NSJSONReadingMutableContainers
Specifies that arrays and dictionaries are created as mutable objects. // 创建可变的数组或字典 接收
NSJSONReadingMutableLeaves
Specifies that leaf strings in the JSON object graph are created as instances of NSMutableString. // 指定在JSON对象可变字符串被创建为NSMutableString的实例
NSJSONReadingAllowFragments
Specifies that the parser should allow top-level objects that are not an instance of NSArray
or NSDictionary // 指定解析器应该同意不属于的NSArray或NSDictionary中的实例顶层对象
測试的
每一项都用字典接收，系统也没有给我报错。
难道这是给返回的data类型有关，假设返回的是字典或数组。就用第一项