我有一个像这样的视图控制器:
class PublicationListViewController: UIViewController {
var publicationQuery: (() -> [Publication])!
func initWith(title: String, publicationQuery: () -> [Publication]) {
self.title = title
self.publicationQuery = publicationQuery
}
}
为什么我得到“将非转义参数'publicationQuery'分配给@escaping闭包”错误?
逃离闭包
因为通过将publicationQuery
存储到属性中,您允许它从初始化器“逃逸”(即使在initiliazer完成执行后它仍然存在,因此是保留周期的潜在原因)。为了能够做到这一点,你必须使用@escaping
注释明确地将其标记为转义:
class PublicationListViewController: UIViewController {
var publicationQuery: (() -> [String])!
// notice that now publicationQuery uses @escaping annotation
func initWith(title: String, publicationQuery: @escaping () -> [String]) {
self.title = title
self.publicationQuery = publicationQuery
}
}
阅读有关Closures documentation的Escaping Closures部分中的转义的更多信息。
防止保留周期
使用转义闭包时,必须注意不要创建保留周期。最简单的方法是在创建转义闭包时使用capture list,并在该捕获列表中明确捕获self
作为weak
参考:
// use [weak self] capture list to make sure that you don't create another strong reference to self
pubController.initWith(title: "Title") { [weak self] () -> [String] in
// use guard to safely unwrap the self
guard let `self` = self else { return }
// here self will be non-optional value that you can directly use
}