防止navigation多次push一个页面

场景：快速多次点击cell跳转到另一个页面，另一个页面被push多次。

原因：push后的页面有耗时操作或者刚好push到另一个页面时，另一个页面正好在reloadData卡住主线程。造成点击cell时卡住了。

解决方法：在基类导航控制器中重写导航控制器的push方法。

#import "ZDBaseNavigationController.h"

@interface ZDBaseNavigationController ()<UINavigationControllerDelegate>
@property (nonatomic, getter=isPushing) BOOL pushing;///< 是否正在push，防止多次push同一个VC
@end

@implementation ZDBaseNavigationController

- (void)viewDidLoad {
    [super viewDidLoad];

    self.delegate = self;
}

#pragma mark - Push
- (void)pushViewController:(UIViewController *)viewController animated:(BOOL)animated {
    if (self.isPushing) {
        NSLog(@"拦截多次push同一个VC");
        return;
    } else {
        self.pushing = YES;
    }
    
    [super pushViewController:viewController animated:animated];
}

- (void)navigationController:(UINavigationController *)navigationController
       didShowViewController:(UIViewController *)viewController
                    animated:(BOOL)animated
{
    self.pushing = NO;
}