#nsjsonserialization

JSON파일을 읽기 – Objective-C

Foundation에는 객체를 JSON 형식으로 직렬화하는 도구인 NSJSONSerialization를 제공한다. 이를 사용하면 객체 그래프를 JSON으로 변환하거나 반대로 JSON으로부터 객체 데이터를 재구성하여 사용할 수 있다. JSON 파일은 일반적인 텍스트 편집기로 열어볼 수 있는 텍스트 파일이지만, NSJSONSerialization은 파일을 읽어들인 바이트스트림을 객체로 변환한다. 따라서 파일은 NSData 형식으로 읽어들인 후에 사용하면 된다. 다음 예는 JSON 파일의 경로 문자열을 사용해 해당 위치의 파일을 읽어 사전으로 만드는 예를 보여준다. 주의할 것은 JSON 포맷은 기본적으로 키-값 쌍의 형태로 데이터를 맵핑하지만, 1차 레벨에서는 배열 형식의 객체일 수 있다. 따라서 JSON…

The following Swift snippet shows how to convert a string containing a JSON document into a JSON object (stored within an AnyObject or NSDictionary), and then separately how to extract the elements either walking through all the elements in a loop, or accessing specific elements within the JSON object. Pecularities about this solution:

Swift has no JSON object, rather you convert it to an AnyObject or NSDictionary using the NSJSONSerialization.JSONObjectWithData() call. This will validate the JSON structure during the serialization raising an error.

The NSJSonSerialization.JSONObjectWithData() options determines once the JSON AnyObject or NSDictionary is created, that the JSON objects is mutable or immutable. It's mutablility can be set through using options on the NSJSONReadingOptions object (e.g. NSJSONReadingOptions.AllFragments). To specify inmutability the options is set to nil.

Note odd use of & on the error parameter in call to JSONObjectWithData. Don't get confused with the C++ convention for passing in by-reference-variables rather than the pointer. Rather this is a Swift inout parameter on the function, and the ambersand is the syntax for indicating that to the caller.

If you place the JSON object into an NSDictionary, the JSON elements are automatically sorted.

When extracting values (of key-value pairs) from the JSON object, boolean values are integers rather than the Boolean type.

When extracting values (of key-value pairs), some care needs to be given to what happens if there is a potential for value to be an empty array or null. If you know the value is mandatory this can be safetly ignored such as firstName in the JSON example below, but the children and spouse keys are an empty array and null respectively which requires guarded statements to be written.

Ever since iOS5, the iOS supports the JSON parsing API. The NSJSONSerialization Class could convert JSON to Foundation objects, and convert Foundation objects to JSON. The Foundation objects supported in the API are NSDictionary, NSArray, NSString, NSNumber. (Checkout the Document for detail.)

So, making a HTTP Request on iOS, it requires a NSURLRequest(HTTP Request) configured appropriately, and the NSData to be sent to the server.

1st, Construct the NSData.

NSMutableDictionary *json = [[NSMutableDictionary alloc] init]; [json setValue:[NSString stringWithFormat:@"%d", 2] forKey:@"user_id"];

This piece of code would have a NSDictionary ready with Keys & Values.

NSError *e = nil; if (![NSJSONSerialization isValidJSONObject:json]) { NSLog(@"Invalid JSON format Data"); return nil; }

This piece checks if our constructed data is valid to be a JSON object to be converted.

NSData *data = [NSJSONSerialization dataWithJSONObject:json options:0 error:&e];

Then, this NSData object data is the data we will need to send to the server.

2nd, Configure the NSURLRequest

//1, Create NSURLSession. NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration] delegate:nil delegateQueue:nil]; //2, Create NSURLRequest NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:@"http://localhost:4730/adddata"]]; // 3, Configure the Method of HTTP Request. [request setHTTPMethod:@"POST"]; // 3, Configure the Body(Data) of HTTP Request. [request setHTTPBody:[self postData]]; // 3, Configure the Header of HTTP Request. [request setValue:@"application/json" forHTTPHeaderField:@"Content-Type"]; // 4, Create DataTask with Callback function(Block) in it. The block will be fired once the server returns any data to the request. NSURLSessionDataTask *sessionDataTask = [session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) { if (error) { // Handle the error; NSLog(@"Error: %@", error.localizedDescription); } NSDictionary* json = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error]; NSLog(@"Error: %@", error.localizedDescription); NSLog(@"Response POST: %@", json); dispatch_async(dispatch_get_main_queue(), ^{ self.display.text = [NSString stringWithFormat:@"%@\n%@", json, self.display.text]; }); }]; // 5, Fire the DataTask [sessionDataTask resume];

Here, the code

1st, Create a NSURLSession, which will generate a URLTask based on the URLRequest created later.

2nd, Create a NSURLRequest. Since we need to configure the request, then we make it mutable here. The exact URL is the string url, to which is the Restful API of the server.

3rd, Configure the Request with Method, Body(Data) and HTTPHeader.

4th, Create a DataTask which accomplishes the actual request operation. It has a Callback(Block) in it, which will be fired once the request accomplished, data will be received if the server returns any data, like confirmation data, etc.

json string to NSArray or NSDictionary

NSString *jsonString = @"[{\"id\": \"1\", \"name\":\"Aaa\"}, {\"id\": \"2\", \"name\":\"Bbb\"}]";

NSData *jsonData = [jsonString dataUsingEncoding:NSUTF8StringEncoding];

NSError *err = nil;

NSMutableArray *arr = [NSJSONSerialization JSONObjectWithData:jsonData options:NSJSONReadingMutableContainers error:&err];

NSArray or NSDictionary to json string

NSData *jsonData = [NSJSONSerialization dataWithJSONObject:myNSMutableArray options:NSJSONWritingPrettyPrinted error:nil];