iOS字典转字符串类型，NSDictionary 转 NSString转JsonData

1.字典

 NSDictionary* paramDic =@{@"username":username,

                             @"password":[selfmd5PasswordWithPassword:password],

                              @"userInfo":@{@"source":@"mode"}};

 2.转jsonData

 NSData *jsonData = [NSJSONSerializationdataWithJSONObject:paramDic options:NSJSONWritingPrettyPrintederror:nil];

3.jsonData转NSString

NSString* jsonStr = [[NSStringalloc]initWithData:jsonDataencoding:NSUTF8StringEncoding];