iOS导航栏透明平滑过渡的简单实现
前言
项目中有时候需要某些导航栏看起来是透明的，但上面的item按钮还是存在的，那么要怎么比较快速又简单的实现呢？今天就来做个尝试，供大家参考, 这里介绍是导航栏的测滑，UIScrollView的滑动导航栏渐变也是一样的道理，监听滑动改变透明度即可。
导航栏透明
最简单的导航栏透明只要这几行代码就可以实现
navigationController?.navigationBar.setBackgroundImage(UIImage(), for: .default)
navigationController?.navigationBar.shadowImage = UIImage()
如果要取消透明，也很简单
navigationController?.navigationBar.setBackgroundImage(nil, for: .default)
navigationController?.navigationBar.shadowImage = nil
还有种手动发改变透明度的方式
extension UINavigationController{
func setBackgroundAlpha(alpha:CGFloat){
if let barBackgroundView = navigationBar.subviews.first{
if #available(iOS 11.0, *){
if navigationBar.isTranslucent{
for view in barBackgroundView.subviews {
view.alpha = alpha
}
}else{
barBackgroundView.alpha = alpha
}
} else {
barBackgroundView.alpha = alpha
}
}
}
}
这里可以给控制器添加属性方便直接修改
private var navBarAlpha: Void?
extension UIViewController{
// navigationBar _UIBarBackground alpha
var navBarBackgroundAlpha:CGFloat {
get {
guard let barBackgroundAlpha = objc_getAssociatedObject(self, &navBarAlpha) as? CGFloat else {
return 1.0
}
return barBackgroundAlpha
}
set {
objc_setAssociatedObject(self, &navBarAlpha, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
navigationController?.setBackgroundAlpha(alpha: newValue)
}
}
}
完成之后看起开是这样子的
image
好了，透明的方式介绍完了，现在开始如何正确的使用(runtime魔法)
runtime处理UIViewController的导航栏透明
如果简单的处理就是在需要透明的UIViewController中添加如下代码即可:
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
//在这里处理透明
navigationController?.navigationBar.setBackgroundImage(UIImage(), for: .default)
navigationController?.navigationBar.shadowImage = UIImage()
}
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
navigationController?.navigationBar.setBackgroundImage(nil, for: .default)
navigationController?.navigationBar.shadowImage = nil
}
每次如果都要这么写估计要疯，所以我们用runtime交换方法的实现来统一进行处理, 这里需要知道swift下如何进行swizzle method的方式, 详细请看我的另一篇文章
交换viewwillappear的实现
extension UIViewController{
func navigationBarTransparency() {
navigationController?.navigationBar.setBackgroundImage(UIImage(), for: .default)
navigationController?.navigationBar.shadowImage = UIImage()
}
func navigationBarUnTransparency() {
navigationController?.navigationBar.setBackgroundImage(nil, for: .default)
navigationController?.navigationBar.shadowImage = nil
}
public static func hook(){
///此方法的实现见 “swift下使用runtime交换方法的实现” 文章
DispatchQueue.once(token: onceToken)
{
let needSwizzleSelectorArr = [
#selector(viewWillAppear(_:))
]
for selector in needSwizzleSelectorArr {
let str = ("prefix_" + selector.description)
if let originalMethod = class_getInstanceMethod(self, selector),
let swizzledMethod = class_getInstanceMethod(self, Selector(str)) {
method_exchangeImplementations(originalMethod, swizzledMethod)
}
}
}
}
@objc private func prefix_viewWillAppear(_ animated: Bool) {
//调用系统的
prefix_viewWillAppear(animated)
updateNavAlpha()
}
//抽出需要透明的控制器方法
/// 需要导航栏透明的控制器
///
/// - Returns: bool
fileprivate func needOpacity() -> Bool{
return self.isKind(of: OneViewController.self) ||
self.isKind(of: TwoViewController.self)
}
private func updateNavAlpha() {
if needOpacity(){
navBarBackgroundAlpha = 0.0
}else{
navBarBackgroundAlpha = 1.0
}
}
}
这样控制各种需要透明的控制器就比较方便了。
监听手势的滑动改变导航栏的透明度（平滑的过渡）
这里只要交换导航控制的 _updateInteractiveTransition:就能实现
extension UINavigationController{
public static func injectHook()
guard self === UINavigationController.self else { return }
DispatchQueue.once(token: "com.moglo.hallo.UINavigationController") {
swizzle()
}
}
private static func swizzle(){
let needSwizzleSelectorArr = [
NSSelectorFromString("_updateInteractiveTransition:")
]
for selector in needSwizzleSelectorArr {
let str = ("prefix_" + selector.description)
if let originalMethod = class_getInstanceMethod(self, selector),
let swizzledMethod = class_getInstanceMethod(self, Selector(str)) {
method_exchangeImplementations(originalMethod, swizzledMethod)
}
}
}
@objc private func prefix_updateInteractiveTransition(_ percentComplete: CGFloat){
prefix_updateInteractiveTransition(percentComplete)
if let topVc = topViewController{
let fromAlpha = topVc.transitionCoordinator?.viewController(forKey: .from)?.navBarBackgroundAlpha ?? 1.0
let toAlpha = topVc.transitionCoordinator?.viewController(forKey: .to)?.navBarBackgroundAlpha ?? 0.0
let nowAlpha = fromAlpha + (toAlpha - fromAlpha) * percentComplete
// Console.debug("----------fromAlpha:\(fromAlpha) -- toAlpha:\(toAlpha) -- nowAlpha:\(nowAlpha)")
setBackgroundAlpha(alpha: nowAlpha)
}
}
}
此刻用手滑动可能会发现这样的问题
问题
这是由于控制器没有在导航栏下导致到的效果，其实就是属性extendedLayoutIncludesOpaqueBars作祟
只要在不需要透明的控制器中设置
extendedLayoutIncludesOpaqueBars = true
改造下刚才的方法
private func updateNavAlpha() {
if needOpacity(){
navBarBackgroundAlpha = 0.0
}else{
extendedLayoutIncludesOpaqueBars = true
navBarBackgroundAlpha = 1.0
}
}
到这里大致能实现完整需求了，看起来大概是这个样子
image
修复小瑕疵
1
因为是在viewwillappear中设置导航栏的透明度，所以push到下一个控制器的时候中间的跳变是比较明显的，
简单的做法就是, 做个动画让透明度的变化不是直接跳变
UIView.animate(withDuration: 0.25, animations: {
self.navgationBarAlpha = 0.0
}) { (finished) in
}
如果这么做，导航栏的底部黑线的隐藏方式不能像网上一直认为的写法
navigationBar.clipsToBounds = alpha == 0
所以这里介绍正确的隐藏方式
extension UINavigationController{
var hairLineView: UIImageView? {
get {
return objc_getAssociatedObject(self, &hairLine) as? UIImageView
}
set {
objc_setAssociatedObject(self, &hairLine, newValue, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
}
}
///查找分割线
public func findHairLine(view: UIView) -> UIImageView?{
if view.isKind(of: UIImageView.self) && view.frame.size.height <= 1.0{
return view as? UIImageView
}
for subView in view.subviews {
let imageView = findHairLine(view: subView)
if let imageView = imageView{
return imageView
}
}
return nil
}
public func setHairLine(hidden: Bool){
if let hairLineView = hairLineView{
hairLineView.isHidden = hidden
}else{
hairLineView = findHairLine(view: navigationBar)
hairLineView?.isHidden = hidden
}
}
}
在上述的setBackgroundAlpha变成
func setBackgroundAlpha(alpha:CGFloat){
if let barBackgroundView = navigationBar.subviews.first{
if #available(iOS 11.0, *){
if navigationBar.isTranslucent{
for view in barBackgroundView.subviews {
view.alpha = alpha
}
}else{
barBackgroundView.alpha = alpha
}
} else {
barBackgroundView.alpha = alpha
}
}
let hidden = alpha == 0
setHairLine(hidden: hidden)
}
2
在手势滑动过程中可能产生的小跳变解决
extension UINavgationController: UInavigationControllerDelegate{
public func navigationController(_ navigationController: UINavigationController, willShow viewController: UIViewController, animated: Bool) {
if let topVC = topViewController,
let coor = topVC.transitionCoordinator, coor.initiallyInteractive {
if #available(iOS 10.0, *) {
coor.notifyWhenInteractionChanges({[weak self] (context) in
self?.dealInteractionChanges(context)
})
} else {
coor.notifyWhenInteractionEnds({[weak self] (context) in
self?.dealInteractionChanges(context)
})
}
}
}
private func dealInteractionChanges(_ context: UIViewControllerTransitionCoordinatorContext){
if context.isCancelled{
let cancelDuration = context.transitionDuration * TimeInterval(context.percentComplete)
let fromVc = context.viewController(forKey: .from)
let nowAlpha = fromVc?.navBarBackgroundAlpha ?? 1.0
UIView.animate(withDuration: cancelDuration) {[weak self] in
self?.setBackgroundAlpha(alpha: nowAlpha)
}
}else{
let finishDuration = context.transitionDuration * TimeInterval(1 - context.percentComplete)
UIView.animate(withDuration: finishDuration) {[weak self] in
let nowAlpha = context.viewController(forKey: .to)?.navBarBackgroundAlpha ?? 1.0
self?.setBackgroundAlpha(alpha: nowAlpha)
}
}
}
}
这里是最终的效果
最终效果
总结
这是自己的一次尝试导航栏隐藏的总结，记录下踩过的坑，最后发个写的比较完全且比较牛的方案的链接
