Catching NSException in Swift

Question

The following code in Swift raises NSInvalidArgumentException exception:

task = NSTask() task.launchPath = "/SomeWrongPath" task.launch() 

How can I catch the exception? As I understand, try/catch in Swift is for errors thrown within Swift, not for NSExceptions raised from objects like NSTask (which I guess is written in ObjC). I'm new to Swift so may be I'm missing something obvious...

Edit: here's a radar for the bug (specifically for NSTask): openradar.appspot.com/22837476

Answer 1

Here is some code, that converts NSExceptions to Swift 2 errors.

Now you can use

do {     try ObjC.catchException {         /* calls that might throw an NSException */     } } catch {     print("An error ocurred: \(error)") } 

ObjC.h:

#import <Foundation/Foundation.h>  @interface ObjC : NSObject  + (BOOL)catchException:(void(^)(void))tryBlock error:(__autoreleasing NSError **)error;  @end 

ObjC.m

#import "ObjC.h"  @implementation ObjC   + (BOOL)catchException:(void(^)(void))tryBlock error:(__autoreleasing NSError **)error {     @try {         tryBlock();         return YES;     }     @catch (NSException *exception) {         *error = [[NSError alloc] initWithDomain:exception.name code:0 userInfo:exception.userInfo];         return NO;     } }  @end 

Don't forget to add this to your "*-Bridging-Header.h":

#import "ObjC.h" 

Answer 2

What I suggest is to make an C function that will catch the exception and return a NSError instead. And then, use this function.

The function could look like this:

NSError *tryCatch(void(^tryBlock)(), NSError *(^convertNSException)(NSException *)) {     NSError *error = nil;     @try {         tryBlock();     }     @catch (NSException *exception) {         error = convertNSException(exception);     }     @finally {         return error;     } } 

And with a little bridging help, you'll just have to call:

if let error = tryCatch(task.launch, myConvertFunction) {     print("An exception happened!", error.localizedDescription)     // Do stuff } // Continue task 

Note: I didn't really test it, I couldn't find a quick and easy way to have Objective-C and Swift in a Playground.