iOS 设置导航栏完全透明

- (void)viewWillAppear:(BOOL)animated {

    [super viewWillAppear:animated];

    UIImage *image = [[UIImage alloc] init];

    //设置导航栏背景图片为一个空的image，这样就透明了

    [self.navigationController.navigationBar setBackgroundImage:image forBarMetrics:UIBarMetricsDefault];

    //去掉透明后导航栏下边的黑边

    [self.navigationController.navigationBar setShadowImage:image];

    self.navigationController.navigationBar.barStyle = UIBarStyleBlack;

    self.navigationController.navigationBar.translucent = YES;

}

- (void)viewWillDisappear:(BOOL)animated {

    [super viewWillDisappear:animated];

    [self.navigationController.navigationBar setBackgroundImage:nil forBarMetrics:UIBarMetricsDefault];

    [self.navigationController.navigationBar setShadowImage:nil];

    self.navigationController.navigationBar.barStyle = UIBarStyleDefault;

    self.navigationController.navigationBar.translucent = NO;

}