity before you do it.

Hope this helps!