数组、字典转json格式字符串

1. #pragma mark--把字典和数组转换成json字符串  
2. +(NSString *)stringTOjson:(id)obj   //把字典和数组转换成json字符串  
3. {  
4.     NSData* jsonData =[NSJSONSerialization dataWithJSONObject:obj  
5.                                                       options:NSJSONWritingPrettyPrinted error:nil];  
6.     NSString *strs=[[NSString alloc] initWithData:jsonData  
7.                                          encoding:NSUTF8StringEncoding];  
8.     return strs;  
9. }