//uiwindow创建的四个步骤
//(1)给大小
self.window = [[UIWindow alloc]initWithFrame:[UIScreen mainScreen].bounds];
(2)给颜色
self.window.backgroundColor = [UIColor whiteColor];
(3)可视化
[self.window makeKeyAndVisible];
(4)设置根控制器
viewViewController *viewc = [[viewViewController alloc]init];
//设置一个导航控制器
UINavigationController *navi = [[UINavigationController alloc]initWithRootViewController:viewc];
self.window.rootViewController = navi;
