如何安全删除观察者(Swift)

我添加了一个观察者

override func viewDidLoad()
{
    super.viewDidLoad()

    NSNotificationCenter.defaultCenter().addObserver(self, selector:"selector name", name: "observer name", object:nil)
    ...
}

在deinit中删除观察者时，

When removing observer in deinit,

deinit
{
    NSNotificationCenter.defaultCenter().removeObserver(self, forKeyPath: <some string>)
}

该应用有时会崩溃:

由于未捕获的异常"NSRangeException"而终止应用程序，原因:'无法删除观察者类"用于来自的关键路径一些字符串"NSNotificationCenter，因为它没有注册为观察者.

Terminating app due to uncaught exception 'NSRangeException', reason: 'Cannot remove an observer "class" for the key path "some string" from NSNotificationCenter because it is not registered as an observer.

所以我试图添加do/catch

So I am trying to add do/catch

deinit
{
    do{
        try NSNotificationCenter.defaultCenter().removeObserver(self, forKeyPath: <some string>)
    }catch{}
}

但是我得到警告:

catch块无法访问，因为do块中没有抛出任何错误

catch block is unreachable because no errors are thrown in do block

应用程序崩溃

当我添加尝试时

deinit
{
    do{
        try NSNotificationCenter.defaultCenter().removeObserver(self, forKeyPath: <some string>)
    }catch{}
}

我收到此警告:

在尝试表达内不会发生对throw函数的调用

no calls to throwing functions occur within try expresion

应用程序崩溃

那应该怎么做?