视觉还原

- (void) viewDidAppear:(BOOL)animated{
    UIView *view=(UIView *)[[AppDelegate appDelegate].window viewWithTag:800];
    [view removeFromSuperview];
    UIImageView *bgImage = [[UIImageView alloc]initWithFrame:CGRectMake(0, 0,320,480)];
    bgImage.tag = 800;
    [bgImage setImage:[UIImage imageNamed:@"testSubject.png"]];
    [bgImage setAlpha:0.4];
    [[AppDelegate appDelegate].window addSubview:bgImage];
}