iOS开发-优雅的解决导航栏隐藏问题

在我们日常开发中，总有那么一两个界面需要去隐藏导航栏，这时如何去合理的处理呢？笔者这里提供了几个常用的方案和带来的问题，并在最后给个笔者认为较为优雅的方法。

方案一：使用setNavigationBarHidden:animated:方法直接处理

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];

    [self.navigationController setNavigationBarHidden:true animated:animated];
}

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    [self.navigationController setNavigationBarHidden:false animated:animated];
}

这个使我们解决隐藏导航栏首先会想到的方案，这种方式虽然很好的解决了，首页隐藏导航栏，push到新界面不隐藏的场景。但如下场景会有个过度动画，很难看：

• 1. 首页需要隐藏，push的新界面也需要隐藏，这时就会有个隐藏--显示--隐藏的过度动画；
• 2. 首页隐藏，然后在切换tabBar再回来，这时有一个导航栏向上消失的动画；

所以这种直接使用的方案，不完美，pass。

方案二：使用UINavigationControllerDelegate代理方法直接处理

@interface HomePageController () 
@end

@implementation HomePageController 

#pragma mark - lifeCycle
- (void)viewDidLoad {
    [super viewDidLoad];
    
    // 设置导航控制器的代理为self
    self.navigationController.delegate = self;
}

#pragma mark - < UINavigationControllerDelegate >

- (void)navigationController:(UINavigationController *)navigationController willShowViewController:(UIViewController *)viewController animated:(BOOL)animated {
    // 判断要显示的控制器是否是自己
    BOOL isShowHomePage = [viewController isKindOfClass:[self class]];
    
    [self.navigationController setNavigationBarHidden:isShowHomePage animated:YES];
}

- (void)dealloc {
    self.navigationController.delegate = nil;
}

通过当前self对象来管理导航栏的显示和隐藏，虽然能解决切换tabBar的动画问题，但是还是没有解决上面的问题1。

不完美，pass。

方案三：参考FDFullscreenPopGesture思路的实现方案，完美解决以上问题

主要的思路是使用runtime去hook UIViewController的viewWillAppear:方法和navigationController的pushViewController:animated:及setViewControllers:animated:方法实现。
相当于是在每个UIViewController控制器，在调用viewWillAppear:方法的时候，都去判断下是否需要隐藏导航栏setNavigationBarHidden:animated:方法，这样的好处是，不用再当前控制器的viewWillDisappear:中写显示方法，也就没有了过渡的动画问题，完美解决。

• 给UIViewController添加一个设置隐藏导航栏的属性lsl_prefersNavigationBarHidden：

// MARK: - 给UIViewController添加lsl_prefersNavigationBarHidden属性

@implementation UIViewController (HandlerNavigationBar)

- (BOOL)lsl_prefersNavigationBarHidden
{
    return [objc_getAssociatedObject(self, _cmd) boolValue];
}

- (void)setLsl_prefersNavigationBarHidden:(BOOL)hidden
{
    objc_setAssociatedObject(self, @selector(lsl_prefersNavigationBarHidden), @(hidden), OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

@end

• hook UIViewController的viewWillAppear:方法，并在此方法中执行已经存好的代码块：

typedef void(^_LSLViewControllerWillAppearInjectBlock)(UIViewController *viewController, BOOL animated);

@interface UIViewController (HandlerNavigationBarPrivate)

@property(nonatomic, copy) _LSLViewControllerWillAppearInjectBlock lsl_willAppearInjectBlock;

@end

// MARK: - 替换UIViewController的viewWillAppear方法，在此方法中，执行设置导航栏隐藏和显示的代码块。
@implementation UIViewController (HandlerNavigationBarPrivate)

+ (void)load
{
    Method orginalMethod = class_getInstanceMethod(self, @selector(viewWillAppear:));
    Method swizzledMethod = class_getInstanceMethod(self, @selector(lsl_viewWillAppear:));
    method_exchangeImplementations(orginalMethod, swizzledMethod);
}

- (void)lsl_viewWillAppear:(BOOL)animated
{
    [self lsl_viewWillAppear:animated];

    if (self.lsl_willAppearInjectBlock) {
        self.lsl_willAppearInjectBlock(self, animated);
    }
}

- (_LSLViewControllerWillAppearInjectBlock)lsl_willAppearInjectBlock
{
    return objc_getAssociatedObject(self, _cmd);
}

- (void)setLsl_willAppearInjectBlock:(_LSLViewControllerWillAppearInjectBlock)block
{
    objc_setAssociatedObject(self, @selector(lsl_willAppearInjectBlock), block, OBJC_ASSOCIATION_COPY_NONATOMIC);
}

@end

• hook住navigationController的pushViewController:animated:及setViewControllers:animated:方法，当控制器被压入栈中的时候，预存设置隐藏和显示导航栏的代码块到即将显示的控制器中，备控制器调用：

// MARK: - 替换UINavigationController的pushViewController:animated:方法，在此方法中去设置导航栏的隐藏和显示
@implementation UINavigationController (NavigationBar)

+ (void)load
{
    Method originMethod = class_getInstanceMethod(self, @selector(pushViewController:animated:));
    Method swizzedMethod = class_getInstanceMethod(self, @selector(lsl_pushViewController:animated:));
    method_exchangeImplementations(originMethod, swizzedMethod);

    Method originSetViewControllersMethod = class_getInstanceMethod(self, @selector(setViewControllers:animated:));
    Method swizzedSetViewControllersMethod = class_getInstanceMethod(self, @selector(lsl_setViewControllers:animated:));
    method_exchangeImplementations(originSetViewControllersMethod, swizzedSetViewControllersMethod);
}

- (void)lsl_pushViewController:(UIViewController *)viewController animated:(BOOL)animated
{
    // Handle perferred navigation bar appearance.
    [self lsl_setupViewControllerBasedNavigationBarAppearanceIfNeeded:viewController];

    // Forward to primary implementation.
    [self lsl_pushViewController:viewController animated:animated];
}

- (void)lsl_setViewControllers:(NSArray *)viewControllers animated:(BOOL)animated
{
    // Handle perferred navigation bar appearance.
    for (UIViewController *viewController in viewControllers) {
        [self lsl_setupViewControllerBasedNavigationBarAppearanceIfNeeded:viewController];
    }

    // Forward to primary implementation.
    [self lsl_setViewControllers:viewControllers animated:animated];
}

- (void)lsl_setupViewControllerBasedNavigationBarAppearanceIfNeeded:(UIViewController *)appearingViewController
{
    if (!self.lsl_viewControllerBasedNavigationBarAppearanceEnabled) {
        return;
    }

    // 即将被调用的代码块
    __weak typeof(self) weakSelf = self;
    _LSLViewControllerWillAppearInjectBlock block = ^(UIViewController *viewController, BOOL animated){
        __strong typeof(weakSelf) strongSelf = weakSelf;
        if (strongSelf) {
            [strongSelf setNavigationBarHidden:viewController.lsl_prefersNavigationBarHidden animated:animated];
        }
    };

    // 给即将显示的控制器，注入代码块
    appearingViewController.lsl_willAppearInjectBlock = block;

    // 因为不是所有的都是通过push的方式，把控制器压入stack中，也可能是"-setViewControllers:"的方式，所以需要对栈顶控制器做下判断并赋值。
    UIViewController *disappearingViewController = self.viewControllers.lastObject;
    if (disappearingViewController && !disappearingViewController.lsl_willAppearInjectBlock) {
        disappearingViewController.lsl_willAppearInjectBlock = block;
    }
}

- (BOOL)lsl_viewControllerBasedNavigationBarAppearanceEnabled
{
    NSNumber *number = objc_getAssociatedObject(self, _cmd);
    if (number) {
        return number.boolValue;
    }
    self.lsl_viewControllerBasedNavigationBarAppearanceEnabled = YES;
    return YES;
}

- (void)setLsl_viewControllerBasedNavigationBarAppearanceEnabled:(BOOL)enabled
{
    SEL key = @selector(lsl_viewControllerBasedNavigationBarAppearanceEnabled);
    objc_setAssociatedObject(self, key, @(enabled), OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

@end

方案三可以完美解决以上所遇见的问题，demo中有相应的案例和完整代码。