统一设置返回按钮

• 在 UINavigationController 中的 - (void)pushViewController: animated:方法中统一设置返回按钮
• 根控制器不需要返回按钮, 所以要先做判断是否为根控制器
• 统一设置的返回按钮一定要在调用父类的- (void)pushViewController: animated:方法之前

- (void)pushViewController:(UIViewController *)viewController animated:(BOOL)animated
{
    if (self.childViewControllers.count > 0) { // 非根控制器
        // 非根控制器才需要设置返回按钮
        // 设置返回按钮
        UIButton *backButton = [UIButton buttonWithType:UIButtonTypeCustom];
        [backButton setTitle:@"返回" forState:UIControlStateNormal];
        [backButton setImage:[UIImage imageNamed:@"navigationButtonReturn"] forState:UIControlStateNormal];
        [backButton setImage:[UIImage imageNamed:@"navigationButtonReturnClick"] forState:UIControlStateHighlighted];
        [backButton setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
        [backButton setTitleColor:[UIColor redColor] forState:UIControlStateHighlighted];
        [backButton addTarget:self action:@selector(back) forControlEvents:UIControlEventTouchUpInside];
        [backButton sizeToFit];

        // 注意:一定要在按钮内容有尺寸的时候,设置才有效果
        backButton.contentEdgeInsets = UIEdgeInsetsMake(0, -25, 0, 0);

        viewController.navigationItem.leftBarButtonItem = [[UIBarButtonItem alloc] initWithCustomView:backButton];

    }

    // 这个方法才是真正执行跳转
    [super pushViewController:viewController animated:animated];
}