一行代码巧妙实现iOS返回button:

self.navigationItem.leftBarButtonItem = [[UIBarButtonItem alloc]initWithImage:[[UIImage imageNamed:@"back"] imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal]  style:UIBarButtonItemStyleDone target:self.navigationController action:@selector(popViewControllerAnimated:)];