Calling Parent Form Public method in child Form

I have scenario I have a parent form which has a method M. If user clicks a button on Parent it opens a child form.In the child form if the user click 'ok' button i need to call a public method in parent form.Ppl around here are suggesting to use form run object which didnt wrk

i used two appoaches

1. {

object formrunobj;

formrunobj=args.caller();

formrunobj.M(); 

}

this approach didn't work.

2.I tried  to pass a string value args.parm() to parent form from child and basing on the string I am tried to run the method with if condition .It didn't work.

Please suggest me any ideas.If possible code example .Thanks in Advance.