一 jsonstring 转化为object类
NSString *jsonStr = @"..........";
NSData *jsonData = [jsonStr dataUsingEncoding:NSUTF8StringEncoding];
NSError *errorJson;
id noSummary = [NSJSONSerialization JSONObjectWithData:jsonData options:NSJSONReadingMutableLeaves error:&errorJson];
二 object类转为jsonstr
NSData * jsonData = [NSJSONSerialization dataWithJSONObject:@“object 类” options:0 error:nil];
NSString *jsonString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
