You create an interface first, then define a method, which would act as a callback. In this example we would have two classes, one classA and another classB
Interface:
public interface OnCustomEventListener{
public void onEvent(); //method, which can have parameters
}
the listener itself in classB (we only set the listener in classB)
private OnCustomEventListener mListener; //listener field
//setting the listener
public void setCustomEventListener(OnCustomEventListener eventListener) {
this.mListener=eventListener;
}
in classA, how we start listening for whatever classB has to tell
classB.setCustomEventListener(new OnCustomEventListener(){
public void onEvent(){
//do whatever you want to do when the event is performed.
}
});
how do we trigger an event from classB (for example on button pressed)
if(this.mListener!=null){
this.mListener.onEvent();
}
P.S. Your custom listener may have as many parameters as you want