Question

我有一个[UIImageView？]数组，想迭代所有非零值。以下是我尝试过的事情：

    // Kind of work:
for imageView in imageViews where imageView != nil { // works, but still have to use imageView! rather than imageView
for tmp in imageViews { guard let imageView = tmp else { continue } // works but feels wrong, looks weird/confusing, and neems unnecessarily longwinded

    // Don't work: (in no particular order)
for x in imageViews, let imageView = x {
for let imageView in imageViews {
for (imageView in imageViews) as? UIImageView {
for imageView in imageViews as? UIImageView {
for imageView? in imageViews {
for imageView in imageViews ?? false {
for imageView in? imageViews {
for x in imageViews where let imageView = x {

Answer 1

for case let .Some(x) in imageViews {
   ...
}

甚至没有循环：

let result = imageViews.flatMap { x in ... }

你甚至可以在flatMap结果上使用普通循环：

for imageView in imageViews.flatMap({$0}) {

}

Answer 2

您正在寻找flatMap，它可以消除nils并解开剩余的Optionals。简单的测试示例：

let arr : [UIImageView?] = [nil, UIImageView(), nil, UIImageView()]
let arr2 = arr.flatMap{$0} // eliminates the nils, unwraps the optionals
for iv in arr2 {
    ...
}

在此基础上，我实际写的是什么：

let arr : [UIImageView?] = [nil, UIImageView(), nil, UIImageView()]
arr.flatMap{$0}.forEach {iv in
    print(iv) // or whatever
}

你会发现forEach往往比for...in更受欢迎，而这种链式情况就是一个很好的例子。

在for语句中展开选项

2 个答案: