iOS 跳转显示白底, 添加渐变动画

                CATransition *transition = [CATransition animation];

                transition.duration = 0.25;

                transition.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];

                transition.type = kCATransitionFade;

                transition.subtype = kCATransitionFromRight;

                [[UIApplication sharedApplication].keyWindow.layer addAnimation:transition forKey:nil];

                [UIApplication sharedApplication].keyWindow.rootViewController = xxxx;