NavigationBar滑动时自动隐藏，和twitter的效果一样。
向上滑动时，将会隐藏NavigationBar，隐藏后可显示更多的内容。向下滑动时，将会显示导航栏。
最重要的是pod STNavigationBarAutoHide 后，你仅需一句代码便可实现此功能。
[self st_navigationBarAutoHideConfigureScrollView:yourScrollView];
Demo效果
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实现思路
滑动隐藏navigationBar分为两部分，位置偏移及导航栏上内容透明度调整。
通过修改navigationBar的transform.ty实现位置偏移。
递归获取_UINavigationBarContentView的subviews，再更改其alpha，因导航标题无法更改alpha，便采用了修改titleTextAttributes中NSForegroundColorAttributeName的alpha来实现透明度调整。
实现细节
记录下开始拖动时的偏移量
- (void)st_scrollViewWillBeginDragging:(UIScrollView *)scrollView {
CGFloat contentOffsetY = scrollView.contentOffset.y + scrollView.adjustedContentInset.top;
[self st_setBeginContentOffsetY:contentOffsetY];
}
滑动时，判断是否隐藏
- (void)st_scrollViewDidScroll:(UIScrollView *)scrollView {
CGFloat contentOffsetY = scrollView.contentOffset.y + scrollView.adjustedContentInset.top;
//滑动距离，大于0时，向上滑动；小于0时，向下滑动。
CGFloat scrollOffsetY = contentOffsetY - [self st_beginContentOffsetY];
//导航栏高度
CGFloat navigationBarHeight = self.navigationController.navigationBar.frame.size.height;
//导航栏是否隐藏
bool navigationBarHidden = [self st_navigationBarHidden];
//向上滑动且导航未隐藏
if (scrollOffsetY > 0 && !navigationBarHidden) {
//滑动距离（下方用于计算动画进度）不大于导航高度
scrollOffsetY = MIN(navigationBarHeight, scrollOffsetY);
//滑动距离等于导航高度时，导航栏完全隐藏
if (scrollOffsetY == navigationBarHeight) {
[self st_setNavigationBarHidden:true];
[self st_setBeginContentOffsetY:contentOffsetY];
}
//计算动画进度，更改导航内容透明度
CGFloat alpha = (navigationBarHeight - scrollOffsetY) / navigationBarHeight;
[self updateNavigationBarAlpha:alpha];
//更改导航位置偏移量
self.navigationController.navigationBar.transform = CGAffineTransformMakeTranslation(0, -scrollOffsetY);
}
//向下滑动 并且 偏移量小于导航高度 并且 导航已隐藏时，显示导航
else if (scrollOffsetY < 0 && contentOffsetY < navigationBarHeight && navigationBarHidden) {
[self st_showNavigationBarWithAnimated:true];
}
}
拖动结束时，判断是否隐藏
- (void)st_scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset {
//速度
CGFloat velocityY = velocity.y;
//速度小于0时，向下拖动，显示导航栏
if (velocityY < 0) {
[self st_showNavigationBarWithAnimated:true];
}
//速度为0时
else if (velocityY == 0) {
CGFloat contentOffsetY = scrollView.contentOffset.y + scrollView.adjustedContentInset.top;
CGFloat scrollOffsetY = contentOffsetY - [self st_beginContentOffsetY];
CGFloat navigationBarHeight = self.navigationController.navigationBar.frame.size.height;
//偏移量小于导航高度时，显示导航栏
if (contentOffsetY < navigationBarHeight) {
[self st_showNavigationBarWithAnimated:true];
} else {
//导航当前位置偏移
CGFloat transformTy = self.navigationController.navigationBar.transform.ty;
//当导航已隐藏，或已显示时，return
if (transformTy == 0 && transformTy == -navigationBarHeight) return;
if (scrollOffsetY <= 0) return;
//处理向上拖动，导航未完全隐藏时，拖动结束情况
if (transformTy >= -navigationBarHeight / 2.0) {
[self st_showNavigationBarWithAnimated:true];
} else {
[self st_hideNavigationBarWithAnimated:true];
}
}
}
}
用category封装
新建UIViewController+NavigationBarAutoHide类
配置scrollView
- (void)st_navigationBarAutoHideConfigureScrollView:(UIScrollView *)scrollView {
if (scrollView == nil) {
NSLog(@"[ST NavigationBarAutoHide Error] scrollView cannot be nil!");
return;
}
if (self.navigationController == nil) {
NSLog(@"[ST NavigationBarAutoHide Error] self.navigationController cannot be nil!");
return;
}
if (scrollView.delegate == nil) {
scrollView.delegate = self;
}
//自动隐藏默认设为可用
[self st_setNavigationBarAutoHideEnabled:true];
//交换scrollView delegate上方用到的三个方法
[self st_swizzleScrollViewDelegateMethod];
}
交换scrollView delegate用到的三个方法
- (void)st_swizzleScrollViewDelegateMethod {
[self st_swizzleScrollViewMethodWithOriginalSelector:@selector(scrollViewDidScroll:) swizzleSelector:@selector(st_scrollViewDidScroll:)];
[self st_swizzleScrollViewMethodWithOriginalSelector:@selector(scrollViewWillBeginDragging:) swizzleSelector:@selector(st_scrollViewWillBeginDragging:)];
[self st_swizzleScrollViewMethodWithOriginalSelector:@selector(scrollViewWillEndDragging:withVelocity:targetContentOffset:) swizzleSelector:@selector(st_scrollViewWillEndDragging:withVelocity:targetContentOffset:)];
}
- (void)st_swizzleScrollViewMethodWithOriginalSelector:(SEL)originalSelector swizzleSelector:(SEL)swizzleSelector {
Method originalMethod = class_getInstanceMethod([self class], originalSelector);
Method swizzledMethod = class_getInstanceMethod([self class], swizzleSelector);
//若未实现代理方法，则先添加代理方法
BOOL didAddOriginalMethod = st_addMethod([self class], originalSelector, originalMethod);
BOOL didAddSwizzledMethod = st_addMethod([self class], swizzleSelector, swizzledMethod);
if (didAddOriginalMethod) {
Method newOriginalMethod = class_getInstanceMethod([self class], originalSelector);
if (originalMethod == newOriginalMethod) {
didAddOriginalMethod = false;
}
}
if (didAddSwizzledMethod) {
Method newSwizzledMethod = class_getInstanceMethod([self class], swizzleSelector);
if (swizzledMethod == newSwizzledMethod) {
didAddSwizzledMethod = false;
}
}
//如果两个方法都存在，则表示已交换过
if (!didAddOriginalMethod && !didAddSwizzledMethod) return;
st_swizzleSelector([self class], originalSelector, swizzleSelector);
}
static inline BOOL st_addMethod(Class theClass, SEL selector, Method method) {
return class_addMethod(theClass, selector, method_getImplementation(method), method_getTypeEncoding(method));
}
static inline void st_swizzleSelector(Class theClass, SEL originalSelector, SEL swizzledSelector) {
Method originalMethod = class_getInstanceMethod(theClass, originalSelector);
Method swizzledMethod = class_getInstanceMethod(theClass, swizzledSelector);
method_exchangeImplementations(originalMethod, swizzledMethod);
}
最后
更多细节可查看源码，STNavigationBarAutoHide，支持pod。
如果你有问题，可以在github上给我提Issue或者在下方评论。
如果此项目有帮助到你，请给我一个star。谢谢～