网络请求获取数据 拿到data 转json字符串

NSString *jsonString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];

json字符串转字典

- (NSDictionary *)dictionaryWithJsonString:(NSString *)jsonString {
    if (jsonString == nil) {
        return nil;
    }
    
    NSData *jsonData = [jsonString dataUsingEncoding:NSUTF8StringEncoding];
    NSError *err;
    NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:jsonData options:NSJSONReadingMutableContainers error:&err];
    if(err) {
        NSLog(@"json解析失败：%@",err);
        return nil;
    }
    return dic;
    
}