presentViewController 到半透明的 viewController

presentViewController 到一个半透明的viewController

    FirstViewController *fvc = [self getFirstViewController];
    SecondViewController *svc = [[SecondViewController alloc] init];
    if ([[[UIDevice currentDevice] systemVersion] floatValue]>=8.0) {
        [svc setModalPresentationStyle:UIModalPresentationOverCurrentContext];
    }else{
        [fvc setModalPresentationStyle:UIModalPresentationCurrentContext];
    }
    [fvc presentViewController:svc animated:YES completion:nil];