如何监听UIViewController展示事件？分析框架页面转场检测方法

要实现全局监听ViewController的展示、计算特定VC的展示时长，无需修改每一处present/push调用，常用且高效的方案是Method Swizzling（方法交换），下面是具体实现思路和代码：

核心思路 #

通过交换UIViewController（及UINavigationController）的关键方法，在不侵入原有业务代码的前提下，注入自定义的跟踪逻辑：

• 交换presentViewController:animated:completion:，监听模态弹出的VC
• 交换pushViewController:animated:，监听导航栈推入的VC
• 交换viewDidAppear:/viewDidDisappear:，准确获取VC的展示/消失时机，计算时长

具体代码实现 #

1. UIViewController分类：处理模态与展示时长跟踪 #

创建UIViewController+Tracking分类：

#import <UIKit/UIKit.h>
#import <objc/runtime.h>

@implementation UIViewController (Tracking)

+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        // 交换presentViewController方法
        [self swizzleOriginalSelector:@selector(presentViewController:animated:completion:)
                     withSwizzledSelector:@selector(swizzled_presentViewController:animated:completion:)];
        
        // 交换viewDidAppear方法
        [self swizzleOriginalSelector:@selector(viewDidAppear:)
                     withSwizzledSelector:@selector(swizzled_viewDidAppear:)];
        
        // 交换viewDidDisappear方法
        [self swizzleOriginalSelector:@selector(viewDidDisappear:)
                     withSwizzledSelector:@selector(swizzled_viewDidDisappear:)];
    });
}

/// 通用方法交换工具
+ (void)swizzleOriginalSelector:(SEL)originalSelector withSwizzledSelector:(SEL)swizzledSelector {
    Method originalMethod = class_getInstanceMethod(self, originalSelector);
    Method swizzledMethod = class_getInstanceMethod(self, swizzledSelector);
    
    BOOL didAddMethod = class_addMethod(self, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
    if (didAddMethod) {
        class_replaceMethod(self, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
    } else {
        method_exchangeImplementations(originalMethod, swizzledMethod);
    }
}

/// 交换后的present方法
- (void)swizzled_presentViewController:(UIViewController *)viewControllerToPresent animated:(BOOL)flag completion:(void (^)(void))completion {
    // 先执行原present逻辑
    [self swizzled_presentViewController:viewControllerToPresent animated:flag completion:^{
        if (completion) completion();
        // 注入跟踪逻辑
        [self startTrackingForVC:viewControllerToPresent];
    }];
}

/// 交换后的viewDidAppear：处理导航栈推入的VC（因为push没有completion回调）
- (void)swizzled_viewDidAppear:(BOOL)animated {
    [self swizzled_viewDidAppear:animated];
    // 导航栈推入的VC在这里触发跟踪（避免重复触发模态的情况）
    if (!self.presentingViewController) {
        [self startTrackingForVC:self];
    }
}

/// 交换后的viewDidDisappear：计算展示时长
- (void)swizzled_viewDidDisappear:(BOOL)animated {
    [self swizzled_viewDidDisappear:animated];
    // 获取记录的开始时间
    NSNumber *startTime = objc_getAssociatedObject(self, _cmd);
    if (startTime) {
        NSTimeInterval duration = CACurrentMediaTime() - startTime.doubleValue;
        // 检查是否为目标VC，执行额外操作
        if ([self.restorationIdentifier isEqualToString:@"TargetVC"]) {
            NSLog(@"目标VC展示时长：%.2f秒", duration);
            // 这里可以添加上报统计、业务逻辑等操作
        }
        // 清除关联数据
        objc_setAssociatedObject(self, _cmd, nil, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
}

/// 开始跟踪VC
- (void)startTrackingForVC:(UIViewController *)vc {
    if ([vc.restorationIdentifier isEqualToString:@"TargetVC"]) {
        // 记录展示开始时间（用关联对象存储，避免添加属性）
        objc_setAssociatedObject(vc, @selector(swizzled_viewDidDisappear:), @(CACurrentMediaTime()), OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
}

@end

2. UINavigationController分类：处理导航栈推入 #

创建UINavigationController+Tracking分类，确保push的VC也能被监听：

#import <UIKit/UIKit.h>
#import <objc/runtime.h>

@implementation UINavigationController (Tracking)

+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        [self swizzleOriginalSelector:@selector(pushViewController:animated:)
                     withSwizzledSelector:@selector(swizzled_pushViewController:animated:)];
    });
}

+ (void)swizzleOriginalSelector:(SEL)originalSelector withSwizzledSelector:(SEL)swizzledSelector {
    Method originalMethod = class_getInstanceMethod(self, originalSelector);
    Method swizzledMethod = class_getInstanceMethod(self, swizzledSelector);
    
    BOOL didAddMethod = class_addMethod(self, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
    if (didAddMethod) {
        class_replaceMethod(self, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
    } else {
        method_exchangeImplementations(originalMethod, swizzledMethod);
    }
}

- (void)swizzled_pushViewController:(UIViewController *)viewController animated:(BOOL)animated {
    [self swizzled_pushViewController:viewController animated:animated];
    // 标记即将被push的VC，避免在viewDidAppear中重复处理
    objc_setAssociatedObject(viewController, @"isPushedByNav", @YES, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

@end

注意事项 #

• Method Swizzling必须在+load方法中执行，用dispatch_once保证仅交换一次，避免重复操作。
• 视图标识符建议使用restorationIdentifier，或给VC添加自定义属性标识，确保能准确识别目标VC。
• 如果项目中存在自定义的present/push封装方法，需要针对性交换对应的自定义方法。
• 注意与第三方库的方法交换冲突，可通过检查方法实现是否被修改来规避。

关于你提到的NotificationCenter/Darwin通知 #

系统并没有默认发送ViewController展示/消失的通知，你之前的记忆可能是项目中自行埋点发送的通知，而非系统原生支持。目前全局监听最可靠的方案还是Method Swizzling。

内容的提问来源于stack exchange，提问作者Ghean Ginanjar Adiguna