展开可选值时意外发现 nil（AppleScript 结果）

Question

我正在尝试在 Swift 2 中制作一个程序，该程序运行并获取 AppleScript 脚本的结果。

这是我的代码：

import Foundation

func runAppleScript(script:String) -> String
{
    let errorInfo = AutoreleasingUnsafeMutablePointer<NSDictionary?>()
    let startAtLoginScript: NSAppleScript = NSAppleScript(source: script)!
    let theDiscriptor:NSAppleEventDescriptor = startAtLoginScript.executeAndReturnError(errorInfo)
    let theResult:String = theDiscriptor.stringValue! //This is whats causing the error

    return theResult
}

let scriptResult = runAppleScript("tell app \"Spotify\" to playpause")

NSLog("\(scriptResult)")

问题是程序崩溃并输出：

fatal error: unexpectedly found nil while unwrapping an Optional value

在控制台中。我也试过 if let else，但这也不起作用。我该如何解决这个问题？

这是使用 swift 语言使用 OS X 命令行模板测试的。

Answer 1

实际上错误可能来自 NSAppleScript(source: script)! 所以 正确的 解决方案是 return 一个可选字符串而不是使用强制展开完全:

func runAppleScript(script:String) -> String? {
    let errorInfo: AutoreleasingUnsafeMutablePointer<NSDictionary?> = nil
    let startAtLoginScript = NSAppleScript(source: script)
    let theDescriptor = startAtLoginScript?.executeAndReturnError(errorInfo)
    return theDescriptor?.stringValue
}

if let scriptResult = runAppleScript("tell app \"Spotify\" to playpause") {
    NSLog("\(scriptResult)")
} else {
    print("the script execution failed")
}

如果您希望在失败时使用默认值而不是 nil，则无需 return 可选：

func runAppleScript(script:String) -> String {
    let errorInfo: AutoreleasingUnsafeMutablePointer<NSDictionary?> = nil
    let startAtLoginScript = NSAppleScript(source: script)
    let theDescriptor = startAtLoginScript?.executeAndReturnError(errorInfo)
    return theDescriptor?.stringValue ?? ""  // if nil, returns the default ""
}

let scriptResult = runAppleScript("tell app \"Spotify\" to playpause")
NSLog("\(scriptResult)")

至于使用新的 Swift 2 错误处理系统，none 您在 runAppleScript 中使用的方法正在抛出错误，所以它只有在你使用自定义错误类型并自己抛出错误时才有效。示例：

enum MyAppleScriptError: ErrorType {
    case ExecutingScriptFailed
    case GettingStringValueFailed
}

func runAppleScript(script:String) throws -> String {
    let errorInfo: AutoreleasingUnsafeMutablePointer<NSDictionary?> = nil
    let startAtLoginScript = NSAppleScript(source: script)
    guard let theDescriptor = startAtLoginScript?.executeAndReturnError(errorInfo) else {
        throw MyAppleScriptError.ExecutingScriptFailed
    }
    guard let value = theDescriptor.stringValue else {
        throw MyAppleScriptError.GettingStringValueFailed
    }
    return value
}

do {
    let scriptResult = try runAppleScript("tell app \"Spotify\" to playpause")
    NSLog("\(scriptResult)")
} catch {
    print(error)
}

Swift 3

相同的想法，但一些实现细节不同。

func runAppleScript(_ script:String) -> String? {
    let errorInfo: AutoreleasingUnsafeMutablePointer<NSDictionary?>? = nil
    if let startAtLoginScript = NSAppleScript(source: script) {
        let theDescriptor = startAtLoginScript.executeAndReturnError(errorInfo)
        return theDescriptor.stringValue
    }
    return nil
}

if let scriptResult = runAppleScript("tell app \"Spotify\" to playpause") {
    NSLog("\(scriptResult)")
} else {
    print("no return value")
}

错误处理：

enum MyAppleScriptError: ErrorProtocol {
    case ExecutingScriptFailed
    case GettingStringValueFailed
}

func runAppleScript(_ script:String) throws -> String {
    let errorInfo: AutoreleasingUnsafeMutablePointer<NSDictionary?>? = nil
    let startAtLoginScript = NSAppleScript(source: script)
    guard let theDescriptor = startAtLoginScript?.executeAndReturnError(errorInfo) else {
        throw MyAppleScriptError.ExecutingScriptFailed
    }
    guard let value = theDescriptor.stringValue else {
        throw MyAppleScriptError.GettingStringValueFailed
    }
    return value
}

do {
    let scriptResult = try runAppleScript("tell app \"Spotify\" to playpause")
    NSLog("\(scriptResult)")
} catch {
    print(error)
}

Answer 2

我已经修复了我自己的代码。

import Foundation

func runAppleScript(script:String) -> String
{
    let theResult:String
    let errorInfo = AutoreleasingUnsafeMutablePointer<NSDictionary?>()
    let startAtLoginScript: NSAppleScript = NSAppleScript(source: script)!
    let theDiscriptor:NSAppleEventDescriptor = startAtLoginScript.executeAndReturnError(errorInfo)
    if let _ = theDiscriptor.stringValue
    {
        theResult = theDiscriptor.stringValue!
    } else {
        theResult = ""
    }

    return theResult
}



let scriptResult = runAppleScript("")

我必须做的是在展开之前检查 theDiscriptor.stringValue 是否有值。我得到的错误是因为我试图在打开它之后检查它的值。只需删除支票上的 ! 即可解决我的问题。

编辑

在 Swift 3 中尝试此操作时，代码 let errorInfo = AutoreleasingUnsafeMutablePointer<NSDictionary?>() 不再有效。为了解决这个问题，我更新了代码。

func runAppleScript(script:String) -> String?
{
    var theResult:String?
    let startAtLoginScript: NSAppleScript = NSAppleScript(source: script)!
    var errorInfo:NSDictionary? = nil
    let theDiscriptor:NSAppleEventDescriptor = startAtLoginScript.executeAndReturnError(&errorInfo)
    if let _ = theDiscriptor.stringValue {theResult = theDiscriptor.stringValue!}
    return theResult
}

奖金

通过返回一个可选字符串，它允许您检查代码是否返回了一个值。

示例：

老办法

let output = runAppleScript("script")
if output != ""
{
    //Script returned date
} else {
    //Script did not return data
}

新方式

if let output = runAppleScript("script")
{
    //Script returned data
} else {
    //Script did not return data
}

展开可选值时意外发现 nil（AppleScript 结果）

Unexpectedly found nil while unwrapping an Optional value (AppleScript result)

nsapplescript

swift

swift2