自定义导航栏的返回按钮

UIBarButtonItem *left = [[UIBarButtonItem alloc] initWithTitle:@"返回3" style:UIBarButtonItemStyleDone target:self action:@selector(onBack:)];
    self.navigationItem.leftBarButtonItem = left;

//另外自定义的按钮后 就不能使用自带的右滑返回手势,参考
//http://blog.sina.com.cn/s/blog_6080da130101p6mu.html

-(void) onBack:(id)sender
{
//    [self dismissViewControllerAnimated:YES completion:nil]; 使用这个不行
    [self.navigationController popViewControllerAnimated:YES];
}