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iOS Error Handling in Swift Error Handling Handling Errors

Posted by Tim Watkins
Tim Watkins
16,034 Points

Need help with errors

enum ParserError: Error { case emptyDictionary case invalidKey }

struct Parser { var data: [String : String?]?

func parse() throws {
    guard let dict = data else { throw ParserError.emptyDictionary }
    guard dict.keys.contains("someKey") else { throw ParserError.invalidKey }

}

let data: [String : String?]? = ["someKey": nil] let parser = Parser(data: data)

do { let parsed = try parser.parse() } catch ParserError.emptyDictionary { print("Empty Dictionary!") } catch ParserError.invalidKey { print("Invalid Key!") }

error.swift 
enum ParserError: Error {
    case emptyDictionary
    case invalidKey
}

struct Parser {
    var data: [String : String?]?

    func parse() throws {
        guard let dict = data else { throw ParserError.emptyDictionary }
        guard dict.keys.contains("someKey") else { throw ParserError.invalidKey }
}

let data: [String : String?]? = ["someKey": nil]
let parser = Parser(data: data)

do {
    let parsed = try parser.parse()
} catch ParserError.emptyDictionary {
    print("Empty Dictionary!")
} catch ParserError.invalidKey {
    print("Invalid Key!")
}

1 Answer

Aniruddha Shukla
Aniruddha Shukla
2,846 Points
Aniruddha Shukla
Aniruddha Shukla
2,846 Points

I would refine your try catch block. You can declare your constant error in the catch block. Something like this

do {
    try parser.parse()
} catch(let error) {
    switch error {
    case ParserError.emptyDictionary:
        print("Empty Dictionary")
    case ParserError.invalidKey:
        print("Invalid Key")
    default:
        print("Some other error")
    }

}
Tim Watkins
Tim Watkins
16,034 Points

Awesome! Thanks that works