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

Question

I am trying to make a program in Swift 2 that runs and gets the result of an AppleScript script.
Here is my code:
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)")
The problem is the program crashes and outputs:
fatal error: unexpectedly found nil while unwrapping an Optional value
in the console. I have also tried if let else, however that does not work either. How would I fix this issue?
This was tested using a OS X Command Line template using the swift language.

Answer 1

Actually the error could come from NSAppleScript(source: script)! so the proper solution is to return an Optional String and not use force unwrapping at all:
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")
}
If you prefer having a default value instead of nil when it fails, then no need to return an Optional:
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)")
As for using the new Swift 2 error handling system, none of the methods you're using inside runAppleScript are throwing errors, so it would only work if you used a custom error type and throw the errors yourself. Example:
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
Same idea, but some implementation details are different.
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")
}
And with error handling:
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

I have fixed my own code.
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("")
What I had to do was check if theDiscriptor.stringValue has a value before unwrapping it. The error that I was getting is because I was trying to check the value after I had unwrapped it. Simply removing the ! on the check fixed my problem.
Edit
When trying this in Swift 3, the code let errorInfo = AutoreleasingUnsafeMutablePointer<NSDictionary?>() no longer works. To fix this, I have updated the code.
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
}
Bonus
By returning an optional string, it allows you to check if the code returned a value.
Example:
Old way
let output = runAppleScript("script")
if output != ""
{
//Script returned date
} else {
//Script did not return data
}
New way
if let output = runAppleScript("script")
{
//Script returned data
} else {
//Script did not return data
}