方法1：_staWindow是UIWindow类型，必须声明为全局变量
··· CGRect rect = [UIApplication sharedApplication].statusBarFrame;
_staWindow = [[UIWindow alloc]initWithFrame:rect];
_staWindow.backgroundColor = [UIColor redColor];
//windowLevel有三个等级，normal会形成状态栏的底色，其余两个等级（StatusBar，Alert）会遮盖住状态栏
_staWindow.windowLevel = UIWindowLevelNormal;
//必须设置不可隐藏，否则会不显示当前遮盖视图
_staWindow.hidden = NO;···
方法2：局部变量遮盖法，效果一样
···CGRect rect = [UIApplication sharedApplication].statusBarFrame;
UIView *view = [[UIView alloc]initWithFrame:rect];
view.hidden = NO;
view.backgroundColor = [UIColor redColor];
UIWindow *win = [UIApplication sharedApplication].keyWindow;···
等级大于等于1000（status等级）即可遮盖
··· win.windowLevel = 1000;
[win addSubview:view];···
