swift 闭包中 gcd 中的弱自我

Question

    apiFunc(user: User.currentUser, start: 0, limit: Constants.numberOfItemInOnePage,
        success: { [weak self] (friends) -> Void in
            dispatch_async(dispatch_get_main_queue(), { [weak self] () -> Void in
                if let strongSelf = self {
                    strongSelf.friendList = friends
                    strongSelf.loading = false
                    strongSelf.tableView.reloadData()
                }
            })
        }, failure: nil)

错误

Command /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swiftc failed with exit code 1

编译上面的代码时会发生，但是如果我删除第二个[weak self]，错误就会消失

    apiFunc(user: User.currentUser, start: 0, limit: Constants.numberOfItemInOnePage,
        success: { [weak self] (friends) -> Void in
            dispatch_async(dispatch_get_main_queue(), { () -> Void in
                if let strongSelf = self {
                    strongSelf.friendList = friends
                    strongSelf.loading = false
                    strongSelf.tableView.reloadData()
                }
            })
        }, failure: nil)

我觉得因为有2个闭包，所以应该是2个[weak self]，谁知道为什么会出现编译错误

Answer 1

您不必像 Objective-C.

中的 @weakify 或 __weak self 模式一样在嵌套闭包中重复 [weak self]

[weak self] in Swift 编译器自动创建相同的模式，weak self 由外层闭包定义，内层闭包使用。

Objective-C版本对应的问题如下： iOS blocks and strong/weak references to self

swift 闭包中 gcd 中的弱自我

weak self in gcd in swift closure

swift

closures

grand-central-dispatch

weak-references