找window

//找window的三种方法

UIWindow *window1 = [UIApplication sharedApplication].keyWindow;

UIWindow *window2 = [UIApplication sharedApplication]windows[0];

UIWindow *window3 = [UIApplication sharedApplication].delegate.window;

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- (void)viewDidLoad {

//self本类(NowViewController)的对象

//super父类(UIViewController)的对象

//先加载父类视图,确保子类视图顺利加载

[super viewDidLoad];

//视图控制器在创建时会自动生成一个view,作为视图控制器的一个自带属性

//设置背景颜色

self.view.backgroundColor= [UIColor blueColor];

//在viewDidLoad方法中写代码

UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(100, 100, 150, 100)];

label.text = @"viewController";

[self.view addSubview:label];

[self findWindow];

}

//系统的触摸方法,当手指触摸到屏幕时调用

- (void)touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event {

//1.导入头文件

//2.创建视图控制器对象

NowViewController *vc = [[NowViewController alloc] init];

//3.找window,不能重新创建window,因为一个只能有一个window

UIWindow *window = self.view.window;

//4.设置为window的根视图控制器

window.rootViewController= vc;

//上一句代码把window的根视图控制器换掉了,所以现在self.view已经不在window上了,所以用self.view.window找不到window

//[self findWindow];

}

//找window

- (void)findWindow {

//方法一(不确定):

UIWindow *window1 =self.view.window;

//方法二(常用):

UIWindow *window2 = [UIApplication sharedApplication].keyWindow;

// UIWindow  *window2 = [[UIApplication sharedApplication] keyWindow];

//方法三:

UIWindow *window3 = [UIApplication sharedApplication].windows[0];

//方法四(最安全):

//找到应用程序

UIApplication *app = [UIApplication sharedApplication];

//UIWindow *window4 = [UIApplication sharedApplication];

//找到应用程序的入口类

AppDelegate *delegate = app.delegate;

//找到入口类中的属性window

UIWindow *window4 = delegate.window;

NSLog(@"window1 = %@",window1);

NSLog(@"window2 = %@",window2);

NSLog(@"window3 = %@",window3);

NSLog(@"window4 = %@",window4);

}