方法一：通过ViewController的属性presentingViewController判断当前页面是否是被present出的，来确定采用dismiss方法
- (void)backAction
{
if (self.presentingViewController)
{
[self dismissViewControllerAnimated:YES completion:nil];
}
else
{
[self.navigationController popViewControllerAnimated:YES];
}
方法二：通过NavgationController的属性topViewController判断当前页面是否是被push出的最上层页面，来确定采用pop方法 - (void)backAction
{
if (self.navigationController.topViewController == self)
{
[self.navigationController popViewControllerAnimated:YES];
}
else
{
[self dismissViewControllerAnimated:YES completion:nil];
}
}
方法三：通过NavgationController的属性viewcontrollers数组索引，来判断当前页面是否是被push过，来确定采用dismiss方法 - (void)backAction
{
if ([self.navigationController.viewControllers.firstObject isEqual:self])
{//当前页面尚未被Push过
[self dismissViewControllerAnimated:YES completion:nil];
}
else
{
[self.navigationController popViewControllerAnimated:YES];
}
}
