记一次连续pushViewController导致Can't add self as subview崩溃问题

线上崩溃反馈

96671211-F3FB-4532-BB8C-831DED659A0D.png

猜想崩溃原因

某一时刻、某一场景突然连续push多个界面动画相关导致（比如有说多个通知、多个回调一起执行连续push）

问题重现简化代码，

- (void)clickButton {
    
    ViewController *vc1 = ViewController.new;
    vc1.title = @"vc1";

    ViewController *vc2 = ViewController.new;
    vc2.title = @"vc2";
    
    ViewController *vc3 = ViewController.new;
    vc3.title = @"vc3";

    [self.navigationController pushViewController:vc1 animated:NO];
    [self.navigationController pushViewController:vc2 animated:YES];
    [self.navigationController pushViewController:vc3 animated:YES];

}

代码执行完在vc3点击返回vc2时候，发现vc2界面的view没有显示出来，继续点击vc2的返回按钮时候，就崩溃闪退了

解决问题

#import "ZYXNavigationController.h"

@interface ZYXNavigationController ()
@property (assign, nonatomic) BOOL isSwitching;
@property (nonatomic, strong) NSMutableArray *pushVCArr;/**< */
@end

@implementation ZYXNavigationController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.pushVCArr = [NSMutableArray array];
    self.delegate = self;
}
// 重载 push 方法
- (void)pushViewController:(UIViewController *)viewController animated:(BOOL)animated {
    
    if (animated) {
        if (self.isSwitching) {
            [self.pushVCArr addObject:viewController];// 1. 如果是动画，并且正在切换，保存viewController
            return;
        }
        self.isSwitching = YES; // 2. 否则修改状态
    }
    [super pushViewController:viewController animated:animated];
}

#pragma mark - UINavigationControllerDelegate

- (void)navigationController:(UINavigationController *)navigationController didShowViewController:(UIViewController *)viewController animated:(BOOL)animated {
    self.isSwitching = NO; // 3. 还原状态
    if (self.pushVCArr.count>0) {
        // 取出保存的vc，执行push
        UIViewController *vc = self.pushVCArr[0];
        [self pushViewController:viewController animated:YES];
        [self.pushVCArr removeObject:vc];
    }
}

@end