iOS设置导航栏透明

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    [self.navigationController.navigationBar setBackgroundImage:[UIImage new]
                                 forBarMetrics:UIBarMetricsDefault];
    self.navigationController.navigationBar.shadowImage = [UIImage new];
    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.translucent = NO;
}