iOS navigationBar和tabBar变透明 & navigationBar根据滑动距离的渐变色实现

转载自网友“tongyuling”
原博客地址 http://www.cnblogs.com/tongyuling/p/5822342.html

navigationBar变为纯透明

//第一种方法

//导航栏纯透明

[self.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];

//去掉导航栏底部的黑线

self.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;

}