ios - Swift 中的 KVO/异常处理

Question

Please note that this question was written in july 2014, before swift 1.0 when I mostly ignored anything about swift and tried to "translate" code from objC to swift. This is not a good solution and I now know better. KVO is something we love in ObjC, but I strongly recommend not to use it in swift and explore some alternative in swift. http://blog.scottlogic.com/2015/02/11/swift-kvo-alternatives.html. Remember: if something is hard to do, then maybe it is not meant to be done.

作为一名 obj-C 开发人员，我已经习惯 KVO 好一年了，其中一个反复出现的问题是调用 removeObserver:forKeyPath: 的潜在不安全性我通常用 @try...@catch 子句包围它...现在有了 swift，我还没有找到 try ... catch thingy :)关于如何解决该问题的任何线索？

干杯

下面是我的意思的例子

override func viewDidLoad()
{
    super.viewDidLoad();

    self.summaryTextView.text = self.show?.overview;
    self.title = self.show?.title;
    if(self.show?.imageData)
    {
        self.posterImageView.image = UIImage(data: self.show?.imageData);
    }
    else
    {
        self.posterImageView.image = UIImage(named:"wait");
        show?.addObserver(self, forKeyPath: "imageData", options: NSKeyValueObservingOptions.New, context: nil);
    }

}


override func viewDidDisappear(animated: Bool)
{
     // Will crash if self was not a observer in the first place
     self.show?.removeObserver(self, forKeyPath:"imageData");
}

override func observeValueForKeyPath(keyPath: String!, ofObject object: AnyObject!, change: NSDictionary!, context: CMutableVoidPointer)
{
     self.posterImageView.image = UIImage(data: self.show?.imageData);

}

Answer 1

正如另一个答案所说，Swift 中还没有 try-catch。老实说，我不鼓励在您提到的场景中使用 try/catch。这可以通过跟踪对象的状态轻松解决，这在面向对象编程中总是一件好事。