动态修改UINavigationBar的背景色







- (void)scrollViewDidScroll:(UIScrollView *)scrollView

{
    UIColor *color = [UIColor blueColor];
    CGFloat offsetY = scrollView.contentOffset.y;
    if  (offsetY > 0) {
        CGFloat alpha = 1 - ((64 - offsetY) / 64);
        self.navigationController.navigationBar.backgroundColor = [color colorWithAlphaComponent:alpha];
    }  else  {
         self.navigationController.navigationBar.backgroundColor = [color colorWithAlphaComponent:0];
    }
}