在ios開發過程中，可能會遇到需要將字符串類型的數據轉換為字典類型的數據，做法是借助中間類NSData進行轉換。
1.將字符串類型轉換為NSData
NSData *jsonData = [jsonString dataUsingEncoding:NSUTF8StringEncoding];
2.將NSData解析為NSDictionary
NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:jsonData
options:NSJSONReadingMutableContainers
error:nil];
/* Create a Foundation object from JSON data. Set the NSJSONReadingAllowFragments option if the parser should allow top-level objects that are not an NSArray or NSDictionary. Setting the NSJSONReadingMutableContainers option will make the parser generate mutable NSArrays and NSDictionaries. Setting the NSJSONReadingMutableLeaves option will make the parser generate mutable NSString objects. If an error occurs during the parse, then the error parameter will be set and the result will be nil.
The data must be in one of the 5 supported encodings listed in the JSON specification: UTF-8, UTF-16LE, UTF-16BE, UTF-32LE, UTF-32BE. The data may or may not have a BOM. The most efficient encoding to use for parsing is UTF-8, so if you have a choice in encoding the data passed to this method, use UTF-8.
*/
這是官網上對json解析函數JSONObjectWithData參數的解釋。
這個函數返回一個id類型的對象，options參數是NSJSONReadingAllowFragments返回不可變數組或字典，當options參數是NSJSONReadingMutableContainers返回可變數組或字典，當options參數是NSJSONReadingMutableLeaves時，返回NSString類型。json支持5種編碼方式， UTF-8, UTF-16LE, UTF-16BE, UTF-32LE, UTF-32BE，官方推薦UTF-8。