Swift4: `AXUIElementCopyAttributeValue()` returns `AXError.cannotComplete`

Question

On running the following code:

let pid = getAppPid()
let AXApp = AXUIElementCreateApplication(pid)

var children: CFTypeRef?
let returnVal = AXUIElementCopyAttributeValue(AXApp,
    kAXChildrenAttribute as CFString, &children)

• AXApp gets created successfully

However

• children is nil
• returnVal is AXError.cannotComplete ("A fundamental error has occurred, such as a failure to allocate memory during processing.")

I've seen code on stack overflow and elsewhere using exactly the same method as I am.

What am I missing.

I am using Xcode 9/Swift 4 on MacOS High Sierra.

EDIT:

I should add that Xcode has accessibility permissions, and I am able to successfully do other stuff that requires accessibility permission like CGEvent.tapCreate() to monitor global keyboard events etc.

Blakey

Switch off sandboxing. How to use Accessibility with sandboxed app? – Atlantis

Thanks, that works. If you add that as answer, I'll mark it as the right one. – Blakey

Also: I was able to get it working by setting the App Sandbox key to NO in the .entitlements file. I this the best way? I couldn't find a key to just request entitlement for accessibility, while preserving the rest of the sandbox compliance features. Do you know if some thing like that exists? Thanks. – Blakey

I don't know anything about App Sandbox. I managed to switch it off but that's it. – Atlantis

cool, I am doing the same. do you want to put your initial comment as an answer? – Blakey

Answer 1

To fix this error you should turn off App Sandbox by doing the following:

You can turn off Sandboxing by removing it from the Signing & Capabilities tab:

After that AXError.cannotComplete should not appear again. If you still get some issues you can try to get the selected text of the frontmost app like this:

import ApplicationServices
import Cocoa

func getSelectedText() -> String? {
    let systemWideElement = AXUIElementCreateSystemWide()

    var selectedTextValue: AnyObject?
    let errorCode = AXUIElementCopyAttributeValue(systemWideElement, kAXFocusedUIElementAttribute as CFString, &selectedTextValue)
    
    if errorCode == .success {
        let selectedTextElement = selectedTextValue as! AXUIElement
        var selectedText: AnyObject?
        let textErrorCode = AXUIElementCopyAttributeValue(selectedTextElement, kAXSelectedTextAttribute as CFString, &selectedText)
        
        if textErrorCode == .success, let selectedTextString = selectedText as? String {
            return selectedTextString
        } else {
            return nil
        }
    } else {
        print(errorCode.rawValue)
        return nil
    }
}

Tillich