NSURLSession 使用範例：

NSMutableURLRequest *urlRequest = [[NSMutableURLRequest alloc] initWithURL:[NSURL URLWithString:@"give your url here"]];

//create the Method "GET" 
[urlRequest setHTTPMethod:@"GET"];

NSURLSession *session = [NSURLSession sharedSession];

NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:urlRequest completionHandler:^(NSData *data, NSURLResponse *response, NSError *error)
{
  NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
  if(httpResponse.statusCode == 200)
  {
    NSError *parseError = nil;
    NSDictionary *responseDictionary = [NSJSONSerialization JSONObjectWithData:data options:0 error:&parseError];
    NSLog(@"The response is - %@",responseDictionary);
  }
  else
  {
    NSLog(@"Error");     
  }
}];
[dataTask resume];

Handle HTTP error with NSURLSession?

NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:[self postRequestWithURLString:apiEntry parameters:parameters] completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {

    // handle basic connectivity issues here

    if (error) {
        NSLog(@"dataTaskWithRequest error: %@", error);
        return;
    }

    // handle HTTP errors here

    if ([response isKindOfClass:[NSHTTPURLResponse class]]) {

        NSInteger statusCode = [(NSHTTPURLResponse *)response statusCode];

        if (statusCode != 200) {
            NSLog(@"dataTaskWithRequest HTTP status code: %d", statusCode);
            return;
        }
    }

    // otherwise, everything is probably fine and you should interpret the `data` contents

    NSLog(@"data: %@", [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding]);
}];
[dataTask resume];

Sample 2:

// 1
NSURL *url = [NSURL URLWithString:@"YOUR_WEBSERVICE_URL"];
NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
NSURLSession *session = [NSURLSession sessionWithConfiguration:config];

// 2
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:url];
request.HTTPMethod = @"POST";

// 3
NSDictionary *dictionary = @{@"key1": @"value1"};
NSError *error = nil;
NSData *data = [NSJSONSerialization dataWithJSONObject:dictionary 
  options:kNilOptions error:&error];

if (!error) {
 // 4
 NSURLSessionUploadTask *uploadTask = [session uploadTaskWithRequest:request
   fromData:data completionHandler:^(NSData *data,NSURLResponse *response,NSError *error) {
   // Handle response here
   }];

   // 5
   [uploadTask resume];
}

Convert UTF-8 encoded NSData to NSString

NSString* newStr = [[NSString alloc] initWithData:theData encoding:NSUTF8StringEncoding];

NSString* newStr = [NSString stringWithUTF8String:[theData bytes]];

let newStr = String(data: data, encoding: .utf8)
// note that `newStr` is a `String?`, not a `String`.

// safe way, provided data is 
// safe way, provided data is \0-terminated
let newStr1 = String(data: data.subdata(in: 0 ..< data.count - 1), encoding: .utf8)
// unsafe way, provided data is \0-terminated
let newStr2 = data.withUnsafeBytes(String.init(utf8String:))
-terminated
let newStr1 = String(data: data.subdata(in: 0 ..< data.count - 1), encoding: .utf8)
// unsafe way, provided data is 
// safe way, provided data is \0-terminated
let newStr1 = String(data: data.subdata(in: 0 ..< data.count - 1), encoding: .utf8)
// unsafe way, provided data is \0-terminated
let newStr2 = data.withUnsafeBytes(String.init(utf8String:))
-terminated
let newStr2 = data.withUnsafeBytes(String.init(utf8String:))