I have an app whose logic is in C++ and rest of the parts (UI) are in Swift and SwiftUI.
Exceptions can occur in C++ and Swift. I've got the C++ part covered by using the Linux's signal handler mechanism to trap signals which get raised due to exceptions.
But how should I capture exceptions in Swift? When I say exceptions in Swift, I mean, divide by zero, force unwrapping of an optional containing nil, out of index access in an array, etc. Basically, anything that can go wrong, I don't want my app to abruptly crash... I need a chance to finalise my stuff, alert the user, prepare diagnostic reports and terminate. I'm looking for a 'catch-all' exception handler. As an example, let's take Android. In Android, there is the setDefaultUncaughtExceptionHandler method to register for all kinds of exceptions in any thread in Kotlin. I'm looking for something similar in Swift that should work for macOS, iOS & iPadOS, tvOS and watchOS.
I first came across the NSSetUncaughtExceptionHandler method. My understanding is, this only works when I explicitly raise NSExceptions. When I tested it, observed that the exception handler didn't get invoked for either case - divide by zero or invoking raise.
class AppDelegate: NSObject, NSApplicationDelegate {
func applicationDidFinishLaunching(_ aNotification: Notification) {
Log("AppDelegate.applicationDidFinishLaunching(_:)")
// Set the 'catch-all' exception handler for Swift exceptions.
Log("Registering exception handler using NSSetUncaughtExceptionHandler()...")
NSSetUncaughtExceptionHandler { (exception: NSException) in
Log("AppDelegate.NSUncaughtExceptionHandler()")
Log("Exception: \(exception)")
}
Log("Registering exception handler using NSSetUncaughtExceptionHandler() succeeded!")
// For C++, use the Linux's signal mechanism.
ExceptionHandlingCpp.RegisterSignals()
//ExceptionHandlingCpp.TestExceptionHandler()
AppDelegate.TestExceptionHandlerSwift()
}
static func TestExceptionHandlerSwift() {
Log("AppDelegate.TestExceptionHandlerSwift()")
DivisionByZero(0)
}
private static func DivisionByZero(_ divisor: Int) {
Log("AppDelegate.DivisionByZero()")
let num1: Int = 2
Log("Raising Exception...")
//let result: Int = num1/divisor
let exception: NSException = NSException(name: NSExceptionName(rawValue: "arbitrary"), reason: "arbitrary reason", userInfo: nil)
exception.raise()
Log("Returning from DivisionByZero()")
}
}
In the above code, dividing by zero, nor raising a NSException invokes the closure passed to NSSetUncaughtExceptionHandler, evident from the following output logs
AppDelegate.applicationWillFinishLaunching(_:)
AppDelegate.applicationDidFinishLaunching(_:)
Registering exception handler using NSSetUncaughtExceptionHandler()...
Registering exception handler using NSSetUncaughtExceptionHandler() succeeded!
ExceptionHandlingCpp::RegisterSignals()
....
AppDelegate.TestExceptionHandlerSwift()
AppDelegate.DivisionByZero()
Raising Exception...
Currently, I'm reading about ExceptionHandling framework, but this is valid only for macOS.
What is the recommended way to capture runtime issues in Swift?
