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.

Sorry thats a typo, it actually should be parseString..i was doing some changes, forgot to change that — ash007
– ash007, Commented Jan 5, 2017 at 6:31
Please take the time and check that your code at least compiles before posting it (there is no void in Swift). — Martin R
– Martin R, Commented Jan 5, 2017 at 6:35

Trond · Accepted Answer · 2017-01-05 08:08:13Z

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

Satyanarayana · Accepted Answer · 2017-01-05 07:49:12Z

0

Hi you wrote nested function means it will available within the scope of that function only, you need to call that nested function it is wirked as loop with condition , i given some example here once check

static func normalFunction(value: Int) -> Int {
    var valueTemp = value;
    func nestedFunction() -> Int {
        valueTemp = valueTemp * 20
        return valueTemp
    }
    if value % 2 == 0 {
        valueTemp = nestedFunction() //nested function calling 
    }
    return valueTemp
}

answered Jan 5, 2017 at 7:49

Satyanarayana

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