Swift上的块（animateWithDuration：动画：完成:) [英] Blocks on Swift (animateWithDuration:animations:completion:)

问题描述

我无法让这些块在Swift上运行。这是一个有效的例子（没有完成块）：

I'm having trouble making the blocks work on Swift. Here's an example that worked (without completion block):

UIView.animateWithDuration(0.07) {
    self.someButton.alpha = 1
}

或者没有尾随闭包：

UIView.animateWithDuration(0.2, animations: {
    self.someButton.alpha = 1
})

但是一旦我尝试添加完成块，它就不起作用：

but once I try to add the completion block it just won't work:

UIView.animateWithDuration(0.2, animations: {
    self.blurBg.alpha = 1
}, completion: {
    self.blurBg.hidden = true
})

自动完成功能让我完成： （（Bool） - > Void）？但不确定如何使它工作。也尝试使用尾随闭包，但得到了同样的错误：

The autocomplete gives me completion: ((Bool) -> Void)? but not sure how to make it work. Also tried with trailing closure but got the same error:

！无法找到接受所提供参数的'animateWithDuration的重载

// This is how I do regular animation blocks
UIView.animate(withDuration: 0.2) {
    <#code#>
}

// Or with a completion block
UIView.animate(withDuration: 0.2, animations: {
    <#code#>
}, completion: { _ in
    <#code#>
})

我没有使用尾随闭包来完成块，因为我认为它缺乏清晰度，但如果你喜欢它，那么你可以看到 Trevor在下面的回答。

I don't use the trailing closure for the completion block because I think it lacks clarity, but if you like it then you can see Trevor's answer below.

推荐答案

animateWithDuration中的完成参数采用一个带有一个布尔参数的块。在swift中，就像在Obj C块中一样，你必须指定一个闭包所需的参数：

the completion parameter in animateWithDuration takes a block which takes one boolean parameter. In swift, like in Obj C blocks, you must specify the parameters that a closure takes:

UIView.animateWithDuration(0.2, animations: {
    self.blurBg.alpha = 1
}, completion: {
    (value: Bool) in
    self.blurBg.hidden = true
})

这里的重要部分是（值：Bool）。这告诉编译器这个闭包采用Bool标记为'value'并返回void。

The important part here is the (value: Bool) in. That tells the compiler that this closure takes a Bool labeled 'value' and returns void.

作为参考，如果你想写一个返回bool的闭包，语法会是

For reference, if you wanted to write a closure that returned a bool the syntax would be

{(value: Bool) -> bool in
    //your stuff
}

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