获取rootViewController 之window

你一般怎么获取工程中window上面的RootViewController

第一种方法:

UIWindow *window = [UIApplication sharedApplication].keyWindow;

UIViewController *rootViewController = window.rootViewController;

第二种方法:

AppDelegate *appdelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;

UIViewController *rootViewController1 = appdelegate.window.rootViewController;

这两种写法,在平常的时候是没有区别的,但是这两种写法在有的时候就不一样了。

keyWindow这个属性是什么意思?

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个人理解的意思是,在windows数组中,最近时间调用makeKeyAndVisible方法的属性。

当然可以参考关于UIAlertView显示的相关内容:

http://www.jianshu.com/p/7ac398ef4532

http://stackoverflow.com/questions/5968703/how-to-find-root-uiviewcontroller

alertView的出现是因为,生成了一个新的window,加在了界面上面。这个时候获取到的keyWindow就是UIAlertControllerShimPresenterWindow。可以通过如下代码实验:

Appdelegate中的代码,设置RootViewController

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

// Override point for customization after application launch.

self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];

self.window.backgroundColor = [UIColor whiteColor];

ViewController *view = [[ViewController alloc] init];

UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:view];

self.window.rootViewController = nav;

[self.window makeKeyAndVisible];

return YES;

}

ViewController中的代码

- (void)viewDidLoad {

[super viewDidLoad];

// Do any additional setup after loading the view, typically from a nib.

UIButton *tempBtn = [UIButton buttonWithType:UIButtonTypeSystem];

tempBtn.frame = CGRectMake(100, 100, 100, 100);

tempBtn.backgroundColor = [UIColor cyanColor];

[tempBtn setTitle:@"测试1" forState:UIControlStateNormal];

[tempBtn addTarget:self action:@selector(clickBtn:) forControlEvents:UIControlEventTouchUpInside];

[self.view addSubview:tempBtn];

}

- (void)clickBtn:(UIButton *)sender{

// 创建一个测试的alertView

UIAlertView *alterView = [[UIAlertView alloc] initWithTitle:@"测试" message:@"测试" delegate:nil cancelButtonTitle:@"取消" otherButtonTitles:nil, nil];

[alterView show];

UIWindow *window1 = [UIApplication sharedApplication].keyWindow;

AppDelegate *appdelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;

UIWindow *window2 = appdelegate.window;

NSLog(@"\n\nwindow1 = %@    \n\nwindow2 = %@  \n\nwindow1.rootViewController = %@ \n\nwindow2.rootViewController = %@",window1,window2,window1.rootViewController,window2.rootViewController);

}

打印结果:

window1 = <_UIAlertControllerShimPresenterWindow: 0x7fb4ab720c80; frame = (0 0; 375 667); opaque = NO; gestureRecognizers = ; layer = >

window2 = ; layer = >

window1.rootViewController =

window2.rootViewController =

结果明显不一样,其实我们一般情况下想获取的rootViewController是第二种,希望我们获取到在appdelegate中设置的appdelaget.window.rootViewController。

所以了建议获取rootViewController的时候还是采用

第二种方法:

AppDelegate *appdelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;

UIViewController *rootViewController1 = appdelegate.window.rootViewController;

其实,和alertView类似的,UIActionSheet也是这样的。

一般人说无所谓,但是如果在AlertView弹出的时候去获取RootViewController,并且对你认为获取正确的RootViewController做相关的操作,你会死的很惨。

还有就是建议:即时通过第二种方法获取到了RootViewController,在使用之前建议再判断一下获取到的类是不是就是自己想要的类型,更保险一些。

AppDelegate *appdelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;

if ([appdelegate.window.rootViewController isKindOfClass:["想要获取到的rootVC" class]] == YES) {

// 为所欲为

}

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