// converting JSON Data to JSON String

// function call 

   self.deviceDict(2, mac: "22:00:88:p1:uu", sn: "123")

//---------------------------------------//

{
  "devices" : [
    {
      "id" : 2,
      "mac" : "22:00:88:p1:uu",
      "sn" : "123"
    }
  ]
}


//---------------------------------------//
 func  deviceDict(id:Int,mac:String,sn:String)-> String {
        
   let dict : NSMutableDictionary = NSMutableDictionary()
   let Arr : NSMutableArray = []
   let finaldict : NSMutableDictionary = NSMutableDictionary()
   dict.setValue(id, forKey: "id")
   dict.setValue(mac, forKey: "mac")
   dict.setValue(sn, forKey: "sn")
   Arr.addObject(dict)
        
  finaldict.setValue(Arr, forKey: "devices")
do {
   let jsonData : NSData = try! NSJSONSerialization.dataWithJSONObject(finaldict, options: NSJSONWritingOptions.PrettyPrinted)
            
   //Convert back to string. Usually only do this for debugging
  
   if let JSONString = String(data: jsonData, encoding: NSUTF8StringEncoding)
   {
      return JSONString

   }
            
 } // end of do
       
  return "Error"
        
}// end of function