Cocoa 脚本:返回“null"与“缺失值"对比

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问题描述

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AppleScript 似乎知道特殊值 null.

It appears that AppleScript knows the special value null.

如何从基于 Cocoa Scripting 的应用程序中为可编写脚本的属性返回这样的值?

How do I return such a value from my Cocoa Scripting based app for a scriptable property?

如果我从基于 Cocoa Scripting 的应用程序返回 nil (NULL) 或 NSNull作为缺失值.

If I return nil (NULL) or NSNull for a scriptable property getter from my Cocoa Scripting-based app, the script editor interprets that as missing value.

如果我返回 [NSAppleEventDescriptor nullDescriptor]，AppleScript 甚至会显示错误.

And if I return [NSAppleEventDescriptor nullDescriptor], AppleScript even shows an error.

推荐答案

我正在使用null"的 cMissingValue 版本，如下所示:

I'm using the cMissingValue version of "null", like so:

NSAppleEventDescriptor(typeCode: UInt32(cMissingValue))

我决定根据下面的测试使用它.

I decided to use that based on the testing below.

我使用 Swift 运行并将参数传递给 AppleScript 子例程，使用以下代码:

I'm using Swift to run and passing parameters to an AppleScript subroutine, using the code here:

将变量传递给 AppleScript

let parameters = NSAppleEventDescriptor.list()

let null         = NSAppleEventDescriptor.null()
let missingValue = NSAppleEventDescriptor(typeCode: UInt32(cMissingValue))

parameters.insert(null, at: 0)
parameters.insert(missingValue, at: 0)
return parameters

这些参数被传递给 AppleScript 子程序，我已经对每个结果进行了注释:

These parameters are passed to the AppleScript subroutine, and I've commented each results:

on nilTest(paramNull, paramMissingValue)
    display dialog paramNull buttons {"OK"} # execution error: Can’t make current application into type string. (-1700)
    display dialog paramMissingValue buttons {"OK"} #"msng"

    display dialog "" & paramNull buttons {"OK"} #"current application"
    display dialog "" & paramMissingValue buttons {"OK"} #"missing value"
end nilTest

NSAppleEventDescriptor.null() 版本似乎出于某种原因正在获取当前应用程序"值.

The NSAppleEventDescriptor.null() version seems to for some reason be getting the "current application" value.

似乎我可能想要使用 cMissingValue，如另一个答案中所示.

It seems like I may want to use the cMissingValue as shown in the other answer.

可以像这样在 AppleScript 中对变量进行 nil-check:

The variables can be nil-checked in AppleScript like so:

if yourVar is missing value then
    display dialog "is missing value" buttons {"OK"}
end if

NSAppleEventDescriptor.null()没有点击这个检查.输入 cMissingValue 即可.

NSAppleEventDescriptor.null() does not hit this check. Type cMissingValue does.

我已将其添加为 Swift 扩展:NSAppleEventDescriptor.missingValue()

I've added it as a Swift Extension: NSAppleEventDescriptor.missingValue()

extension NSAppleEventDescriptor {

    static func missingValue() -> NSAppleEventDescriptor {
        return NSAppleEventDescriptor(typeCode: UInt32(cMissingValue))
    }

}

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