隐藏navgationbar底部的线，并且将底部设置为阴影

1、创建一个UIImageView，因为navgationbar底部的线其实就是一个imageView

@property (nonatomic, strong) UIImageView * navBarHairlineImageView;

2、找到这条线，隐藏或删除，

- (UIImageView*)findHairlineImageViewUnder:(UIView*)view {
    if([view isKindOfClass:UIImageView.class] && view.bounds.size.height<=1.0) {
        return(UIImageView*)view;
    }
    for(UIView * subview in view.subviews) {
        UIImageView * imageView = [self findHairlineImageViewUnder:subview];
        if(imageView) {
            return imageView;
        }
    }
    return nil;
}

3、在viewWillAppear中设置这些东西

-(void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    
    // 设置底部阴影
    self.navigationController.navigationBar.layer.shadowColor = [UIColor blackColor].CGColor;
    self.navigationController.navigationBar.layer.shadowOffset = CGSizeMake(2, 2);
    self.navigationController.navigationBar.layer.shadowOpacity = 0.1;
    self.navigationController.navigationBar.layer.shadowRadius = 4.0;
    
    //隐藏底部细线
    _navBarHairlineImageView= [self findHairlineImageViewUnder:self.navigationController.navigationBar];
    _navBarHairlineImageView.hidden = YES;
}

4、如果你在其他页面不需要此设置，那么你可以在viewWillDisappear中取消隐藏，或其他设置

- (void)viewWillDisappear:(BOOL)animated {
    
    [super viewWillDisappear:animated];
    _navBarHairlineImageView.hidden = NO;
}

还有一个问题就是，有可能除了底部的imageView还有其他的navgationbar的子视图，那么我们同理，可以循环着找到这些高度小于1，安全起见，我选择高度小于2的子视图都移除

@property (nonatomic, strong) UIView * navView;
@property (nonatomic, strong) UIView * navView1;

-(void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    
    self.navigationController.navigationBar.layer.shadowColor = [UIColor blackColor].CGColor;
    self.navigationController.navigationBar.layer.shadowOffset = CGSizeMake(2, 2);
    self.navigationController.navigationBar.layer.shadowOpacity = 0.1;
    self.navigationController.navigationBar.layer.shadowRadius = 4.0;

    _navBarHairlineImageView= [self findHairlineImageViewUnder:self.navigationController.navigationBar];
    _navView = [self findHairlineViewUnder:self.navigationController.navigationBar];
    [_navView removeFromSuperview];
    _navView1 = [self findHairlineViewUnder:self.navigationController.navigationBar];
    [_navView1 removeFromSuperview];
    
    _navBarHairlineImageView.hidden = YES;
    _navView.hidden = YES;
    _navView1.hidden = YES;
}

// 找到所有高度小于2的线
- (UIView*)findHairlineViewUnder:(UIView*)view {
    for(UIView * subview in view.subviews) {
        if (subview.bounds.size.height < 2.0) {
            return subview;
        }
    }
    return nil;
}

以上方法应该可以解决了，如果还有的话，就多弄几个，直到不可能出现为止。