java - Android - How to display Backstack Fragment -

when btn clicked fragment 1 displayed, when press btn2 fragment 2 displayed , believe fragment 1 placed in backstack. second time around, when clicked btn, wanted display previous state. i'll include code made me confused , not sure how it.

btn.setonclicklistener(new view.onclicklistener() { public void onclick(view v) { string str = "frag1"; fragment videofragment = new videoplayerfragment(); fragmenttransaction transaction = getchildfragmentmanager().begintransaction(); transaction.replace(r.id.child_fragment, videofragment, str); transaction.addtobackstack(null); transaction.commit();  } });  btn2.setonclicklistener(new view.onclicklistener() { public void onclick(view v) { string str2 ="frag1"; string str3 ="frag2"; //fragmentmanager.backstackentry backentry= //getfragmentmanager().getbackstackentryat(getactivity().getfragmentmanager(). //getbackstackentrycount()-1); //string str3 = backentry.getname(); //fragment fragment= getfragmentmanager().findfragmentbytag(str3);  fragment videofragment = new copyofvideoplayerfragment(); fragmenttransaction transaction2 = getfragmentmanager().begintransaction(); transaction2.addtobackstack(str2); transaction2.replace(r.id.child_fragment, videofragment, str3); transaction2.commit();  } }); 

confusing code , not working:

fragmentmanager.backstackentry backentry=getfragmentmanager().getbackstackentryat(getactivity().getfragmentmanager().getbackstackentrycount()-1); string str3 = backentry.getname(); fragment fragment= getfragmentmanager().findfragmentbytag(str3); 

for displaying previous fragtment (the 1 in backstack) , use code:

getsupportfragmentmanager().executependingtransaction();