自定义函数的 CompletionHandler for Dummies

Question

我在互联网上到处搜索，但无法真正处理我找到的答案。因此，如果有人可以在这里帮助我，那将不胜感激。

我写了一个看起来像这样的函数：

func setImage(imageName: String, completion: ((String) -> Void)?) {
    UIView.transitionWithView(self.myImageView, duration: 0.3, options: .CurveEaseOut, animations: {
        self.lockImageView.image = UIImage(named: "\(imageName).png")
        }, completion: { finished in
            //execute the completionBlock that was passed
    })
}

我这样称呼它：

setImage("lockCheck", completion: { finished in
    print("done")
})

现在，我该如何执行作为完成传递的任何内容？
在函数中，在转换的完成块中，我尝试了类似

for x in completion {self.x}

但这没有用。

提前致谢:)

Answer 1

例如，您可以像这样在动画块的 completionHandler 中立即执行完成处理程序：

func setImage(imageName: String, completion: ((Bool) -> Void)?) {
    UIView.transitionWithView(self.myImageView, duration: 0.3, options: .CurveEaseOut, animations: { () -> Void in
            self.lockImageView.image = UIImage(named: "\(imageName).png")
        }, completion: completion)
}

您还可以运行带有额外参数的完成处理程序，如下所示（我希望这样清楚）：

func setImage(imageName: String, completion: ((Bool, String) -> Void)?) {
    UIView.transitionWithView(self.lockImageView, duration: 0.3, options: .CurveEaseOut, animations: { () -> Void in
        self.lockImageView.image = UIImage(named: "\(imageName).png")
            }) { (finished) -> Void in

            // Do some things for example print
            print("Hi, this is the animation completion handler")

            // Notice the ? because the completion handler is an optional
            completion?(finished, "some string")

    }
}

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