我正在尝试理解我正在处理的项目中的一些代码。我有一个字符串数组属性:
var names: [String]!
func findName(name: String?) -> [Name]? {
if name != nil {
return nameManager.namesForSearchString(name)?.filter({self.names.contains($0.name)})
} else {
return nameManager.allNames.filter({self.names.contains($0.name)}) //<-what get's returned here?
}
}
我不明白的是如果名称为 nil，当.contains被调用时会发生什么，以及that，什么当 .filter 被调用时会发生什么？这是在Favorites类中实现的，如果点击按钮，我需要调用这个函数来返回所有收藏夹，那么我将传递给这个函数什么来确保 Names: [Name] 的所有内容被退回？
在较低的层面上，我想了解 .contains 和 .filter 是如何工作的，以及如果将 nil 传递给它们会返回什么。
来自不同提交的相同方法的另一个版本(我也没有写)是这样的:
func findFavorites(name: String?) -> [Station]? {
if name != nil {
return nameManager.namesForSearchString(name)!.filter({contains(self.names, $0.objectId)})
} else {
return nameManager.allNames.filter({contains(self.names, $0.objectId)})
}
}
最佳答案
我不想发布非答案，但我确实希望其格式正确，所以我想评论是行不通的。这可能会帮助您了解发生了什么，以及过滤器/包含会发生什么。如果您还有其他问题，请告诉我，我会回答问题。如果我完全偏离基地，也请告诉我!
// I don't know why this is implicitely unwrapped, as a nil in this Array crashes Playground execution
var localNames: [String!] = ["Troy", "Bob", "Donald"]
// I'm just modelling what I know about NameManager
struct NameManager {
var allNames = [Name(name: "Bob"), Name(name: "Liz"), Name(name: "Anastasia")]
}
// I also assume the `name` in Name is a non-optional.
struct Name {
var name: String = "some name"
}
var nameManager = NameManager()
func findName(name: String?) -> [Name]? {
// Case where `name` is non-nil is excluded for demonstration purposes
// I have expanded all the closure short-hands so we always see what we're doing.
let allNames = nameManager.allNames
// namesMatchingName is of type [Name], that we get by applying a filter.
// `filter` works on a predicate basis: it goes through each element, one at a time,
// and checks if it meets the "predicate", that is, a boolean
// condition that returns true or false. If it DOES meet the criteria, it will be included in
let namesMatchingName = allNames.filter { (currentName) -> Bool in
// Now we're inside the filter-predicate. What we do here is check if the `currentName`
// is in `localNames`.
let namesHasCurrentName = localNames.contains(currentName.name)
// If the name IS in `localNames` we return true to the filter,
// which means it will be included in the final array, `namesMatchingName`.
return namesHasCurrentName
}
// So now we have all the names that appear in both `nameManager.allNames` and `localNames`
return namesMatchingName
}
findName(nil) // returns [{name: "Bob"}]
关于ios - Swift Array 将 nil 的 var 传递给 .contains 和 .filter 时会发生什么，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/36161997/