本人最开始实现的方法是在视图即将显现的方法里面添加隐藏navigationBar，然后
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
self.navigationController.navigationBar.hidden=NO;
CGFloat offsetY = self.scrollView.contentOffset.y;
self.navigationController.navigationBar.alpha = offsetY/100;
}
这样写纯粹是取巧了 效果是// 先是纯透明 然后逐渐显示。
后面学习的方法：
navigationBar变为纯透明
//第一种方法
//导航栏纯透明
[self.navigationController.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];
//去掉导航栏底部的黑线
self.navigationController.navigationBar.shadowImage = [UIImage new];
//第二种方法
[[self.navigationBar subviews] objectAtIndex:0].alpha = 0;
tabBar同理
[self.tabBar setBackgroundImage:[UIImage new]];
self.tabBar.shadowImage = [UIImage new];
navigationBar根据滑动距离的渐变色实现
//第一种
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
CGFloat offsetToShow = 200.0;//滑动多少就完全显示
CGFloat alpha = 1 - (offsetToShow - scrollView.contentOffset.y) / offsetToShow;
[[self.navigationController.navigationBar subviews] objectAtIndex:0].alpha = alpha;
}
//第二种
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
CGFloat offsetToShow = 200.0;
CGFloat alpha = 1 - (offsetToShow - scrollView.contentOffset.y) / offsetToShow;
[self.navigationController.navigationBar setShadowImage:[UIImage new]];
[self.navigationController.navigationBar
setBackgroundImage:[self imageWithColor:[[UIColor
orangeColor]colorWithAlphaComponent:alpha]]
forBarMetrics:UIBarMetricsDefault];
}
//生成一张纯色的图片
- (UIImage *)imageWithColor:(UIColor *)color
{
CGRect rect = CGRectMake(0.0f, 0.0f, 1.0f, 1.0f);
UIGraphicsBeginImageContext(rect.size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(context, [color CGColor]);
CGContextFillRect(context, rect);
UIImage *theImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return theImage;
}
