scrollView滚动导航条渐变

很多时候项目中要求导航栏的颜色随着scrollview的滚动发生渐变,于是自己就写了一个demo没方法比较简单写一个UINavigationBar的分类在分类的.h文件中声明两个方法

#import@interface UINavigationBar (LH)

- (void)lhSetBackgroundColor:(UIColor *)backgroundColor;

- (void)lhReset;

@end

在.m文件中实现方法其中需要注意的是用到了runtime的关联对象 ,关联对象就是把两个对象相互关联起来,使得一个对象多为另一个对象的一部分.具体讲解以后会给大家以文章形式写出来 ,这里就不过多讲解了

#import@implementation UINavigationBar (LH)

static char overlayKey;

- (UIView *)overlay{

return objc_getAssociatedObject(self, &overlayKey);

}

- (void)setOverlay:(UIView *)overlay{

objc_setAssociatedObject(self, &overlayKey, overlay, OBJC_ASSOCIATION_RETAIN_NONATOMIC);

}

- (void)lhSetBackgroundColor:(UIColor *)backgroundColor{

if (!self.overlay) {

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

self.overlay = [[UIView alloc] initWithFrame:CGRectMake(0, -20, [UIScreen mainScreen].bounds.size.width, CGRectGetHeight(self.bounds)+20)];

self.overlay.userInteractionEnabled = NO;

self.overlay.autoresizingMask = UIViewAutoresizingFlexibleWidth;

[self insertSubview:self.overlay atIndex:0];

}

self.overlay.backgroundColor = backgroundColor;

}

- (void)lhReset{

[self setBackgroundImage:nil forBarMetrics:UIBarMetricsDefault];

[self.overlay removeFromSuperview];

self.overlay = nil;

}

@end

现在是只要在你要实现的控制器中调用这连个方法就好了其中最主要的方法就是

#pragma mark UIScrollViewDelegate

- (void)scrollViewDidScroll:(UIScrollView *)scrollView

{

UIColor *color = [UIColor colorWithRed:45/255.0 green:45/255.0 blue:45/255.0 alpha:1];

CGFloat offsetY = scrollView.contentOffset.y;

if (offsetY >= - self.view.frame.size.height ) {

CGFloat alpha = 1- offsetY/self.view.frame.size.height;

[self.navigationController.navigationBar lhSetBackgroundColor:[color colorWithAlphaComponent:alpha]];

self.titlelabel.alpha = alpha;

} else {

[self.navigationController.navigationBar lhSetBackgroundColor:[color colorWithAlphaComponent:0]];

}

当然不会忘了demo的连接的:https://git.oschina.net/huanni/scrollviewNav.git

效果图如下