ViewWillAppear 中的导航栏着色在 iOS 10 中发生得太晚了

Question

我遇到了一个奇怪的错误，它只发生在 iOS 10 上。

我有一个包含多个屏幕的应用程序，每个屏幕都为viewWillAppear 中的navigationBar 着色。因此，当您转到下一个屏幕时，它将正确着色。

但是，在 iOS 10 上进行测试时，我突然在返回上一个屏幕时看到以下行为： 当上一个屏幕出现时，navigationBar 仍然具有上一个屏幕的颜色，然后闪烁到正确的颜色。 它几乎看起来像 viewWillAppear 在某种程度上表现得像 viewDidAppear。

相关代码：

视图控制器：

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    [ViewControllerPainter paint:self withBackground:[UIColor whiteColor] andForeground:[UIColor blackColor] andIsLight:true];

}

画家：

+ (void)paint:(UIViewController *)controller withBackground:(UIColor *)backgroundColor andForeground:(UIColor *)foregroundColor andIsLight:(bool)isLight
{
    controller.navigationController.navigationBar.opaque = true;
    controller.navigationController.navigationBar.translucent = false;
    controller.navigationController.navigationBar.tintColor = foregroundColor;
    controller.navigationController.navigationBar.barTintColor = backgroundColor;
    controller.navigationController.navigationBar.backgroundColor = backgroundColor;
    controller.navigationController.navigationBar.barStyle = isLight ? UIBarStyleDefault : UIBarStyleBlack;
    controller.navigationController.navigationBar.titleTextAttributes = @{NSForegroundColorAttributeName: foregroundColor};
}

这是一个错误吗？我能做些什么来解决这个问题吗？这很令人沮丧。

Answer 1

以下是根据iOS 10 SDK Release Notes 更改的内容：

在 iOS 10 中，UIKit 更新并统一了 UINavigationBar、UITabBar 和 UIToolbar 的后台管理。特别是，更改这些视图的背景属性（例如背景或阴影图像，或设置栏样式）可能会启动栏的布局传递，以解决新的背景外观。
特别是，这意味着尝试更改 -[UIView layoutSubviews]、-[UIView updateConstraints]、-[UIViewController willLayoutSubviews]、-[UIViewController didLayoutSubviews]、-[UIViewController updateViewConstraints] 或任何其他内部的这些栏的背景外观响应布局调用的方法可能会导致布局循环。

所以问题似乎是viewWillAppear 正在触发上述布局循环，因为它是由于布局更改而被调用的：

对我来说，快速解决方法是覆盖 popViewControllerAnimated 和 pushViewController 并更新我的 UINavigationController 子类的 navigationBar 背景。下面是它的样子：

override func popViewControllerAnimated(animated: Bool) -> UIViewController? {
    let poppedViewController = super.popViewControllerAnimated(animated)

    // Updates the navigation bar appearance
    updateAppearanceForViewController(nextViewController)

    return poppedViewController
}

override func pushViewController(viewController: UIViewController, animated: Bool) {
    super.pushViewController(viewController, animated: animated)

    // Updates the navigation bar appearance
    updateAppearanceForViewController(viewController)
}

我的猜测是它可以工作，因为操作系统不会调用 popViewControllerAnimated 和 pushViewController 作为布局更改的结果，而是通过触摸事件调用。因此，如果您想找到另一个地方来更新您的 navigationBar 背景，请记住这一点。

Answer 2

我必须解决这个问题：

self.navigationController.navigationBarHidden = YES;
self.navigationController.navigationBarHidden = NO;

这样您就不必重写 popviewcontroller 或 pushviewcontroller。它基本上是触发导航栏重绘。

他们怎么能推出一个新版本的操作系统来破坏这么重要的东西，这仍然很烦人。

Answer 3

尝试使用willMoveToParentViewController，效果与覆盖UINavigationController 方法相同，但没有麻烦。

Answer 4

我正在发布 Objective-C（UINavigationController 的子类）的解决方案：

#import "FUINavigationController.h"

@interface FUINavigationController ()

@end

@implementation FUINavigationController

- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@"current: %@",[self.topViewController class]);

    if ([NSStringFromClass([self.topViewController class]) isEqualToString:@"LoginVC"]) {
        [self setNavBarHidden];
    }

    // Do any additional setup after loading the view.
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
-(UIViewController*)popViewControllerAnimated:(BOOL)animated {

    UIViewController *popedVC = [super popViewControllerAnimated:animated];

    if ([NSStringFromClass([popedVC class]) isEqualToString:@"SignUpVC"] && [NSStringFromClass([[super topViewController] class]) isEqualToString:@"LoginVC"]) {
        [self setNavBarHidden];
    }

    return popedVC;
}

-(void)pushViewController:(UIViewController *)viewController animated:(BOOL)animated {

    [super pushViewController:viewController animated:animated];
    [self setNavBarVisible];
}

-(void)setNavBarHidden {

    [self.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];
    [self.navigationBar setShadowImage:[UIImage new]];
    [self.navigationBar setTranslucent:YES];
    [self.navigationBar setBackgroundColor:[UIColor clearColor]];

}

-(void)setNavBarVisible {

    [self.navigationBar setBackgroundColor:[UIColor grayColor]];
    [self.navigationBar setBarTintColor:[UIColor grayColor]];
    [self.navigationBar setTintColor:[UIColor whiteColor]];
    [self.navigationBar setTranslucent:NO];
    [self.navigationBar setTitleTextAttributes:@{NSForegroundColorAttributeName :[UIColor whiteColor]}];
    [self.navigationBar setTitleTextAttributes:[NSDictionary dictionaryWithObjectsAndKeys: [UIColor whiteColor], NSForegroundColorAttributeName, [UIFont fontWithName:@"Roboto-Reqular" size:18], NSFontAttributeName,nil]];
    [self.navigationBar.topItem setBackBarButtonItem:[[UIBarButtonItem alloc] initWithTitle:@"" style:UIBarButtonItemStylePlain target:nil action:nil]];

}

@end

或者使用方法调配：

#import <objc/runtime.h>
#import "UINavigationController+FadeOutNavigationBar.h"

@implementation UINavigationController (FadeOutNavigationBar)

+(void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class class = [self class];

        //Swizzling view will appear
        SEL originalSelectorVWA = @selector(viewWillAppear:);
        SEL swizzledSelectorVWA = @selector(swizzled_viewWillAppear:);

        Method originalMethodVWA = class_getInstanceMethod(class, originalSelectorVWA);
        Method swizzledMethodVWA = class_getInstanceMethod(class, swizzledSelectorVWA);

        BOOL didAddMethodVWA =
        class_addMethod(class,
                        originalSelectorVWA,
                        method_getImplementation(swizzledMethodVWA),
                        method_getTypeEncoding(swizzledMethodVWA));

        if (didAddMethodVWA) {
            class_replaceMethod(class,
                                swizzledSelectorVWA,
                                method_getImplementation(originalMethodVWA),
                                method_getTypeEncoding(originalMethodVWA));
        } else {
            method_exchangeImplementations(originalMethodVWA, swizzledMethodVWA);
        }

        //Swizzling popViewControllerAnimated
        SEL originalSelectorPVCA = @selector(popViewControllerAnimated:);
        SEL swizzledSelectorPVCA = @selector(swizzled_popViewControllerAnimated:);

        Method originalMethodPVCA = class_getInstanceMethod(class, originalSelectorPVCA);
        Method swizzledMethodPVCA = class_getInstanceMethod(class, swizzledSelectorPVCA);

        BOOL didAddMethodPVCA =
        class_addMethod(class,
                        originalSelectorPVCA,
                        method_getImplementation(swizzledMethodPVCA),
                        method_getTypeEncoding(swizzledMethodPVCA));

        if (didAddMethodPVCA) {
            class_replaceMethod(class,
                                swizzledSelectorVWA,
                                method_getImplementation(originalMethodPVCA),
                                method_getTypeEncoding(originalMethodPVCA));
        } else {
            method_exchangeImplementations(originalMethodPVCA, swizzledMethodPVCA);
        }


        //Swizzling pushViewController
        SEL originalSelectorPVC = @selector(pushViewController:animated:);
        SEL swizzledSelectorPVC = @selector(swizzled_pushViewController:animated:);

        Method originalMethodPVC = class_getInstanceMethod(class, originalSelectorPVC);
        Method swizzledMethodPVC = class_getInstanceMethod(class, swizzledSelectorPVC);

        BOOL didAddMethodPVC =
        class_addMethod(class,
                        originalSelectorPVC,
                        method_getImplementation(swizzledMethodPVC),
                        method_getTypeEncoding(swizzledMethodPVC));

        if (didAddMethodPVC) {
            class_replaceMethod(class,
                                swizzledSelectorPVC,
                                method_getImplementation(originalMethodPVC),
                                method_getTypeEncoding(originalMethodPVC));
        } else {
            method_exchangeImplementations(originalMethodPVC, swizzledMethodPVC);
        }


    });
}

#pragma mark - Method Swizzling

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

    NSLog(@"current: %@",[self.topViewController class]);

    if ([NSStringFromClass([self.topViewController class]) isEqualToString:@"LoginVC"]) {
        [self setNavBarHidden];
    }

}

-(void)setNavBarHidden {

    [self.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];
    [self.navigationBar setShadowImage:[UIImage new]];
    [self.navigationBar setTranslucent:YES];
    [self.navigationBar setBackgroundColor:[UIColor clearColor]];

}

-(void)setNavBarVisible {

    [self.navigationBar setBackgroundColor:[UIColor grayColor]];
    [self.navigationBar setBarTintColor:[UIColor grayColor]];
    [self.navigationBar setTintColor:[UIColor whiteColor]];
    [self.navigationBar setTranslucent:NO];
    [self.navigationBar setTitleTextAttributes:@{NSForegroundColorAttributeName :[UIColor whiteColor]}];
    [self.navigationBar setTitleTextAttributes:[NSDictionary dictionaryWithObjectsAndKeys: [UIColor whiteColor], NSForegroundColorAttributeName, [UIFont fontWithName:@"Roboto-Reqular" size:18], NSFontAttributeName,nil]];
    [self.navigationBar.topItem setBackBarButtonItem:[[UIBarButtonItem alloc] initWithTitle:@"" style:UIBarButtonItemStylePlain target:nil action:nil]];

}

-(UIViewController*)swizzled_popViewControllerAnimated:(BOOL)animated {

    UIViewController *popedVC = [self swizzled_popViewControllerAnimated:animated];

    if ([NSStringFromClass([popedVC class]) isEqualToString:@"SignUpVC"] && [NSStringFromClass([[self topViewController] class]) isEqualToString:@"LoginVC"]) {
        [self setNavBarHidden];
    }

    return popedVC;
}

-(void)swizzled_pushViewController:(UIViewController *)viewController animated:(BOOL)animated {

    [self swizzled_pushViewController:viewController animated:animated];
    [self setNavBarVisible];
}
@end