Crash When Clicking on Definition View Created by AppKit's showDefinition(for:at)

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Created Mar ’24

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I'm encountering a crash issue in my macOS application when clicking on the view generated by AppKit's showDefinition(for:at) function. I'm seeking assistance to resolve this issue.

**Problem Description: **

I'm developing a macOS application where I utilize the showDefinition(for:at) function provided by AppKit to display the definition view of words. However, whenever I click on this view, the application crashes abruptly.

**Error Message: **

The crash log reveals the following error message:

Fault: deferNSXPCInvocationOntoMainThread_block_invoke caught NSInternalInconsistencyException '_CPSSetFrontProcessWithOptions failed due to CGError -606 4294966690 fffffda2 (appIsDaemon)'

Attempts Made:

Tried wrapping relevant code blocks with DispatchQueue.main.async, suspecting a threading issue.

Making the DefinitionWindow variable a global one to manually control its lifecycle

Development Environment:

macOS Version: 14.3.1 Xcode Version: 15

Below is a complete and reproducible code snippet that can be directly executed within a terminal project template. Please note that it requires Accessibility permissions to be granted in the Privacy settings.

import Cocoa
import SwiftUI
import AppKit

class AppDelegate: NSObject, NSApplicationDelegate {
    func applicationDidFinishLaunching(_ notification: Notification) {
        NSEvent.addGlobalMonitorForEvents(matching: .keyDown) { [weak self] event in
            guard let self = self else { return }
            if event.modifierFlags.contains(.command) && event.charactersIgnoringModifiers == "c" {
                self.ShowWordDefinition()
            }
        }
        NSApp.servicesProvider = self
        NSApp.registerServicesMenuSendTypes([.string], returnTypes: [])
    }
    func ShowWordDefinition(){
        DispatchQueue.main.asyncAfter(deadline: .now() + 0.1) {
            let attributedString = NSAttributedString(string:NSPasteboard.general.string(forType: .string)!)
            let DefinitionWindow = NSWindow(contentRect: NSRect(origin: .zero, size: NSSize(width: 1, height: 1)), styleMask: [.borderless], backing: .buffered, defer: false)
            // on the top
            DefinitionWindow.level = .floating
            let pointInWindow = NSPoint(x:0,y:0); //default value
            DefinitionWindow.contentView?.showDefinition(for: attributedString, at: pointInWindow)
            DefinitionWindow.orderFront(nil)
        }
    }
}
let delegate = AppDelegate()
let app = NSApplication.shared
app.delegate = delegate
app.run()

full crash log reveals the following error message:

FAULT: deferNSXPCInvocationOntoMainThread_block_invoke caught NSInternalInconsistencyException '_CPSSetFrontProcessWithOptions failed due to CGError -606 4294966690 fffffda2 (appIsDaemon)' with backtrace (
    "0   CoreFoundation                      __exceptionPreprocess + 176",
    "1   libobjc.A.dylib                     objc_exception_throw + 60",
    "2   CoreFoundation                      +[NSException exceptionWithName:reason:userInfo:] + 0",
    "3   ViewBridge                          assertCGError + 80",
    "4   ViewBridge                          -[NSRemoteView _serviceWindowWouldActivate] + 724",
    "5   CoreFoundation                      __invoking___ + 148",
    "6   CoreFoundation                      -[NSInvocation invoke] + 428",
    "7   ViewBridge                          __deferNSXPCInvocationOntoMainThread_block_invoke + 120",
    "8   ViewBridge                          __wrapBlockWithVoucher_block_invoke + 56",
    "9   ViewBridge                          deferredBlockOpportunity_block_invoke_2 + 360",
    "10  CoreFoundation                      __CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__ + 28",
    "11  CoreFoundation                      __CFRunLoopDoBlocks + 356",
    "12  CoreFoundation                      __CFRunLoopRun + 2440",
    "13  CoreFoundation                      CFRunLoopRunSpecific + 608",
    "14  HIToolbox                           RunCurrentEventLoopInMode + 292",
    "15  HIToolbox                           ReceiveNextEventCommon + 648",
    "16  HIToolbox                           _BlockUntilNextEventMatchingListInModeWithFilter + 76",
    "17  AppKit                              _DPSNextEvent + 660",
    "18  AppKit                              -[NSApplication(NSEventRouting) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 716",
    "19  AppKit                              -[NSApplication run] + 476",
    "20  try                                 main + 160",
    "21  dyld                                start + 2360"
)

Just a reminder, the application will crash when you click on the displayed definition window.

Potential Questions and Concerns:

Could there be an issue related to UI transitions or the main thread?

How exactly does the showDefinition(for:at) process work internally?

Maybe , the view's display level being raised when clicked caused conflict?

If anyone could provide any insights or guidance on resolving this issue, it would be greatly appreciated. Thank you!

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