在我們?nèi)粘ｉ_發(fā)中，總有那么一兩個界面需要去隱藏導(dǎo)航欄，這時如何去合理的處理呢？筆者這里提供了幾個常用的方案和帶來的問題，并在最后給個筆者認(rèn)為較為優(yōu)雅的方法。

方案一：使用setNavigationBarHidden:animated:方法直接處理

- (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];
}

這個使我們解決隱藏導(dǎo)航欄首先會想到的方案，這種方式雖然很好的解決了，首頁隱藏導(dǎo)航欄，push到新界面不隱藏的場景。但如下場景會有個過度動畫，很難看：

• 1. 首頁需要隱藏，push的新界面也需要隱藏，這時就會有個隱藏--顯示--隱藏的過度動畫；
• 2. 首頁隱藏，然后在切換tabBar再回來，這時有一個導(dǎo)航欄向上消失的動畫；

所以這種直接使用的方案，不完美，pass。

方案二：使用UINavigationControllerDelegate代理方法直接處理

@interface HomePageController () <UINavigationControllerDelegate>
@end

@implementation HomePageController 

#pragma mark - lifeCycle
- (void)viewDidLoad {
    [super viewDidLoad];
    
    // 設(shè)置導(dǎo)航控制器的代理為self
    self.navigationController.delegate = self;
}

#pragma mark - < UINavigationControllerDelegate >

- (void)navigationController:(UINavigationController *)navigationController willShowViewController:(UIViewController *)viewController animated:(BOOL)animated {
    // 判斷要顯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;
}

通過當(dāng)前self對象來管理導(dǎo)航欄的顯示和隱藏，雖然能解決切換tabBar的動畫問題，但是還是沒有解決上面的問題1。

不完美，pass。

方案三：參考FDFullscreenPopGesture思路的實現(xiàn)方案，完美解決以上問題

主要的思路是使用runtime去hook UIViewController的viewWillAppear:方法和navigationController的pushViewController:animated:及setViewControllers:animated:方法實現(xiàn)。
相當(dāng)于是在每個UIViewController控制器，在調(diào)用viewWillAppear:方法的時候，都去判斷下是否需要隱藏導(dǎo)航欄setNavigationBarHidden:animated:方法，這樣的好處是，不用再當(dāng)前控制器的viewWillDisappear:中寫顯示方法，也就沒有了過渡的動畫問題，完美解決。

• 給UIViewController添加一個設(shè)置隱藏導(dǎo)航欄的屬性lsl_prefersNavigationBarHidden：

// MARK: - 給UIViewController添加lsl_prefersNavigationBarHidden屬性

@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，并在此方法中執(zhí)行已經(jīng)存好的代碼塊：

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

@interface UIViewController (HandlerNavigationBarPrivate)

@property(nonatomic, copy) _LSLViewControllerWillAppearInjectBlock lsl_willAppearInjectBlock;

@end

// MARK: - 替換UIViewController的viewWillAppear方法，在此方法中，執(zhí)行設(shè)置導(dǎo)航欄隱藏和顯示的代碼塊。
@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，當(dāng)控制器被壓入棧中的時候，預(yù)存設(shè)置隱藏和顯示導(dǎo)航欄的代碼塊到即將顯示的控制器中，備控制器調(diào)用：

// MARK: - 替換UINavigationController的pushViewController:animated:方法，在此方法中去設(shè)置導(dǎo)航欄的隱藏和顯示
@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<UIViewController *> *)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;
    }

    // 即將被調(diào)用的代碼塊
    __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];
        }
    };

    // 給即將顯示的控制器，注入代碼塊
    appearingViewController.lsl_willAppearInjectBlock = block;

    // 因為不是所有的都是通過push的方式，把控制器壓入stack中，也可能是"-setViewControllers:"的方式，所以需要對棧頂控制器做下判斷并賦值。
    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

方案三可以完美解決以上所遇見的問題，demo中有相應(yīng)的案例和完整代碼。