Swift JSON解析-无法访问字段/返回nil

Question

I'm using Google's geolocator API to map some stuff automatically. It returns a JSON string in the request, but I'm having a lot of difficulty parsing it. I've tried things like Freddy and SwiftyJSON but can't get either to extract the field I want.

Here's a sample of my code:

func sendJsonRequest(ConnectionString: String,
                              HTTPMethod : HttpMethod = HttpMethod.Get,
                              JsonHeaders : [String : String] = [ : ],
                              JsonString: String = "") -> NSData? {

    // create the request & response
    let request = NSMutableURLRequest(URL: NSURL(string: ConnectionString)!, cachePolicy: NSURLRequestCachePolicy.ReloadIgnoringLocalCacheData, timeoutInterval: 5)

    // create some JSON data and configure the request
    let jsonString = JsonString;
    request.HTTPBody = jsonString.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: true)

    // handle both get and post
    request.HTTPMethod = HTTPMethod.rawValue

    // we'll always be sending json so this is fine
    request.setValue("application/json", forHTTPHeaderField: "Content-Type")

    // add the headers.  If there aren't any then that's ok
    for item in JsonHeaders {
        request.addValue(item.1, forHTTPHeaderField: item.0)
    }
    print("Request:")
    print(request)

    let session = NSURLSession.sharedSession()
    var data : NSData?

    var urlTask = session.dataTaskWithRequest(request) { (Data, Response, Error) in
        data = Data
    }
    urlTask.resume()

    while (data == nil) {

    }

    return data

}

// return the coordinates of a given location
func getCoordinates() -> Coordinates {
    var result = Coordinates()

    let ConnectionString = "https://maps.googleapis.com/maps/api/geocode/json?address=43201"
    let jsondata = sendJsonRequest(ConnectionString)

    let data = jsondata

    let json = JSON(data!)

    print(json)


    return result
}

getCoordinates()

Here's an example of the output I'm getting from a separate JSON client:

{
"results": [
    {
        "address_components": [
            {
                "long_name": "43201",
                "short_name": "43201",
                "types": [
                    "postal_code"
                ]
            },
            {
                "long_name": "Columbus",
                "short_name": "Columbus",
                "types": [
                    "locality",
                    "political"
                ]
            },
            {
                "long_name": "Franklin County",
                "short_name": "Franklin County",
                "types": [
                    "administrative_area_level_2",
                    "political"
                ]
            },
            {
                "long_name": "Ohio",
                "short_name": "OH",
                "types": [
                    "administrative_area_level_1",
                    "political"
                ]
            },
            {
                "long_name": "United States",
                "short_name": "US",
                "types": [
                    "country",
                    "political"
                ]
            }
        ],
        "formatted_address": "Columbus, OH 43201, USA",
        "geometry": {
            "bounds": {
                "northeast": {
                    "lat": 40.011147,
                    "lng": -82.9723898
                },
                "southwest": {
                    "lat": 39.976962,
                    "lng": -83.0250691
                }
            },
            "location": {
                "lat": 39.9929821,
                "lng": -83.00122100000002
            },
            "location_type": "APPROXIMATE",
            "viewport": {
                "northeast": {
                    "lat": 40.011147,
                    "lng": -82.9723898
                },
                "southwest": {
                    "lat": 39.976962,
                    "lng": -83.0250691
                }
            }
        },
        "place_id": "ChIJ9Rz24rWOOIgR3EEuL2Ge4oo",
        "types": [
            "postal_code"
        ]
    }
],
"status": "OK"
}

I'm trying to get the field results.geometry.location. Using the Freddy JSON parsing library I was able to get the results field but I couldn't access the geometry field. Can someone take a look at this to see if I'm doing something wrong? SwiftyJSON doesn't even let me parse the JSON.

Answer 1

The closure passed as an argument in dataTaskWithRequest is asynchronous meaning that it could be called instantly or way down the road given network conditions. It would be better to pass a closure in your original sendJsonRequest method while return void . Once the dataTaskWithResult closure is called, you can invoke your closure with the response.

In terms of code, it might look like this:

func sendJsonRequest(connectionString: String,
                              httpMethod : HttpMethod = HttpMethod.Get,
                              jsonHeaders : [String : String] = [ : ],
                              jsonString: String = "",
                              completion: (data: NSData?, error: NSError?) -> Void) {
   … //Your code
    var urlTask = session.dataTaskWithRequest(request) { (optionalData, optionalResponse, optionalError) in
        NSOperationQueue.mainQueue().addOperation {
            if let data = optionalData {
            completion(data, nil)
            }
            else if let error = optionalError {
            completion(nil, error)
            }
        }
    }
    urlTask.resume()
}

// return the coordinates of a given location
func getCoordinates(withCompletion completion: (Coordinates) -> Void) {

    let connectionString = "https://maps.googleapis.com/maps/api/geocode/json?address=43201"
    sendJsonRequest(connectionString: connectionString) {
        (optionalData, optionalError) in
        if let data = optionalData {
            let json = JSON(data)
            print(json)
            //Do your conversion to Coordinates here
            let coordinates = //?
            completion(coordinates)
        }
        // Handle errors, etc…
    }
}

One note, arguments and variables are lowercased. Only class names should be uppercase.

Answer 2

It's a javascript object, you can do the below to retrive information

Assign the result to a variable

var results = {
"results": [
    {
        "address_components": [
            {
                "long_name": "43201",
                "short_name": "43201",
                "types": [
                    "postal_code"
                ]
            },
            {
                "long_name": "Columbus",
                "short_name": "Columbus",
                "types": [
                    "locality",
                    "political"
                ]
            },
            {
                "long_name": "Franklin County",
                "short_name": "Franklin County",
                "types": [
                    "administrative_area_level_2",
                    "political"
                ]
            },
            {
                "long_name": "Ohio",
                "short_name": "OH",
                "types": [
                    "administrative_area_level_1",
                    "political"
                ]
            },
            {
                "long_name": "United States",
                "short_name": "US",
                "types": [
                    "country",
                    "political"
                ]
            }
        ],
        "formatted_address": "Columbus, OH 43201, USA",
        "geometry": {
            "bounds": {
                "northeast": {
                    "lat": 40.011147,
                    "lng": -82.9723898
                },
                "southwest": {
                    "lat": 39.976962,
                    "lng": -83.0250691
                }
            },
            "location": {
                "lat": 39.9929821,
                "lng": -83.00122100000002
            },
            "location_type": "APPROXIMATE",
            "viewport": {
                "northeast": {
                    "lat": 40.011147,
                    "lng": -82.9723898
                },
                "southwest": {
                    "lat": 39.976962,
                    "lng": -83.0250691
                }
            }
        },
        "place_id": "ChIJ9Rz24rWOOIgR3EEuL2Ge4oo",
        "types": [
            "postal_code"
        ]
    }
],
"status": "OK"
};



console.log(results); // you can see the object
Object {results: Array[1], status: "OK"}
console.log(results.results[0]); // Accessing the first object inside the array
Object {address_components: Array[5], formatted_address: "Columbus, OH 43201, USA", geometry: Object, place_id: "ChIJ9Rz24rWOOIgR3EEuL2Ge4oo", types: Array[1]}
console.log(results.results[0].geometry); // Accessing the geometry object.
Object {bounds: Object, location: Object, location_type: "APPROXIMATE", viewport: Object}

you can use JSON.stringify to make it simple.

Answer 3

I got my code to work with the Freddy JSON library. Here's my new code, in case anyone runs into a similar issue:

func getCoordinates(address: String) -> Coordinates {
    var result = Coordinates()

    let ConnectionString = _connectionUrl + address
    let jsondata = sendJsonRequest(ConnectionString)

    //print(json)
    // returns a [string : AnyObject]
    let data = jsondata
    do {
        let json = try JSON(data: data!)
        let results = try json.array("results")[0]

        let geometry = try results.dictionary("geometry")
        print(geometry)
        let location = geometry["location"]!

        print(location)
        let lat = try location.double("lat")
        let lng = try location.double("lng")

        result.Latitude = lat
        result.Longitude = lng

    } catch {
        let nsError = error as NSError
        print(nsError.localizedDescription)
    }
}