Q:UITableView scrollViewDidScroll function to change the custom navigationBar's alpha - ios

Question

In my view controller, I have a tableView, and I also add a custom navigationBar on my view controller's view, I want to fade the alpha of my custom navigationBar, but its appears no use, and I printed the alpha of my custom navigationBar, it shows alright, but my custom navigationBar look like no change on its alpha, this is my code:
#pragma mark -- scorllView delegate
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
if(scrollView == _tableview){
CGFloat currentOffsetY = scrollView.contentOffset.y;
// 0 ~ 358 -20 ~ 338
float alpha_of_scroll = (currentOffsetY + 20) / 358.0;
NSLog(#"%f", alpha_of_scroll);
_narBarView.alpha = 1 - alpha_of_scroll;
NSLog(#"%f", _narBarView.alpha);
}
}
By the way, I have tested use reactive cocoa, it shows alike to the scrollViewDidScroll function.

Answer 1

Try this:
- (void)viewDidLoad {
[super viewDidLoad];
UIView *overlay = [[UIView alloc] initWithFrame:CGRectMake(0, -20, CGRectGetWidth(self.navigationController.navigationBar.bounds), CGRectGetHeight(self.navigationController.navigationBar.bounds) + 20)];
overlay.userInteractionEnabled = NO;
overlay.backgroundColor = [UIColor orangeColor];
[self.navigationController.navigationBar insertSubview:overlay atIndex:0];
[self.navigationController.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];
}
#pragma mark -- scorllView delegate
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
if(scrollView == self.myTableView){
CGFloat offsetY = scrollView.contentOffset.y;
NSLog(#"%f", offsetY);
if (offsetY > -64) {
if (offsetY >= 0) {
[self setNavigationBarAlpha:0];
} else {
[self setNavigationBarAlpha:(-offsetY / 64)];
}
} else {
[self setNavigationBarAlpha:1];
}
}
}
- (void)setNavigationBarAlpha:(CGFloat)alpha {
[[self.navigationController.navigationBar subviews] enumerateObjectsUsingBlock:^(UIView *obj, NSUInteger idx, BOOL *stop) {
obj.alpha = alpha;
}];
}