在导航控制器的边框绘制阴影

    UIColor *color = [UIColor redColor];

    CGSize offset = CGSizeMake(0, 3);

    float radius = 2;

    float opacity = 1;

    self.navigationController.view.layer.shadowColor = color.CGColor;

    self.navigationController.view.layer.shadowOffset = offset;

    self.navigationController.view.layer.shadowRadius = radius;

    self.navigationController.view.layer.shadowOpacity = opacity;