实施 canClose(withDelegate:shouldClose:contextInfo:) 的最佳实践答案

【问题标题】：Best practice to implement canClose(withDelegate:shouldClose:contextInfo:)实施 canClose(withDelegate:shouldClose:contextInfo:) 的最佳实践
【发布时间】：2018-03-18 00:24:46
【问题描述】：

我第一次尝试使用基于 NSDocument 的应用程序。（Xcode 9.2、Swift 4、macOS 10.12 Sierra 和 Cocoa/AppKit）

我想知道在没有自动保存的情况下实现关闭文档的正确方法。你能告诉我关闭 NSDocument 的最佳做法吗？

当用户试图关闭文档时，会调用下面的 NSDocument 方法。

canClose(withDelegate:shouldClose:contextInfo:)

我调试了参数，发现followimng：

delegate = MyApp.Document
shouldCloseSelector = _something:didSomething:soContinue:
contextInfo = libsystem_blocks.dylib `_NSConcreteMallocBlock

显然这样的选择器不可用，所以我认为可以在这里更改如下：

override func canClose(withDelegate delegate: Any,
                       shouldClose shouldCloseSelector: Selector?,
                       contextInfo: UnsafeMutableRawPointer?) {
    let delegate : Any = self
    let shouldCloseSelector : Selector = #selector(Document.document(_:shouldClose:contextInfo:))
    super.canClose(withDelegate: delegate, shouldClose: shouldCloseSelector, contextInfo: contextInfo)
}

@objc func document(_ document : NSDocument, shouldClose flag : Bool, 
                    contextInfo: UnsafeMutableRawPointer?) {
    if document === self, flag {
        self.cleanup() // my cleanup method
        self.close() // NSDocument.close()
    }
}

deinit {
    Swift.print(#function, #line)
}

这似乎可行，但我想这不是正确的方法，因为忽略了原始参数（Selector/contextInfo）。

【问题讨论】：

标签： swift macos

【解决方案1】：

更新

我找到了解决方案。我希望这会对某人有所帮助。

private var closingBlock : ((Bool) -> Void)? = nil

override func canClose(withDelegate delegate: Any,
                       shouldClose shouldCloseSelector: Selector?,
                       contextInfo: UnsafeMutableRawPointer?) {
    let obj : AnyObject = delegate as AnyObject
    let Class : AnyClass = object_getClass(delegate)!
    let method = class_getMethodImplementation(Class, shouldCloseSelector!)
    typealias signature =
        @convention(c) (AnyObject, Selector, AnyObject, Bool, UnsafeMutableRawPointer?) -> Void
    let function = unsafeBitCast(method, to: signature.self)

    self.closingBlock = {[unowned obj, shouldCloseSelector, contextInfo] (flag) -> Void in
        function(obj, shouldCloseSelector!, self, flag, contextInfo)
    }

    let delegate : Any = self
    let shouldCloseSelector : Selector = #selector(Document.document(_:shouldClose:contextInfo:))
    super.canClose(withDelegate: delegate, shouldClose: shouldCloseSelector, contextInfo: contextInfo)
}

@objc func document(_ document : NSDocument, shouldClose flag : Bool,
                    contextInfo: UnsafeMutableRawPointer?) {
    if flag {
        self.cleanup() // my cleanup method
    }

    self.closingBlock?(flag)
    self.closingBlock = nil
}

override func close() {
    Swift.print(#function, #line, #file)
    super.close()
}

deinit {
    Swift.print(#function, #line, #file)
}

参考资料

https://developer.apple.com/library/content/releasenotes/AppKit/RN-AppKitOlderNotes/

对遵循委托的方法的重写的建议：didSomethingSelector:contextInfo: Pattern

https://github.com/DouglasHeriot/canCloseDocumentWithDelegate/blob/master/canCloseDocumentWithDelegate/Document.swift

展示了如何使用 Swift 实现 NSDocument 方法 -canCloseDocumentWithDelegate:shouldCloseSelector:contextInfo:。必须使用 Objective-C 来执行 NSInvocation。

【讨论】：