ios - update content size of UIScrollView -

i have following code:

- (void) scrollviewdidenddecelerating:(uiscrollview *) scrollview { float currentendpoint = scrollview.contentoffset.y + scrollview.frame.size.height;  if (currentendpoint >= scrollview.contentsize.height) {     uiview *parent = [[uiview alloc] initwithframe:cgrectmake(5.0, 665.0, 310.0, 340.0)];     parent.backgroundcolor = [uicolor whitecolor];     parent.layer.cornerradius = 2.0;     parent.layer.bordercolor = [uicolor regularcolor].cgcolor;     parent.layer.borderwidth = 1.0f;      // increase size of content view     cgrect newcontentview = _contentview.frame;      newcontentview.size.width = _contentview.frame.size.width;     newcontentview.size.height = _contentview.frame.size.height + 340.0;      [_contentview setframe:newcontentview];      [_contentview addsubview:parent]; } 

but far scroll view doesn't it's updated content view.
how update content view here?

thanks.