ios 添加伪闪屏

 　　self.window.rootViewController.view.alpha = ;
     UIImageView *splashImageView = [[UIImageView alloc]initWithImage:[UIImage imageNamed:@"Defauit_o"]];
     splashImageView.frame=CGRectMake(, , ScreenWidth, ScreenHeight);
     [self.window addSubview:splashImageView];
     [UIView animateWithDuration:1.7 animations:^{
         self.window.rootViewController.view.alpha = 1.0;
     } completion:^(BOOL finished) {
         [splashImageView removeFromSuperview];
     }];