xcode - ScrollView jumps to top after setContentSize -

i have scrollview views. set elements hidden on button click. problem scrollview jumps top (0,0) on reset contentsize of scrollview. set scrollview content size follows:

if(![subview ishidden]){       scrollviewheight += subviewframe.size.height; }  [scrollview setcontentsize:(cgsizemake(320, scrollviewheight + 20))]; 

yes ,whenever changing content size automatically contentoffset value taken (0,0).after changing frame can set contentoffset value related newly generated scrollview frame.