- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
[self.navigationController.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];
[self.navigationController.navigationBar setShadowImage:[UIImage new]];
}

- (void)viewWillDisappear:(BOOL)animated
{
[super viewWillDisappear:animated];
[self.navigationController.navigationBarsetBackgroundImage:nil forBarMetrics:UIBarMetricsDefault];
[self.navigationController.navigationBar setShadowImage:nil];
}

给UIImage增加分类设置透明

- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
[self.navigationController.navigationBar setBackgroundImage:[UIImage imageWithColor:[UIColor clearColor] size:CGSizeMake(self.view.frame.size.width, 64)] forBarPosition:UIBarPositionAny barMetrics:UIBarMetricsDefault];
[self.navigationController.navigationBar setShadowImage:[UIImage new]];
}

- (void)viewWillDisappear:(BOOL)animated
{
[super viewWillDisappear:animated];
[self.navigationController.navigationBar setBackgroundImage:nil forBarPosition:UIBarPositionAny barMetrics:UIBarMetricsDefault];
[self.navigationController.navigationBar setShadowImage:nil];
}

+ (UIImage *)imageWithColor:(UIColor *)color size:(CGSize)size
{
if (!color || size.width <= 0 || size.height <= 0) return nil;
CGRect rect = CGRectMake(0, 0, size.width, size.height);
UIGraphicsBeginImageContextWithOptions(rect.size, NO, 0);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(context, color.CGColor);
CGContextFillRect(context, rect);
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}