@interface RootViewController : UIViewController{      UIView        *view;}

 

-(void)createBackgroundView{    view = [[UIView alloc]initWithFrame:self.view.frame];    view.backgroundColor = [[UIColor blackColor] colorWithAlphaComponent:0.0];    view.opaque = NO;

UIWindow *appWindow = [[UIApplicationsharedApplication] keyWindow];

[appWindow addSubview:view]; //覆盖全屏

[self.view addSubview:view];    [UIView animateWithDuration:0.2 animations:^{        view.backgroundColor = [[UIColor blackColor] colorWithAlphaComponent:0.25];    }];}