Catch Objective-C exception in Swift

Question

I am trying to set the value of an @objc object in my Swift code using obj.setValue(value, forKey: key).

It works fine when the object has the property being set. But if it doesn't, my app crashes hard with an uncaught NSException ("class is not key value coding-compliant…").

How can I catch and absorb this exception like I can in Objective-C so as to not crash my app? I tried wrapping it in a Swift try-catch, but it complains that none of the instructions throws and does nothing.

Answer 1

see this answer:

//
//  ExceptionCatcher.h
//

#import <Foundation/Foundation.h>    

NS_INLINE NSException * _Nullable tryBlock(void(^_Nonnull tryBlock)(void)) {
    @try {
        tryBlock();
    }
    @catch (NSException *exception) {
        return exception;
    }
    return nil;
}

Answer 2

Not the answer I was hoping for, unfortunately:

Although Swift error handling resembles exception handling in Objective-C, it is entirely separate functionality. If an Objective-C method throws an exception during runtime, Swift triggers a runtime error. There is no way to recover from Objective-C exceptions directly in Swift. Any exception handling behavior must be implemented in Objective-C code used by Swift.

Excerpt From: Apple Inc. “Using Swift with Cocoa and Objective-C (Swift 2.1).” iBooks. https://itun.es/ca/1u3-0.l

My next plan of attack is to add an Objective-C function I can call out to that will wrap the attempt in @try/@catch. This really sucks, Apple.

Answer 3

I wanted to call out the answer given in this question:

Catching NSException in Swift

as you can still use the Swift do/catch with the call in a natural fashion, the next best thing to Swift actually catching ObjC exceptions as it should.