Return function from a function in Objective C?

Question

I am using this swift function inside my objective c project to parse a JSON, this function looks like this: (This function is inside NetworkService class)

static func parseJSONString(jsonString: String?, key: String?) -> () -> String{
    var jsonSubString = String()
    func parseString() -> String{
        if let data = jsonString?.data(using: .utf8){
            if let content = try? JSONSerialization.jsonObject(with: data, options: []),
                let array = content as? [[String: AnyObject]]
            {

                for jsondict in array {
                    jsonSubString = jsondict[key!] as! String
                }
            }
        }
        return jsonSubString
    }
    return parseString
}

I want to call this function inside ViewController which is Objective C. It is a static method. Please help me in calling this function.

Answer 1

You have to expose the function to Objective-C.

If your class is not already exposed to Objective-C you have to mark it with the @objc directive and inherit from NSObject, like this:

@objc class NetworkService: NSObject {

    static func parseJSONString(jsonString: String?, key: String?) -> () -> String{
        var jsonSubString = String()
        func parseString() -> String{
            if let data = jsonString?.data(using: .utf8){
                if let content = try? JSONSerialization.jsonObject(with: data, options: []),
                    let array = content as? [[String: AnyObject]]
                {

                    for jsondict in array {
                        jsonSubString = jsondict[key!] as! String
                    }
                }
            }
            return jsonSubString
        }
        return parseString
    }
}

Then in Objective-C you include the swift-generated header (I recommend including it in the .m-file), which is usually named [your-product-name-here]-Swift.h

You now should be able to call your function from Objective-C like this:

NSString* (^parseJson)(void) = [NetworkService parseJSONStringWithJsonString:@"SomeString" key:@"SomeOtherString"];
NSString* result = parseJson();

or simply like this:

NSString* otherResult = [NetworkService parseJSONStringWithJsonString:@"SomeString"
                                                                  key:@"SomeOtherString"]();

More on this in documentation from Apple here