找window的三种方法

LoginViewController * loginVC = [[LoginViewController alloc]init];
找window的三种方式

1、// UIWindow * window = [UIApplication sharedApplication].delegate.window;等同于 UIWindow * window = [[[UIApplication sharedApplication]delegate]window];

2、// UIWindow * window = [UIApplication sharedApplication].keyWindow;
3、 UIWindow * window = [[UIApplication sharedApplication].windows objectAtIndex:0];
window.rootViewController = loginVC;