我们在开发过程中总会遇到如下场景：

1.tableviewcell(view)中的控件点击需要跳转到各种页面

2.在使用app或者开打app，需要处理远程通知的跳转

跳转总是需要CurrentViewController

在app中做跳转，我们总是需要获得一个可以ViewController来做转场动画，通常的场景就是正在展示的ViewController做push或者present，特别是在Self-Manager这种思想下,因为控件的self-manager之后需要handle事件，比如跳转

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@implementation FDAvatarView (FDAvatarViewSelfManager)
// 为后一个页面的创建增加了个 UID 参数
- (void)selfManagedConfigureWithAvatarURL:(NSURL *)URL VIPInfo:(id)info UID:(NSString *)UID {
    [self configureWithAvatarURL:URL VIPInfo:info tapped:^{
        // 假设 App 结构是 Root -> TabBar -> Navigation -> ViewController
        UITabBarController *tabBarControler = (id)[UIApplication.sharedApplication.delegate.window.rootViewController;
        UINavigationController *navigationController = tabBarControler.selectedViewController;
        // 创建用户信息 View Controller
        FDUserProfileViewController *profileViewController = [FDUserProfileViewController viewControllerWithUID:UID];
        [navigationController pushViewController:profileViewController animated:YES];
    }];
}
@end

然而控件可能会出现在各种各样的ViewController中，如何获得当前的ViewController

获得CurrentViewController

demo地址：https://github.com/Sdoy/CurrentViewController

写一个继承自UIViewController的子类，就叫BaseViewController

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@interface BaseViewController : UIViewController
@end

然后在BaseViewController中将self绑定到Application中的currentViewController属性

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@implementation BaseViewController
-(void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    [UIApplication sharedApplication].currentViewController=self;
}
@end

恩，如何绑定？
为UIApplication写一个Category

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@interface UIApplication (CurrentViewController)
@property (nonatomic, weak) UIViewController *currentViewController;
@end

.m文件
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#import "UIApplication+CurrentViewController.h"
#import <objc/runtime.h>
@implementation UIApplication (CurrentViewController)
-(void)setCurrentViewController:(UIViewController *)currentViewController
{
    objc_setAssociatedObject(self, @selector(currentViewController), currentViewController, OBJC_ASSOCIATION_ASSIGN);
}
-(UIViewController *)currentViewController
{
    return objc_getAssociatedObject(self, _cmd);
}
@end

至此，只要你的ViewController都是继承自BaseViewController，你就可以在任何地方都能拿到CurrentViewController了，调用起来是这样的

比如收到了远程通知：

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- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo {
    //You can esay find out which view controller is on the screen here.
    UIViewController *currentVC=[UIApplication sharedApplication].currentViewController;
    NSLog(@"%@",currentVC);
}

或者在子控件做跳转：

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-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
//if you want to go another view controller when you touch this view
//you don't need create a delegate to let the display or some view controller to perform SEL
    NSLog(@"%@",[UIApplication sharedApplication].currentViewController);
    AnotherViewController *another=[[AnotherViewController alloc]init];
    [[UIApplication sharedApplication].currentViewController.navigationController pushViewController:another animated:YES];
}

而且还写了3个宏定义,用起来更方便

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#define CurrentVC [UIApplication sharedApplication].currentViewController
#define PushVC(ViewController) [[UIApplication sharedApplication].currentViewController.navigationController pushViewController:ViewController animated:YES]
#define PresentVC(ViewController)\
UINavigationController *nv=[[UINavigationController alloc]initWithRootViewController:ViewController];\
[[UIApplication sharedApplication].currentViewController presentViewController:nv animated:YES completion:nil]

为什么不直接hook，UIViewController的viewWillAppear:方法？

因为很多苹果的私有组件都是继承自UIViewController的，他们也许是没有nav的.

编后：

首先感谢sunnyxx抽时间看了文章以及分享的如何获取current的代码

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@implementation UIViewController (FDTopViewController)
+ (UIViewController*)topViewControllerWithRootViewController:(UIViewController*)rootViewController {
    if ([rootViewController isKindOfClass:[UITabBarController class]]) {
        UITabBarController* tabBarController = (UITabBarController*)rootViewController;
        return [self topViewControllerWithRootViewController:tabBarController.selectedViewController];
    } else if ([rootViewController isKindOfClass:[UINavigationController class]]) {
        UINavigationController* navigationController = (UINavigationController*)rootViewController;
        return [self topViewControllerWithRootViewController:navigationController.visibleViewController];
    } else if (rootViewController.presentedViewController) {
        UIViewController* presentedViewController = rootViewController.presentedViewController;
        return [self topViewControllerWithRootViewController:presentedViewController];
    } else {
        return rootViewController;
    }
}
@end

的确，这样的方法更利于老项目的修改，而且从使用方便的角度讲比文中提到的好太多了，虽然可能多调几次方法，和多走几次if判断，但基本不会成为app性能的瓶颈。