ios UIwindow

// UIWindowView
//UIwindow 本身就是一个窗体，不需要添加什么父窗体？
UIWindow *window1 = [[UIWindow alloc]initWithFrame:CGRectMake(0, 0, 320, 320)];
window1.backgroundColor = [UIColor blueColor];
//默认UIwindow是隐藏的
window1.hidden = NO;

//UIwindow的级别
UIWindow *window2 = [[UIWindow alloc]initWithFrame:CGRectMake(0, 0, 320, 200)];
window2.backgroundColor = [UIColor redColor];
window2.hidden = NO;
//级别是状态栏级别，会遮盖状态栏
window2.windowLevel = UIWindowLevelStatusBar;

UIWindow *window3 = [[UIWindow alloc]initWithFrame:CGRectMake(0, 0, 320, 100)];
window3.backgroundColor = [UIColor purpleColor];
window3.hidden = NO;
//级别更高，会遮盖状态栏
window3.windowLevel = UIWindowLevelAlert;