Catch an exception for invalid user input in swift
cocoa-touch, exception, ios, nsexpression, swift
Solution
This is still an issue in Swift 2. As noted, the best solution is to use a bridging header and catch the NSException in Objective C.
https://medium.com/swift-programming/adding-try-catch-to-swift-71ab27bcb5b8 describes a good solution, but the exact code doesn't compile in Swift 2 because `try` and `catch` are now reserved keywords. You'll need to change the method signature to workaround this. Here's an example:
// https://medium.com/swift-programming/adding-try-catch-to-swift-71ab27bcb5b8
@interface TryCatch : NSObject
+ (void)tryBlock:(void (^)())try catchBlock:(void (^)(NSException *))catch finallyBlock:(void (^)())finally;
@end
@implementation TryCatch
+ (void)tryBlock:(void (^)())try catchBlock:(void (^)(NSException *))catch finallyBlock:(void (^)())finally {
@try {
try ? try() : nil;
}
@catch (NSException *e) {
catch ? catch(e) : nil;
}
@finally {
finally ? finally() : nil;
}
}
@end
Problem
I am trying this code that is a calculator. How can I handle input from the user that is not valid? //ANSWER: Bridging header to Objective-C// https://github.com/kongtomorrow/TryCatchFinally-Swift Here is the same question but in objc but I want to do this in swift. Catching NSInvalidArgumentException from NSExpression All I want to show is a message if it doesn't work, but now I am getting an exception when the user doesn't input the correct format. ``` import Foundation var equation:NSString = "60****2" // This gives a NSInvalidArgumentException', let expr = NSExpression(format: equation) // reason: 'Unable to parse the format string if let result = expr.expressionValueWithObject(nil, context: nil) as? NSNumber { let x = result.doubleValue println(x) } else { println("failed") } ```